Mailing List Archive: MythTV: Users

Cutting commercials without expensive transcoding

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lreed at linuxcare

Mar 11, 2004, 9:22 PM

Post #1 of 26 (2994 views)
Permalink

Cutting commercials without expensive transcoding

Hi,

I'm no video expert, so maybe I misunderstand the problem. Or maybe I'm
missing a simple answer that's already there.

I have a PVR250, so my .nuv files are mpeg2 with video and audio
multiplexed in them. After I've marked the commercials (i.e., started
with myth's guesses and tweaked them using the built-in cut editor), I'd
like to do two things:

1. Remove the dreaded commercials in order to shrink the file.

and optionally

2. convert to a plain mpeg2 for use in burning a DVD. (The issue here
may be my poor DVD authoring s/w. mplayer plays the unmolested .nuv
files. OTOH, mplayer will play almost anything.)

I've tried using various methods to accomplish #1: the built-in
transcoding (press 'x'), nuvexport, etc. The problem with all of them
is that they do time-consuming transcoding.

I don't want to change the bit rate or the format, I just want to lift
the parts that have the actual program, leaving behind the ads. It
seems that that should take, in theory, about as much time as it takes
to read the parts of the original file that I care about and write them
out. No serious computation, though maybe a bit of knitting around the
edges.

So,

a. Am I missing something that this makes this far more computationally
intensive than I think?

b. Am I missing an existing tool that does what I want?

Thanks,
Len

mythtv at scottnic

Mar 11, 2004, 10:58 PM

Post #2 of 26 (2975 views)
Permalink

RE: Cutting commercials without expensive transcoding [In reply to]

> I don't want to change the bit rate or the format, I just want to lift
> the parts that have the actual program, leaving behind the ads. It
> seems that that should take, in theory, about as much time as it takes
> to read the parts of the original file that I care about and write them
> out. No serious computation, though maybe a bit of knitting around the
> edges.

I'm not a video expert by any means, but I'm pretty sure that this doesn't
work due to the nature of MPEG video. MPEG isn't encoded as a bunch of
single frames, but rather as "groups of pictures" (GOP), and if you try to
cut a video file in the middle of a GOP you'll most likely lose sync with
the audio.

If you only cut between GOPs the audio will sync better but you don't get
frame-accurate cuts (i.e. the last 1/2 second of a commercial would still be
there).

Now the video experts can jump in and correct me.

Scott

---
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papenfuss at juneau

Mar 12, 2004, 6:14 AM

Post #3 of 26 (2972 views)
Permalink

Re: Cutting commercials without expensive transcoding [In reply to]

I believe this is referred to in mythtv-land as direct mpeg stream
chopping. I think it's a work in progress, as I'm kinda waiting for the same
thing. In the meantime, I've played with 'GOPChop' to do the cutting. It more
or less works, but it produces some artifacts around the cutpoints, and
mutilates the audio stream. MPlayer will still play it properly, but when
stripped, the audio type isn't recognized:

mpeg2desc -a0 < uncutfile.mpg > deleteme2.aud
file deleteme2.aud -> deleteme2.aud: MP2, 192 kBits, 48 kHz, Stereo

mpeg2desc -a0 < cutfile.mpg > deleteme2.aud
file deleteme.aud -> deleteme.aud: data

Along the same lines as the direct mpeg chopping, has anyone thought
about trying to incorporate the compression-domain transcoding for mpeg2 for a
"lightweight" transcoder? Something like the relatively new 'tcrequant'
component of the transcode package? Maybe as part of an "archive to disk"
module for quick quality reduction to fit a high-quality recording onto a disk
(SVCD, mini-DVD, or DVD)? Just a thought.

-Cory

On Thu, 11 Mar 2004, Len Reed wrote:

> Hi,
>
> I'm no video expert, so maybe I misunderstand the problem. Or maybe I'm
> missing a simple answer that's already there.
>
> I have a PVR250, so my .nuv files are mpeg2 with video and audio
> multiplexed in them. After I've marked the commercials (i.e., started
> with myth's guesses and tweaked them using the built-in cut editor), I'd
> like to do two things:
>
> 1. Remove the dreaded commercials in order to shrink the file.
>
> and optionally
>
> 2. convert to a plain mpeg2 for use in burning a DVD. (The issue here
> may be my poor DVD authoring s/w. mplayer plays the unmolested .nuv
> files. OTOH, mplayer will play almost anything.)
>
>
> I've tried using various methods to accomplish #1: the built-in
> transcoding (press 'x'), nuvexport, etc. The problem with all of them
> is that they do time-consuming transcoding.
>
> I don't want to change the bit rate or the format, I just want to lift
> the parts that have the actual program, leaving behind the ads. It
> seems that that should take, in theory, about as much time as it takes
> to read the parts of the original file that I care about and write them
> out. No serious computation, though maybe a bit of knitting around the
> edges.
>
> So,
>
> a. Am I missing something that this makes this far more computationally
> intensive than I think?
>
> b. Am I missing an existing tool that does what I want?
>
> Thanks,
> Len
>
>

--
*************************************************************************
* The prime directive of Linux: *
* - learn what you don't know, *
* - teach what you do. *
* (Just my 20 USm$) *
*************************************************************************

tony at maro

Mar 12, 2004, 8:07 AM

Post #4 of 26 (2933 views)
Permalink

Re: Cutting commercials without expensive transcoding [In reply to]

> I would love to be able to clip a two-minute section of some show and
> email it to a friend.

Actually, you could easily do this. Just set a commercial cutlist to
cut everything EXCEPT the 2 min section, then use nuvexport to dump to a
separate DIVX or whatever, incorporating the cutlist information.

Sure, nuvexport is console-based, but it still works!

-Tony

pc-mythtv04 at crowcastle

Mar 12, 2004, 8:07 AM

Post #5 of 26 (2972 views)
Permalink

RE: Cutting commercials without expensive transcoding [In reply to]

On Fri, 2004-03-12 at 00:58, Scott Nicholson wrote:
> I'm not a video expert by any means, but I'm pretty sure that this doesn't
> work due to the nature of MPEG video. MPEG isn't encoded as a bunch of
> single frames, but rather as "groups of pictures" (GOP), and if you try to
> cut a video file in the middle of a GOP you'll most likely lose sync with
> the audio.
>
> If you only cut between GOPs the audio will sync better but you don't get
> frame-accurate cuts (i.e. the last 1/2 second of a commercial would still be
> there).
>
> Now the video experts can jump in and correct me.

Yeah, you have to recompress a tiny fraction of your video, at least in
theory. In practice, you have a scene change at the points where you
want to cut, so you should be able to get a perfect cut almost every
time.

As to Myth, I expect we all have a picture in our heads of a neat user
interface where we can define and adjust cut points (with the aid of
multiple commercial-detection algorithms), and then use those cut points
to watch the show, shrink the file, transcode if desired, and export the
file.

I would love to be able to clip a two-minute section of some show and
email it to a friend.

--PC

ho_9 at hotmail

Mar 12, 2004, 8:52 AM

Post #6 of 26 (2973 views)
Permalink

RE: Cutting commercials without expensive transcoding [In reply to]

>From: Len Reed <lreed [at] linuxcare>
>Reply-To: Discussion about mythtv <mythtv-users [at] mythtv>
>To: mythtv-users [at] mythtv
>Subject: [mythtv-users] Cutting commercials without expensive transcoding
>Date: Thu, 11 Mar 2004 23:22:05 -0500
>
>Hi,
>
>I'm no video expert, so maybe I misunderstand the problem. Or maybe I'm
>missing a simple answer that's already there.
>
>I have a PVR250, so my .nuv files are mpeg2 with video and audio
>multiplexed in them. After I've marked the commercials (i.e., started with
>myth's guesses and tweaked them using the built-in cut editor), I'd like to
>do two things:
>
>1. Remove the dreaded commercials in order to shrink the file.
>
>and optionally
>
>2. convert to a plain mpeg2 for use in burning a DVD. (The issue here may
>be my poor DVD authoring s/w. mplayer plays the unmolested .nuv files.
>OTOH, mplayer will play almost anything.)
>
>
>I've tried using various methods to accomplish #1: the built-in transcoding
>(press 'x'), nuvexport, etc. The problem with all of them is that they do
>time-consuming transcoding.
>
>I don't want to change the bit rate or the format, I just want to lift the
>parts that have the actual program, leaving behind the ads. It seems that
>that should take, in theory, about as much time as it takes to read the
>parts of the original file that I care about and write them out. No
>serious computation, though maybe a bit of knitting around the edges.
>
>So,
>
>a. Am I missing something that this makes this far more computationally
>intensive than I think?
>
>b. Am I missing an existing tool that does what I want?
>
>Thanks,
>Len
>
>_______________________________________________
>mythtv-users mailing list
>mythtv-users [at] mythtv
>http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users

This may not be a correct answer to your question because
I edit/trancode for SVCD and not DVD, but this is what I do:

I use avidemux2. I allows me to cut commercials and
transcode from 3500/4400 vbr to 2200 for SVCD and it
only takes approx. 48 minutes for a 1/2 hour show (I think
that's around 22 minutes with commercials removed). I do
have to multiplex the video/audio after transcoding since
avidemux2 splits it when saving after transcoding, so the
total time for a 1/2 hour show including editing, transcoding
and remuxing is about 55 minutes.

I would think that if you record in a proper bitrate for DVD
and using a DVD format (I forget the option for the ivtv
driver but the value is 14 [DVD Special in Myth?]) and cut
commercials to a key frame (not hard to do since
commercial breaks are usually surrounded by some black
frames) you should be able to do what you want with
avidemux2. Since you would not be transcoding at all it
should even be faster than it takes me (though I haven't
tried saving edited mpegs without transcoding).

The caveats are: make sure you start with DVD acceptible
data if you don't want to transcode, you have to manually
edit the mpegs (avidemux2 cannot use the cutlist) and,
most importantly, I haven't tried exactly what you are
attempting, so it may not really work.

All that being said, I believe other people are using
avidemux2 to do what you want and are having some
success. You could check the forums at the avidemux2
site for more info.

HTH!

-- Harry O.

P. S. Just reread your post more carefully. Cut the
program and leave the commercials? Who are you,
Bob Sagat (or maybe A.C. Nielsen)? Above still
applies, just changes what you cut and what you keep.

_________________________________________________________________
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lists at forevermore

Mar 12, 2004, 10:31 AM

Post #7 of 26 (2973 views)
Permalink

RE: Cutting commercials without expensive transcoding [In reply to]

> I use avidemux2. I allows me to cut commercials and
> transcode from 3500/4400 vbr to 2200 for SVCD and it
> only takes approx. 48 minutes for a 1/2 hour show

If anyone is interested, I'd be more than happy to add a module like
this to nuvexport... It sounds like a relatively easy script.

--
Chris Petersen
Programmer / Web Designer
Silicon Mechanics: http://www.siliconmechanics.com/
Blade Servers: http://www.siliconmechanics.com/c292/blade-server.php
1U Servers: http://www.siliconmechanics.com/c272/1u-server.php

_______________________________________________
mythtv-users mailing list
mythtv-users [at] mythtv
http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users

jcollins at asgardsrealm

Mar 12, 2004, 11:13 AM

Post #8 of 26 (2944 views)
Permalink

Re: Cutting commercials without expensive transcoding [In reply to]

On Fri, Mar 12, 2004 at 09:31:31AM -0800, Chris Petersen wrote:
> > I use avidemux2. I allows me to cut commercials and
> > transcode from 3500/4400 vbr to 2200 for SVCD and it
> > only takes approx. 48 minutes for a 1/2 hour show
>
> If anyone is interested, I'd be more than happy to add a module like
> this to nuvexport... It sounds like a relatively easy script.

Sounds like a useful addition.

--
Jamin W. Collins

Remember, root always has a loaded gun. Don't run around with it unless
you absolutely need it. -- Vineet Kumar

ray at comarre

Mar 12, 2004, 11:26 AM

Post #9 of 26 (2972 views)
Permalink

RE: Cutting commercials without expensive transcoding [In reply to]

At 09:31 AM 3/12/2004 -0800, Chris Petersen wrote:
> > I use avidemux2. I allows me to cut commercials and
> > transcode from 3500/4400 vbr to 2200 for SVCD and it
> > only takes approx. 48 minutes for a 1/2 hour show

I've only skimmed this thread, but I think some responses in it are missing
the point of the original question. Let me use a separate example to try to
illustrate.

If I capture video directly as DivX (using vcr/avifile, or mplayer, or
whatever), I can use VirtualDub to edit out commercials. If I am willing to
accept the small imperfections that go with "keyframe editing", I can run
VirtualDub in "Direct Stream Copy" mode. So I can delete commercials by
hand, then process a file, all VERY quickly. Processing a 2-hour source
file takes me about 5 minutes (plus the editing time, which varies a lot
depending on how many commercial breaks are present, but is generally in
the 2-10 minute range).

Compared to this speed, "approx. 48 minutes for a 1/2 hour show" is a long
time, not an "only". That sort of time is, I'm sure, what the original
poster meant by "expensive". The speed advantage I get occurs because the
only processing needed is to keep the audio and video in sync (that is, get
things right at the container level), not to recode either the audio or the
video itself.

Keyframe editing is not perfect ... small snippets of commercials remain
after editing ... but I find it "good enough", given the speed benefit it
offers. I think the original poster is looking for some similar capability
in Myth ... the ability to clip out short bits ... most of the commercials,
for example ... without having to recode what remains.

The problem with providing this sort of quick-edit capability for Myth is
codecs. The internal encoding format used by Myth is non-standard, so an
outside application like VD can't handle it. The original poster has a
PVR250 and wanted to treat MPEG2 this way ... this should be doable in
principle, but in fact I don't know of any actual software (I've only
looked for Open Source/free software) that will do it ... I'm guessing due
to patent issues, but I really do not know why no one offers the ability to
keyframe edit MPEG2.

I did find a reference to a shareware (Windows) product called MPEG2VCR.
Its description say the following:

"No re-encoding when editing DVD-compliant MPEG2 captures from the latest
USB/DVD capture boxes. When using these sources to create a movie for DVD
burning, you will not have to wait for many hours while your movie is
re-encoded. Instead, your edited video will be written back to disk as fast
as any disk-to-disk copy operation."

See http://www.womble.com/products.htm for more details. But a $US 70, it
is not a cheap solution.

lists at forevermore

Mar 12, 2004, 11:48 AM

Post #10 of 26 (2960 views)
Permalink

Re: Cutting commercials without expensive transcoding [In reply to]

> > If anyone is interested, I'd be more than happy to add a module like
> > this to nuvexport... It sounds like a relatively easy script.
> Sounds like a useful addition.

Now that I read this, I feel I should qualify the statement.. I'd be
happy to add one if someone wrote one and sent it to me. I don't have
any way to write/test said module myself.

--
Chris Petersen
Programmer / Web Designer
Silicon Mechanics: http://www.siliconmechanics.com/
Blade Servers: http://www.siliconmechanics.com/c292/blade-server.php
1U Servers: http://www.siliconmechanics.com/c272/1u-server.php

_______________________________________________
mythtv-users mailing list
mythtv-users [at] mythtv
http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users

lists at forevermore

Mar 12, 2004, 11:52 AM

Post #11 of 26 (2970 views)
Permalink

RE: Cutting commercials without expensive transcoding [In reply to]

> If I capture video directly as DivX (using vcr/avifile, or mplayer, or
> whatever)

And if you do that in mythtv to mpeg4 or rtjpeg, transcoding works just
fine and takes about 3 minutes per half-hour show on my box to cut out
the commercials, since it only needs to reencode a few frames around the
cut-out GOP to keep things in sync.

And yes, you are correct that this thread went a bit off course from the
original poster's question. As to that question, search the dev list
archives. There is an active attempt to add this "quick" cutting of
mpeg2 files to mythtranscode, but there are some codec/sync issues that
are currently blocking its imminent completion.

--
Chris Petersen
Programmer / Web Designer
Silicon Mechanics: http://www.siliconmechanics.com/
Blade Servers: http://www.siliconmechanics.com/c292/blade-server.php
1U Servers: http://www.siliconmechanics.com/c272/1u-server.php

_______________________________________________
mythtv-users mailing list
mythtv-users [at] mythtv
http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users

thomas at boerkel

Mar 12, 2004, 12:12 PM

Post #12 of 26 (2972 views)
Permalink

Re: Cutting commercials without expensive transcoding [In reply to]

HI!

Ray Olszewski wrote:
>> > I use avidemux2. I allows me to cut commercials and
>> > transcode from 3500/4400 vbr to 2200 for SVCD and it
>> > only takes approx. 48 minutes for a 1/2 hour show
>

> a PVR250 and wanted to treat MPEG2 this way ... this should be doable in
> principle, but in fact I don't know of any actual software (I've only
> looked for Open Source/free software) that will do it ... I'm guessing
> due to patent issues, but I really do not know why no one offers the
> ability to keyframe edit MPEG2.
>
> I did find a reference to a shareware (Windows) product called MPEG2VCR.
> Its description say the following:
>
> "No re-encoding when editing DVD-compliant MPEG2 captures from the
> latest USB/DVD capture boxes. When using these sources to create a movie
> for DVD burning, you will not have to wait for many hours while your
> movie is re-encoded. Instead, your edited video will be written back to
> disk as fast as any disk-to-disk copy operation."
>
> See http://www.womble.com/products.htm for more details. But a $US 70,
> it is not a cheap solution.

Actually, avidemux2 can edit the PVR's MPEG2 files quickly, without
reencoding.

But a commandline tool, that processes the cutlist and is being called
by Myth, would be much better. Just as you can do it within Myth with
MPEG4 recordings AFAIK. I thought this is also possible with MPEG2, but
somehow broken in 0.14.

Thomas

stanb at panix

Mar 12, 2004, 5:13 PM

Post #13 of 26 (2962 views)
Permalink

Re: Cutting commercials without expensive transcoding [In reply to]

On Fri, Mar 12, 2004 at 09:31:31AM -0800, Chris Petersen wrote:
> > I use avidemux2. I allows me to cut commercials and
> > transcode from 3500/4400 vbr to 2200 for SVCD and it
> > only takes approx. 48 minutes for a 1/2 hour show
>
> If anyone is interested, I'd be more than happy to add a module like
> this to nuvexport... It sounds like a relatively easy script.

Wow! Count me in!

--
"They that would give up essential liberty for temporary safety deserve
neither liberty nor safety."
-- Benjamin Franklin

tommy at home

Mar 13, 2004, 9:38 AM

Post #14 of 26 (2976 views)
Permalink

Re: Cutting commercials without expensive transcoding [In reply to]

> Actually, avidemux2 can edit the PVR's MPEG2 files quickly, without
> reencoding.
>
> But a commandline tool, that processes the cutlist and is being called
> by Myth, would be much better. Just as you can do it within Myth with
> MPEG4 recordings AFAIK. I thought this is also possible with MPEG2, but
> somehow broken in 0.14.

Would mpgtx (http://mpgtx.sourceforge.net/) fit this description?

--
"I went to the museum where they had all the heads and arms from the
statues that are in all the other museums."
-- Steven Wright

james at mauibay

Mar 13, 2004, 12:11 PM

Post #15 of 26 (2957 views)
Permalink

Re: Cutting commercials without expensive transcoding [In reply to]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

On Thursday 11 March 2004 6:22 pm, Len Reed wrote:
> Hi,
>
> I'm no video expert, so maybe I misunderstand the problem. Or maybe I'm
> missing a simple answer that's already there.
>
> I have a PVR250, so my .nuv files are mpeg2 with video and audio
> multiplexed in them. After I've marked the commercials (i.e., started
> with myth's guesses and tweaked them using the built-in cut editor), I'd
> like to do two things:
>
> 1. Remove the dreaded commercials in order to shrink the file.

I also use PVR250 output. I still remove commecials manually with avidemux2
when I want to archive to CVD or DVD. I only cut on keyframe boundaries.

> and optionally
>
> 2. convert to a plain mpeg2 for use in burning a DVD. (The issue here
> may be my poor DVD authoring s/w. mplayer plays the unmolested .nuv
> files. OTOH, mplayer will play almost anything.)

This has been discussed on this list, with specific steps. It's very easy. The
output of the PVR250 will work fine on a DVD with no transcoding. I just cut
out the commercials with avidemux2, remultiplex with DVD nav headers and pass
it to dvdauthor. I have burned many DVDs and CVDs from non-transcoded PVR250
output captured from my MythTV box. The video format is fine, the audio
format seems to work on most DVD players also. (Technically, I think standard
players aren't required to play MPEG audio is AC3 audio isn't present, but I
haven't heard of a case yet where it doesn't work anyway.)

>
> I've tried using various methods to accomplish #1: the built-in
> transcoding (press 'x'), nuvexport, etc. The problem with all of them
> is that they do time-consuming transcoding.

I'm not aware that anybody has a fully automated process for this from within
myth. There are people working on it though.

> I don't want to change the bit rate or the format, I just want to lift
> the parts that have the actual program, leaving behind the ads. It
> seems that that should take, in theory, about as much time as it takes
> to read the parts of the original file that I care about and write them
> out. No serious computation, though maybe a bit of knitting around the
> edges.

The basic key to this is to capture in a DVD-compliant stream format in the
first place. You should only need to transcode if your captured stream is the
wrong resolution or bitrate.

> So,
>
> a. Am I missing something that this makes this far more computationally
> intensive than I think?

Nope. It's more a matter of automation. We need a tool that can accurately do
keyframe edits based on the cutlist, remultiplex the results for dvdauthor,
then create and burn a DVD image.

> b. Am I missing an existing tool that does what I want?

We all are. ;) As is common for open source tools, the building blocks all
exist. We simply need to build something polished with them. MythTV is a
shining example of this process, and it's still relatively young yet.

> Thanks,
> Len
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_______________________________________________
mythtv-users mailing list
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http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users

papenfuss at juneau

Mar 13, 2004, 1:59 PM

Post #16 of 26 (2976 views)
Permalink

Re: Cutting commercials without expensive transcoding [In reply to]

OK... aside from the apparent problem I have with finding the right
tool for the job, I believe that avidemux2 is the closest so far... found only
recently by following this thread, I may add. I've got a test capture from my
PVR-250 that I'm playing with mastering both DVDs and SVCDs. Here are a few
random issues that I would like to both share with everyone, and perhaps the
ramifications of them:

- The hardware encoders don't have the benefit of a 2-pass encoding scheme
(being a causal device and all... :) or high-quality denoising, so they don't
necessarily make the right choices on I/P/B frames all the time. It makes
sense to me that I frames should be used on large scene changes... but that's
not necessarily done with the raw captured streams and causes wasted bandwidth.
For the best quality/bitrate ratio, post-processing (i.e. *re-encoding*) will
be necessary.

- The avidemux program still has some issues with processing streams. Using
the DVD-PS output file type produces DVD-compatible streams that are much
larger than ones manually mux'd with tcmplex. Unfortunately, extracting (or
processing) video and audio streams separately generally tends to cause sync
problems. Also, is a DVD-PS (with NAV packets) acceptable as an SVCD stream?

There are a few different fundamental goals I can see would be useful for
arching mythtv folks:

1. Simple, fast "VCR" functionality... quick and simple recording onto DVD from
a PVR-[23]50 set to record in a DVD compatible format. This would preferrably
have commercial-cutting ability, but that's all.
Advantages: Quick, easy (especially if no commerical cutting), CPU-efficient.
Disadvantages: Not the most efficient use of space, can't specify
"master-quality" recordings and then "archival-quality" DVD or SVCD since it's
recorded/encoded in the final format.

2. Efficient/convenient, "Archive" functionality... Recording at high-quality
("Master copy"). Commercial cutting and transcoding in post-processing. This
allows for the best quality/bitrate ratio and makes archiving to less expensive
media (e.g. SVCD) or more pack more episodes onto DVD's. Especially important
for the SVCD/DVD decision, as the resolutions aren't compatible (480x480 for
SVCD, 352x480 for DVD, and 704x480 which is gross overkill for cable-quality
captures).

3. Space efficient, "Computer archive" functionality. Similar to #2, but with
the ultimate goal of MPEG4 archiving on computer media. Once the requirement
of set-top box compatibility is removed, anything mplayer can play is valid.

Did I miss anything? :)

-Cory

On Sat, 13 Mar 2004, James L. Paul wrote:

> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> On Thursday 11 March 2004 6:22 pm, Len Reed wrote:
> > Hi,
> >
> > I'm no video expert, so maybe I misunderstand the problem. Or maybe I'm
> > missing a simple answer that's already there.
> >
> > I have a PVR250, so my .nuv files are mpeg2 with video and audio
> > multiplexed in them. After I've marked the commercials (i.e., started
> > with myth's guesses and tweaked them using the built-in cut editor), I'd
> > like to do two things:
> >
> > 1. Remove the dreaded commercials in order to shrink the file.
>
> I also use PVR250 output. I still remove commecials manually with avidemux2
> when I want to archive to CVD or DVD. I only cut on keyframe boundaries.
>
> > and optionally
> >
> > 2. convert to a plain mpeg2 for use in burning a DVD. (The issue here
> > may be my poor DVD authoring s/w. mplayer plays the unmolested .nuv
> > files. OTOH, mplayer will play almost anything.)
>
> This has been discussed on this list, with specific steps. It's very easy. The
> output of the PVR250 will work fine on a DVD with no transcoding. I just cut
> out the commercials with avidemux2, remultiplex with DVD nav headers and pass
> it to dvdauthor. I have burned many DVDs and CVDs from non-transcoded PVR250
> output captured from my MythTV box. The video format is fine, the audio
> format seems to work on most DVD players also. (Technically, I think standard
> players aren't required to play MPEG audio is AC3 audio isn't present, but I
> haven't heard of a case yet where it doesn't work anyway.)
>
> >
> > I've tried using various methods to accomplish #1: the built-in
> > transcoding (press 'x'), nuvexport, etc. The problem with all of them
> > is that they do time-consuming transcoding.
>
> I'm not aware that anybody has a fully automated process for this from within
> myth. There are people working on it though.
>
> > I don't want to change the bit rate or the format, I just want to lift
> > the parts that have the actual program, leaving behind the ads. It
> > seems that that should take, in theory, about as much time as it takes
> > to read the parts of the original file that I care about and write them
> > out. No serious computation, though maybe a bit of knitting around the
> > edges.
>
> The basic key to this is to capture in a DVD-compliant stream format in the
> first place. You should only need to transcode if your captured stream is the
> wrong resolution or bitrate.
>
> > So,
> >
> > a. Am I missing something that this makes this far more computationally
> > intensive than I think?
>
> Nope. It's more a matter of automation. We need a tool that can accurately do
> keyframe edits based on the cutlist, remultiplex the results for dvdauthor,
> then create and burn a DVD image.
>
> > b. Am I missing an existing tool that does what I want?
>
> We all are. ;) As is common for open source tools, the building blocks all
> exist. We simply need to build something polished with them. MythTV is a
> shining example of this process, and it's still relatively young yet.
>
> > Thanks,
> > Len
> -----BEGIN PGP SIGNATURE-----
> Version: GnuPG v1.2.2 (GNU/Linux)
>
> iD8DBQFAU1zwT8BYaKRUpkQRAhMkAKCY3Cnu4QblwIXNuE1gkn896w15YQCgkzDR
> jMksFwmCoK+zFIydGN2Eu+I=
> =79wi
> -----END PGP SIGNATURE-----
> _______________________________________________
> mythtv-users mailing list
> mythtv-users [at] mythtv
> http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users
>

--
*************************************************************************
* The prime directive of Linux: *
* - learn what you don't know, *
* - teach what you do. *
* (Just my 20 USm$) *
*************************************************************************

james at mauibay

Mar 13, 2004, 4:23 PM

Post #17 of 26 (2962 views)
Permalink

Re: Cutting commercials without expensive transcoding [In reply to]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

On Saturday 13 March 2004 10:59 am, papenfuss [at] juneau wrote:
> OK... aside from the apparent problem I have with finding the right
> tool for the job, I believe that avidemux2 is the closest so far... found
> only recently by following this thread, I may add. I've got a test capture
> from my PVR-250 that I'm playing with mastering both DVDs and SVCDs. Here
> are a few random issues that I would like to both share with everyone, and
> perhaps the ramifications of them:
>
> - The hardware encoders don't have the benefit of a 2-pass encoding scheme
> (being a causal device and all... :) or high-quality denoising, so they
> don't necessarily make the right choices on I/P/B frames all the time. It
> makes sense to me that I frames should be used on large scene changes...
> but that's not necessarily done with the raw captured streams and causes
> wasted bandwidth. For the best quality/bitrate ratio, post-processing (i.e.
> *re-encoding*) will be necessary.

Re-encoding isn't going to restore quality that isn't there. Also, considering
that the quality of the cable TV signal feeding the PVRx50 card is much lower
than DVD quality to begin with, we're not talking about creating high-quality
DVDs, I thought we were talking only about burning some commercial-cut TV
shows to a standard format on plastic. ;)

> - The avidemux program still has some issues with processing streams.
> Using the DVD-PS output file type produces DVD-compatible streams that are
> much larger than ones manually mux'd with tcmplex. Unfortunately,
> extracting (or processing) video and audio streams separately generally
> tends to cause sync problems. Also, is a DVD-PS (with NAV packets)
> acceptable as an SVCD stream?

I don't understand. Manually muxing has nothing to do with file sizes. I've
had audio sync issues when capturing to elemental (non-PS) separate streams,
but never a problem with the PS streams output by my PVR250's. Demuxing and
remuxing my PVR250 streams has never produced any audio sync issues for me at
all.

I assume that any DVD-PS stream is an incorrect format for SVCD, since the
SVCD stream specs are not DVD-compliant. So this answer would be no. I don't
see how it's relevant though, since the PVR250 doesn't output PS streams with
DVD NAV packets if I understand correctly. I believe it's necessary to remux
the PS stream to insert the NAV placeholders. And again, no, this should not
create any audio sync issues.

> There are a few different fundamental goals I can see would be useful for
> arching mythtv folks:
>
> 1. Simple, fast "VCR" functionality... quick and simple recording onto DVD
> from a PVR-[23]50 set to record in a DVD compatible format. This would
> preferrably have commercial-cutting ability, but that's all.
> Advantages: Quick, easy (especially if no commerical cutting),
> CPU-efficient. Disadvantages: Not the most efficient use of space, can't
> specify
> "master-quality" recordings and then "archival-quality" DVD or SVCD since
> it's recorded/encoded in the final format.

This is basically my own goal. I do it manually now. I don't feel the
disadvantage as strongly as you imply it to be, since if I really want to
shrink the size requirements I simply requantize the video instead of
re-encoding.

> 2. Efficient/convenient, "Archive" functionality... Recording at
> high-quality ("Master copy"). Commercial cutting and transcoding in
> post-processing. This allows for the best quality/bitrate ratio and makes
> archiving to less expensive media (e.g. SVCD) or more pack more episodes
> onto DVD's. Especially important for the SVCD/DVD decision, as the
> resolutions aren't compatible (480x480 for SVCD, 352x480 for DVD, and
> 704x480 which is gross overkill for cable-quality captures).

Again, I've had good results with tcrequant instead of transcoding or
re-encoding the whole stream. Some of the archive DVDs I've done of animated
cartoons (think "Family Guy") requant very well and I've been able to fit 6
hours or so on a single DVD with good quality.

> 3. Space efficient, "Computer archive" functionality. Similar to #2, but
> with the ultimate goal of MPEG4 archiving on computer media. Once the
> requirement of set-top box compatibility is removed, anything mplayer can
> play is valid.

Agreed. Many issues drop away if you aren't targetting playability in common
set-top DVD players. :)

>
> Did I miss anything? :)

Only things that come to mind right now are:

4. Instead of burning 1 show per disk, an interface for collecting media-ready
titles that can be accumulated and selected for burning multiple captures to
a single disk.

5. The obvious menu-generation features that would be welcomed by users of the
preceeding #4. ;)

> -Cory
>
> On Sat, 13 Mar 2004, James L. Paul wrote:
> > -----BEGIN PGP SIGNED MESSAGE-----
> > Hash: SHA1
> >
> > On Thursday 11 March 2004 6:22 pm, Len Reed wrote:
> > > Hi,
> > >
> > > I'm no video expert, so maybe I misunderstand the problem. Or maybe
> > > I'm missing a simple answer that's already there.
> > >
> > > I have a PVR250, so my .nuv files are mpeg2 with video and audio
> > > multiplexed in them. After I've marked the commercials (i.e., started
> > > with myth's guesses and tweaked them using the built-in cut editor),
> > > I'd like to do two things:
> > >
> > > 1. Remove the dreaded commercials in order to shrink the file.
> >
> > I also use PVR250 output. I still remove commecials manually with
> > avidemux2 when I want to archive to CVD or DVD. I only cut on keyframe
> > boundaries.
> >
> > > and optionally
> > >
> > > 2. convert to a plain mpeg2 for use in burning a DVD. (The issue here
> > > may be my poor DVD authoring s/w. mplayer plays the unmolested .nuv
> > > files. OTOH, mplayer will play almost anything.)
> >
> > This has been discussed on this list, with specific steps. It's very
> > easy. The output of the PVR250 will work fine on a DVD with no
> > transcoding. I just cut out the commercials with avidemux2, remultiplex
> > with DVD nav headers and pass it to dvdauthor. I have burned many DVDs
> > and CVDs from non-transcoded PVR250 output captured from my MythTV box.
> > The video format is fine, the audio format seems to work on most DVD
> > players also. (Technically, I think standard players aren't required to
> > play MPEG audio is AC3 audio isn't present, but I haven't heard of a case
> > yet where it doesn't work anyway.)
> >
> > > I've tried using various methods to accomplish #1: the built-in
> > > transcoding (press 'x'), nuvexport, etc. The problem with all of them
> > > is that they do time-consuming transcoding.
> >
> > I'm not aware that anybody has a fully automated process for this from
> > within myth. There are people working on it though.
> >
> > > I don't want to change the bit rate or the format, I just want to lift
> > > the parts that have the actual program, leaving behind the ads. It
> > > seems that that should take, in theory, about as much time as it takes
> > > to read the parts of the original file that I care about and write them
> > > out. No serious computation, though maybe a bit of knitting around the
> > > edges.
> >
> > The basic key to this is to capture in a DVD-compliant stream format in
> > the first place. You should only need to transcode if your captured
> > stream is the wrong resolution or bitrate.
> >
> > > So,
> > >
> > > a. Am I missing something that this makes this far more computationally
> > > intensive than I think?
> >
> > Nope. It's more a matter of automation. We need a tool that can
> > accurately do keyframe edits based on the cutlist, remultiplex the
> > results for dvdauthor, then create and burn a DVD image.
> >
> > > b. Am I missing an existing tool that does what I want?
> >
> > We all are. ;) As is common for open source tools, the building blocks
> > all exist. We simply need to build something polished with them. MythTV
> > is a shining example of this process, and it's still relatively young
> > yet.
> >
> > > Thanks,
> > > Len
> >
> > -----BEGIN PGP SIGNATURE-----
> > Version: GnuPG v1.2.2 (GNU/Linux)
> >
> > iD8DBQFAU1zwT8BYaKRUpkQRAhMkAKCY3Cnu4QblwIXNuE1gkn896w15YQCgkzDR
> > jMksFwmCoK+zFIydGN2Eu+I=
> > =79wi
> > -----END PGP SIGNATURE-----
> > _______________________________________________
> > mythtv-users mailing list
> > mythtv-users [at] mythtv
> > http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users
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_______________________________________________
mythtv-users mailing list
mythtv-users [at] mythtv
http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users

david.blevins at visi

Mar 13, 2004, 5:55 PM

Post #18 of 26 (2967 views)
Permalink

Re: Cutting commercials without expensive transcoding [In reply to]

On Sat, Mar 13, 2004 at 01:23:26PM -1000, James L. Paul wrote:
>
> Again, I've had good results with tcrequant instead of transcoding or
> re-encoding the whole stream. Some of the archive DVDs I've done of animated
> cartoons (think "Family Guy") requant very well and I've been able to fit 6
> hours or so on a single DVD with good quality.

Wow, about 90% of what I capture is cartoons, this would be great for
me. Can you post some notes on your process?

-David

anthony_myth at hotmail

Mar 13, 2004, 9:23 PM

Post #19 of 26 (2969 views)
Permalink

RE: Cutting commercials without expensive transcoding [In reply to]

Is there anyway to pass a cutlist to avidemux2? I have looked at the
commandline parameters in the docs but it doesn't appear that there is a
way?

--Anthony

> -----Original Message-----
> From: mythtv-users-bounces [at] mythtv [mailto:mythtv-users-
> bounces [at] mythtv] On Behalf Of James L. Paul
> Sent: Saturday, March 13, 2004 1:12 PM
> To: Discussion about mythtv
> Subject: Re: [mythtv-users] Cutting commercials without expensive
> transcoding
>
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> On Thursday 11 March 2004 6:22 pm, Len Reed wrote:
> > Hi,
> >
> > I'm no video expert, so maybe I misunderstand the problem. Or maybe I'm
> > missing a simple answer that's already there.
> >
> > I have a PVR250, so my .nuv files are mpeg2 with video and audio
> > multiplexed in them. After I've marked the commercials (i.e., started
> > with myth's guesses and tweaked them using the built-in cut editor), I'd
> > like to do two things:
> >
> > 1. Remove the dreaded commercials in order to shrink the file.
>
> I also use PVR250 output. I still remove commecials manually with
> avidemux2
> when I want to archive to CVD or DVD. I only cut on keyframe boundaries.
>
> > and optionally
> >
> > 2. convert to a plain mpeg2 for use in burning a DVD. (The issue here
> > may be my poor DVD authoring s/w. mplayer plays the unmolested .nuv
> > files. OTOH, mplayer will play almost anything.)
>
> This has been discussed on this list, with specific steps. It's very easy.
> The
> output of the PVR250 will work fine on a DVD with no transcoding. I just
> cut
> out the commercials with avidemux2, remultiplex with DVD nav headers and
> pass
> it to dvdauthor. I have burned many DVDs and CVDs from non-transcoded
> PVR250
> output captured from my MythTV box. The video format is fine, the audio
> format seems to work on most DVD players also. (Technically, I think
> standard
> players aren't required to play MPEG audio is AC3 audio isn't present, but
> I
> haven't heard of a case yet where it doesn't work anyway.)
>
> >
> > I've tried using various methods to accomplish #1: the built-in
> > transcoding (press 'x'), nuvexport, etc. The problem with all of them
> > is that they do time-consuming transcoding.
>
> I'm not aware that anybody has a fully automated process for this from
> within
> myth. There are people working on it though.
>
> > I don't want to change the bit rate or the format, I just want to lift
> > the parts that have the actual program, leaving behind the ads. It
> > seems that that should take, in theory, about as much time as it takes
> > to read the parts of the original file that I care about and write them
> > out. No serious computation, though maybe a bit of knitting around the
> > edges.
>
> The basic key to this is to capture in a DVD-compliant stream format in
> the
> first place. You should only need to transcode if your captured stream is
> the
> wrong resolution or bitrate.
>
> > So,
> >
> > a. Am I missing something that this makes this far more computationally
> > intensive than I think?
>
> Nope. It's more a matter of automation. We need a tool that can accurately
> do
> keyframe edits based on the cutlist, remultiplex the results for
> dvdauthor,
> then create and burn a DVD image.
>
> > b. Am I missing an existing tool that does what I want?
>
> We all are. ;) As is common for open source tools, the building blocks all
> exist. We simply need to build something polished with them. MythTV is a
> shining example of this process, and it's still relatively young yet.
>
> > Thanks,
> > Len
> -----BEGIN PGP SIGNATURE-----
> Version: GnuPG v1.2.2 (GNU/Linux)
>
> iD8DBQFAU1zwT8BYaKRUpkQRAhMkAKCY3Cnu4QblwIXNuE1gkn896w15YQCgkzDR
> jMksFwmCoK+zFIydGN2Eu+I=
> =79wi
> -----END PGP SIGNATURE-----
> _______________________________________________
> mythtv-users mailing list
> mythtv-users [at] mythtv
> http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users

stanb at panix

Mar 14, 2004, 6:33 AM

Post #20 of 26 (2974 views)
Permalink

Re: Cutting commercials without expensive transcoding [In reply to]

On Sat, Mar 13, 2004 at 01:23:26PM -1000, James L. Paul wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> On Saturday 13 March 2004 10:59 am, papenfuss [at] juneau wrote:
>
> This is basically my own goal. I do it manually now. I don't feel the
> disadvantage as strongly as you imply it to be, since if I really want to
> shrink the size requirements I simply requantize the video instead of
> re-encoding.
>
Mind detailing how you are acomplishing this?

I'm using the following script, but I think it could be improved on,
quite a bit. For example I wish it had a nice selectin interface like
nuvexport.

BTW anyone no why nuvexport doesn't write a good DVD when your captures
are from 350/250 cards?

#!/bin/sh

##################################################################
#
# wrie_dvd
#
# Writes a DVD from a MythTV saved .nuv file (assumeing it was saved
# with a PVR-250 or OVR-350, thus it's already in MPEG2 format)
#
# Argument 1 is the name of the .nuv file
#
################################################################

WORKDIR=work$$

cd /cache/tmp

mkfifo aud0
mkfifo vid0
mkfifo dvdmpg
mpeg2desc -a0 < $1 > aud0 &
mpeg2desc -v0 < $1 > vid0 &
mplex -f 8 -V -o dvdmpg aud0 vid0 &
dvdauthor -o $WORKDIR -f dvdmpg
dvdauthor -o $WORKDIR -T

rm aud0
rm vid0
rm dvdmpg

growisofs -dvd-video -Z /dev/dvd $WORKDIR

rm -r $WORKDIR

--
"They that would give up essential liberty for temporary safety deserve
neither liberty nor safety."
-- Benjamin Franklin

papenfuss at juneau

Mar 14, 2004, 7:56 AM

Post #21 of 26 (2964 views)
Permalink

Re: Cutting commercials without expensive transcoding [In reply to]

> > - The hardware encoders don't have the benefit of a 2-pass encoding scheme
> > (being a causal device and all... :) or high-quality denoising, so they
> > don't necessarily make the right choices on I/P/B frames all the time. It
> > makes sense to me that I frames should be used on large scene changes...
> > but that's not necessarily done with the raw captured streams and causes
> > wasted bandwidth. For the best quality/bitrate ratio, post-processing (i.e.
> > *re-encoding*) will be necessary.
>
> Re-encoding isn't going to restore quality that isn't there. Also, considering
> that the quality of the cable TV signal feeding the PVRx50 card is much lower
> than DVD quality to begin with, we're not talking about creating high-quality
> DVDs, I thought we were talking only about burning some commercial-cut TV
> shows to a standard format on plastic. ;)
>
That's quite true, but I'm talking about the best quality/bitrate
possible. For NTSC captures, anything over 480x480 is wasted resolution. If
you scale that to typical DVD movie MPEG2 bitrate of 3.5 Mbps, the 480x480
shouldn't require more than 2.3 Mbps to obtain the same results. The
PVR-[23]50's tend to look pretty blocky at such low bitrates. If captured at
higher bitrate and then cut back, it can look better than if captured at low
bitrate to start with, since the encoder has the potential advantage of 2-pass
encoding, etc.

> > - The avidemux program still has some issues with processing streams.
> > Using the DVD-PS output file type produces DVD-compatible streams that are
> > much larger than ones manually mux'd with tcmplex. Unfortunately,
> > extracting (or processing) video and audio streams separately generally
> > tends to cause sync problems. Also, is a DVD-PS (with NAV packets)
> > acceptable as an SVCD stream?
>
> I don't understand. Manually muxing has nothing to do with file sizes. I've
> had audio sync issues when capturing to elemental (non-PS) separate streams,
> but never a problem with the PS streams output by my PVR250's. Demuxing and
> remuxing my PVR250 streams has never produced any audio sync issues for me at
> all.

It doesn't seem like it should, but it does. There's much more in a
DVD mpeg stream that audio and video... and lots of choices that can be made.
I did the same thing two different ways... a 1 minute clip muxed with
avidemux's DVD-PS, and the other 'tcmplex -m dvd'. Here are the resulting file
sizes:
21720 test.m2v
1428 test.mp2
23912 test_tcmplexdvdps.mpg
27540 test_avidemuxdvdps.mpg

So, there's 3% overhead for the tcmplex'd one, and 18% overhead for the
avidemux'd one. There's lots of padding inserted from avidemux.

The tcmplex'd version shows this from tcscan and vstrip:
------------- presentation unit [0] ---------------
stream id [0xbb] 121
stream id [0xbe] 123
stream id [0xbf] 242
stream id [0xc0] 722
stream id [0xe0] 11098
12306 packetized elementary stream(s) PES packets found
presentation unit PU [0] contains 121 MPEG video sequence(s)
Average Bitrate is 5000. Min Bitrate is 5000, max is 5000 (CBR)

Summary:
MPEG Packs = 11942
System headers = 121
Padding packets = 123, total bytes = 129436
Private 2 packets = 242, total bytes = 241758
MPEG1 Audio 0 packets = 722, total bytes = 1454500
Video 0 packets = 11098, total bytes = 22202806

and the avidemux'd one shows:
------------- presentation unit [0] ---------------
stream id [0xbb] 61
stream id [0xbe] 3621
stream id [0xbf] 122
stream id [0xc0] 1813
stream id [0xe0] 11879
17496 packetized elementary stream(s) PES packets found
presentation unit PU [0] contains 121 MPEG video sequence(s)
Average Bitrate is 5000. Min Bitrate is 5000, max is 5000 (CBR)

Summary:
MPEG Packs = 13753
System headers = 61
Padding packets = 3621, total bytes = 4031738
Private 2 packets = 122, total bytes = 121878
MPEG1 Audio 0 packets = 1813, total bytes = 1451520
Video 0 packets = 11879, total bytes = 22211032

>
> I assume that any DVD-PS stream is an incorrect format for SVCD, since the
> SVCD stream specs are not DVD-compliant. So this answer would be no. I don't
> see how it's relevant though, since the PVR250 doesn't output PS streams with
> DVD NAV packets if I understand correctly. I believe it's necessary to remux
> the PS stream to insert the NAV placeholders. And again, no, this should not
> create any audio sync issues.

Although I don't know for sure, I suspect that if there is extra
information (like 0xbf DVD nav streams) that SVCD doesn't know about, it'll
ignore them... so long as the video/audio streams are the right size/rate. The
PVR250s don't output NAV packets, but I don't think they're necessary for DVD
players to play them... just if you want to do fancy things like seamless
jumping, etc.

>
> > There are a few different fundamental goals I can see would be useful for
> > arching mythtv folks:
> >
> > 1. Simple, fast "VCR" functionality... quick and simple recording onto DVD
> > from a PVR-[23]50 set to record in a DVD compatible format. This would
> > preferrably have commercial-cutting ability, but that's all.
> > Advantages: Quick, easy (especially if no commerical cutting),
> > CPU-efficient. Disadvantages: Not the most efficient use of space, can't
> > specify
> > "master-quality" recordings and then "archival-quality" DVD or SVCD since
> > it's recorded/encoded in the final format.
>
> This is basically my own goal. I do it manually now. I don't feel the
> disadvantage as strongly as you imply it to be, since if I really want to
> shrink the size requirements I simply requantize the video instead of
> re-encoding.

I'm a bit of a perfectionist nut, so if I'm going to fry up something,
I want to fill up the disk (with either quality or quantity). I lament the
lack of 2/3 D1 resolution (480x480) on the dvd standard, as 352x480 isn't
broadcast quality and 704x480 is overkill. The SVCD is right in resolution,
but short on space without high-quality encoding. In short, I'm just a nut...
:)

>
> > 2. Efficient/convenient, "Archive" functionality... Recording at
> > high-quality ("Master copy"). Commercial cutting and transcoding in
> > post-processing. This allows for the best quality/bitrate ratio and makes
> > archiving to less expensive media (e.g. SVCD) or more pack more episodes
> > onto DVD's. Especially important for the SVCD/DVD decision, as the
> > resolutions aren't compatible (480x480 for SVCD, 352x480 for DVD, and
> > 704x480 which is gross overkill for cable-quality captures).
>
> Again, I've had good results with tcrequant instead of transcoding or
> re-encoding the whole stream. Some of the archive DVDs I've done of animated
> cartoons (think "Family Guy") requant very well and I've been able to fit 6
> hours or so on a single DVD with good quality.

I've played with tcrequant, and I've been impressed. My foray into
using avidemux is an attempt at streamlining the process (including cuts)...
preferrably without having to strip/crunch/remux. The quality I got from an
1.2 factor tcrequant is noticably less than that from a reencode via avidemux,
though. Thus the multiple "modes" I described in the original email....
different targets require different compromises.

>
> > 3. Space efficient, "Computer archive" functionality. Similar to #2, but
> > with the ultimate goal of MPEG4 archiving on computer media. Once the
> > requirement of set-top box compatibility is removed, anything mplayer can
> > play is valid.
>
> Agreed. Many issues drop away if you aren't targetting playability in common
> set-top DVD players. :)

Of course should set-top boxes play MPEG4's sometime in the future,
life is good... :)

>
> >
> > Did I miss anything? :)
>
> Only things that come to mind right now are:
>
> 4. Instead of burning 1 show per disk, an interface for collecting media-ready
> titles that can be accumulated and selected for burning multiple captures to
> a single disk.

Agreed. I haven't even used nuvexport since the myth box is quite a
PITA to access from the command-line or anything other than the "production"
remote interface (no monitor/keyboard/network).

>
> 5. The obvious menu-generation features that would be welcomed by users of the
> preceeding #4. ;)

Patience... :) I got a DVD burner over a year ago and was quite
dissappointed at the lack of linux DVD software. It has gotten much better
recently, and I think will eventually be quite good. It's a lot to ask of
mythtv to put a nice GUI on a nonexistent (or barely existent) backend toolset.

-Cory

--
*************************************************************************
* The prime directive of Linux: *
* - learn what you don't know, *
* - teach what you do. *
* (Just my 20 USm$) *
*************************************************************************

james at mauibay

Mar 14, 2004, 12:09 PM

Post #22 of 26 (2964 views)
Permalink

Re: Cutting commercials without expensive transcoding [In reply to]

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On Sunday 14 March 2004 4:56 am, papenfuss [at] juneau wrote:
> > > - The hardware encoders don't have the benefit of a 2-pass encoding
> > > scheme (being a causal device and all... :) or high-quality denoising,
> > > so they don't necessarily make the right choices on I/P/B frames all
> > > the time. It makes sense to me that I frames should be used on large
> > > scene changes... but that's not necessarily done with the raw captured
> > > streams and causes wasted bandwidth. For the best quality/bitrate
> > > ratio, post-processing (i.e. *re-encoding*) will be necessary.
> >
> > Re-encoding isn't going to restore quality that isn't there. Also,
> > considering that the quality of the cable TV signal feeding the PVRx50
> > card is much lower than DVD quality to begin with, we're not talking
> > about creating high-quality DVDs, I thought we were talking only about
> > burning some commercial-cut TV shows to a standard format on plastic. ;)
>
> That's quite true, but I'm talking about the best quality/bitrate
> possible. For NTSC captures, anything over 480x480 is wasted resolution.
> If you scale that to typical DVD movie MPEG2 bitrate of 3.5 Mbps, the
> 480x480 shouldn't require more than 2.3 Mbps to obtain the same results.
> The PVR-[23]50's tend to look pretty blocky at such low bitrates. If
> captured at higher bitrate and then cut back, it can look better than if
> captured at low bitrate to start with, since the encoder has the potential
> advantage of 2-pass encoding, etc.

I think you have some misconceptions about the relationship of resolution to
bitrate in MPEG video. MPEG isn't simply compressing pixels, and reducing the
number of pixels doesn't simply reduce the need for bitrate. Regardless, I
understand what you are saying and while it's true that with tweaking you can
get the best possible results by using a 2-pass encoder for the final
version, I personally haven't found it necessary. By the way, what encoder
and switches are you using to encode MPEG2 in 2-pass mode? ;)

> > > - The avidemux program still has some issues with processing streams.
> > > Using the DVD-PS output file type produces DVD-compatible streams that
> > > are much larger than ones manually mux'd with tcmplex. Unfortunately,
> > > extracting (or processing) video and audio streams separately generally
> > > tends to cause sync problems. Also, is a DVD-PS (with NAV packets)
> > > acceptable as an SVCD stream?
> >
> > I don't understand. Manually muxing has nothing to do with file sizes.
> > I've had audio sync issues when capturing to elemental (non-PS) separate
> > streams, but never a problem with the PS streams output by my PVR250's.
> > Demuxing and remuxing my PVR250 streams has never produced any audio sync
> > issues for me at all.
>
> It doesn't seem like it should, but it does. There's much more in a
> DVD mpeg stream that audio and video... and lots of choices that can be
> made. I did the same thing two different ways... a 1 minute clip muxed with
> avidemux's DVD-PS, and the other 'tcmplex -m dvd'. Here are the resulting
> file sizes:
> 21720 test.m2v
> 1428 test.mp2
> 23912 test_tcmplexdvdps.mpg
> 27540 test_avidemuxdvdps.mpg

Wow, I'm surprised. Then again, I've never muxed with avidemux, I only use the
raw video/audio. I also rarely use tcmplex, and usually use mplex.

> So, there's 3% overhead for the tcmplex'd one, and 18% overhead for the
> avidemux'd one. There's lots of padding inserted from avidemux.
>
> The tcmplex'd version shows this from tcscan and vstrip:
> ------------- presentation unit [0] ---------------
> stream id [0xbb] 121
> stream id [0xbe] 123
> stream id [0xbf] 242
> stream id [0xc0] 722
> stream id [0xe0] 11098
> 12306 packetized elementary stream(s) PES packets found
> presentation unit PU [0] contains 121 MPEG video sequence(s)
> Average Bitrate is 5000. Min Bitrate is 5000, max is 5000 (CBR)
>
> Summary:
> MPEG Packs = 11942
> System headers = 121
> Padding packets = 123, total bytes = 129436
> Private 2 packets = 242, total bytes = 241758
> MPEG1 Audio 0 packets = 722, total bytes = 1454500
> Video 0 packets = 11098, total bytes = 22202806
>
> and the avidemux'd one shows:
> ------------- presentation unit [0] ---------------
> stream id [0xbb] 61
> stream id [0xbe] 3621
> stream id [0xbf] 122
> stream id [0xc0] 1813
> stream id [0xe0] 11879
> 17496 packetized elementary stream(s) PES packets found
> presentation unit PU [0] contains 121 MPEG video sequence(s)
> Average Bitrate is 5000. Min Bitrate is 5000, max is 5000 (CBR)
>
> Summary:
> MPEG Packs = 13753
> System headers = 61
> Padding packets = 3621, total bytes = 4031738
> Private 2 packets = 122, total bytes = 121878
> MPEG1 Audio 0 packets = 1813, total bytes = 1451520
> Video 0 packets = 11879, total bytes = 22211032
>
> > I assume that any DVD-PS stream is an incorrect format for SVCD, since
> > the SVCD stream specs are not DVD-compliant. So this answer would be no.
> > I don't see how it's relevant though, since the PVR250 doesn't output PS
> > streams with DVD NAV packets if I understand correctly. I believe it's
> > necessary to remux the PS stream to insert the NAV placeholders. And
> > again, no, this should not create any audio sync issues.
>
> Although I don't know for sure, I suspect that if there is extra
> information (like 0xbf DVD nav streams) that SVCD doesn't know about, it'll
> ignore them... so long as the video/audio streams are the right size/rate.
> The PVR250s don't output NAV packets, but I don't think they're necessary
> for DVD players to play them... just if you want to do fancy things like
> seamless jumping, etc.

Why would you mux with DVD NAV at all for a SVCD target? They are only
placeholders that will be filled in during the DVD authoring process, no?
Without something like dvdauthor to generate the VOBU information and then
stuff relevant information into those placeholders, they are useless. I
didn't know vcdimager would even use a stream that has them. (Never tried.)

> > > There are a few different fundamental goals I can see would be useful
> > > for arching mythtv folks:
> > >
> > > 1. Simple, fast "VCR" functionality... quick and simple recording onto
> > > DVD from a PVR-[23]50 set to record in a DVD compatible format. This
> > > would preferrably have commercial-cutting ability, but that's all.
> > > Advantages: Quick, easy (especially if no commerical cutting),
> > > CPU-efficient. Disadvantages: Not the most efficient use of space,
> > > can't specify
> > > "master-quality" recordings and then "archival-quality" DVD or SVCD
> > > since it's recorded/encoded in the final format.
> >
> > This is basically my own goal. I do it manually now. I don't feel the
> > disadvantage as strongly as you imply it to be, since if I really want to
> > shrink the size requirements I simply requantize the video instead of
> > re-encoding.
>
> I'm a bit of a perfectionist nut, so if I'm going to fry up something,
> I want to fill up the disk (with either quality or quantity). I lament the
> lack of 2/3 D1 resolution (480x480) on the dvd standard, as 352x480 isn't
> broadcast quality and 704x480 is overkill. The SVCD is right in
> resolution, but short on space without high-quality encoding. In short,
> I'm just a nut...
> :)

I'm surprised you don't capture in 704x480 then. :) It may be overkill for the
signal source, but I've had several perfectionists argue to me that it looks
better. My position is that for cable-TV captures, 704x480 looks identical to
352x480 when viewed via an NTSC output device. Resolution has nothing to do
with image quality, as long as it's higher than the signal source. Bitrate is
everything for MPEG2.

> > > 2. Efficient/convenient, "Archive" functionality... Recording at
> > > high-quality ("Master copy"). Commercial cutting and transcoding in
> > > post-processing. This allows for the best quality/bitrate ratio and
> > > makes archiving to less expensive media (e.g. SVCD) or more pack more
> > > episodes onto DVD's. Especially important for the SVCD/DVD decision,
> > > as the resolutions aren't compatible (480x480 for SVCD, 352x480 for
> > > DVD, and 704x480 which is gross overkill for cable-quality captures).
> >
> > Again, I've had good results with tcrequant instead of transcoding or
> > re-encoding the whole stream. Some of the archive DVDs I've done of
> > animated cartoons (think "Family Guy") requant very well and I've been
> > able to fit 6 hours or so on a single DVD with good quality.
>
> I've played with tcrequant, and I've been impressed. My foray into
> using avidemux is an attempt at streamlining the process (including
> cuts)... preferrably without having to strip/crunch/remux. The quality I
> got from an 1.2 factor tcrequant is noticably less than that from a
> reencode via avidemux, though. Thus the multiple "modes" I described in
> the original email.... different targets require different compromises.

Very true. My results with tcrequant are very dependant on the source
material. It's a very hard thing to automate.

> > > 3. Space efficient, "Computer archive" functionality. Similar to #2,
> > > but with the ultimate goal of MPEG4 archiving on computer media. Once
> > > the requirement of set-top box compatibility is removed, anything
> > > mplayer can play is valid.
> >
> > Agreed. Many issues drop away if you aren't targetting playability in
> > common set-top DVD players. :)
>
> Of course should set-top boxes play MPEG4's sometime in the future,
> life is good... :)

Yah. A couple do, but I think it's just playing files on an ISO disk ala the
MP3-playing boxes. I'm not aware of any format that allows for MPEG4 on a DVD
structure, official or otherwise. Yet. Unfortunately, I read something lately
about Microsoft getting one of their proprietary codecs into the next
standard.

> > > Did I miss anything? :)
> >
> > Only things that come to mind right now are:
> >
> > 4. Instead of burning 1 show per disk, an interface for collecting
> > media-ready titles that can be accumulated and selected for burning
> > multiple captures to a single disk.
>
> Agreed. I haven't even used nuvexport since the myth box is quite a
> PITA to access from the command-line or anything other than the
> "production" remote interface (no monitor/keyboard/network).
>
> > 5. The obvious menu-generation features that would be welcomed by users
> > of the preceeding #4. ;)
>
> Patience... :) I got a DVD burner over a year ago and was quite
> dissappointed at the lack of linux DVD software. It has gotten much better
> recently, and I think will eventually be quite good. It's a lot to ask of
> mythtv to put a nice GUI on a nonexistent (or barely existent) backend
> toolset.

I knew things were raw when I got my burner almost 2 years ago. Things are
_way_ better, but not there yet. At least I've been able to make my own
custom menus and limited special features with dvdauthor, though with much
time and effort.

> -Cory
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james at mauibay

Mar 14, 2004, 12:22 PM

Post #23 of 26 (2968 views)
Permalink

Re: Cutting commercials without expensive transcoding [In reply to]

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On Saturday 13 March 2004 2:55 pm, david.blevins [at] visi wrote:
> On Sat, Mar 13, 2004 at 01:23:26PM -1000, James L. Paul wrote:
> > Again, I've had good results with tcrequant instead of transcoding or
> > re-encoding the whole stream. Some of the archive DVDs I've done of
> > animated cartoons (think "Family Guy") requant very well and I've been
> > able to fit 6 hours or so on a single DVD with good quality.
>
> Wow, about 90% of what I capture is cartoons, this would be great for
> me. Can you post some notes on your process?

I don't have anything written up, I just do it by hand each time. I know,
kinda old-school, but I've been using CLI for decades.

Basically, here's what I do (from memory)...

1. Copy the captured nuv file to my main machine
2. Use avidemux2 to cut the nuv into .m2v and .mp2 segments (this is just to
remove commercials, otherwise I just demux the whole thing with tcextract)
3. Shrink each .m2v file with tcrequant as desired
4. Mux the elements together with "mplex -f 8 -V" to get a set of .mpg files
5. Feed those files to dvdauthor to generate a DVD structure
6. Build a DVD ISO image with mkisofs
7. Burn to plastic with cdrecord-prodvd.

> -David
>

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james at mauibay

Mar 14, 2004, 12:31 PM

Post #24 of 26 (2972 views)
Permalink

Re: Cutting commercials without expensive transcoding [In reply to]

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On Saturday 13 March 2004 6:23 pm, Anthony wrote:
> Is there anyway to pass a cutlist to avidemux2? I have looked at the
> commandline parameters in the docs but it doesn't appear that there is a
> way?

I don't think so, but avidemux2 does have a commandline interface. It should
be possible to script specific cuts from a script that reads a cutfile and
invokes avidemux2 for each cut. I think somebody on this list actually had
that automated, although if I remember correctly it was unwieldy because
avidemux2 doesn't provide any way to hide the GUI when called from a
commandline.

FWIW, I haven't tried it.

> --Anthony
>
> > -----Original Message-----
> > From: mythtv-users-bounces [at] mythtv [mailto:mythtv-users-
> > bounces [at] mythtv] On Behalf Of James L. Paul
> > Sent: Saturday, March 13, 2004 1:12 PM
> > To: Discussion about mythtv
> > Subject: Re: [mythtv-users] Cutting commercials without expensive
> > transcoding
> >
> > -----BEGIN PGP SIGNED MESSAGE-----
> > Hash: SHA1
> >
> > On Thursday 11 March 2004 6:22 pm, Len Reed wrote:
> > > Hi,
> > >
> > > I'm no video expert, so maybe I misunderstand the problem. Or maybe
> > > I'm missing a simple answer that's already there.
> > >
> > > I have a PVR250, so my .nuv files are mpeg2 with video and audio
> > > multiplexed in them. After I've marked the commercials (i.e., started
> > > with myth's guesses and tweaked them using the built-in cut editor),
> > > I'd like to do two things:
> > >
> > > 1. Remove the dreaded commercials in order to shrink the file.
> >
> > I also use PVR250 output. I still remove commecials manually with
> > avidemux2
> > when I want to archive to CVD or DVD. I only cut on keyframe boundaries.
> >
> > > and optionally
> > >
> > > 2. convert to a plain mpeg2 for use in burning a DVD. (The issue here
> > > may be my poor DVD authoring s/w. mplayer plays the unmolested .nuv
> > > files. OTOH, mplayer will play almost anything.)
> >
> > This has been discussed on this list, with specific steps. It's very
> > easy. The
> > output of the PVR250 will work fine on a DVD with no transcoding. I just
> > cut
> > out the commercials with avidemux2, remultiplex with DVD nav headers and
> > pass
> > it to dvdauthor. I have burned many DVDs and CVDs from non-transcoded
> > PVR250
> > output captured from my MythTV box. The video format is fine, the audio
> > format seems to work on most DVD players also. (Technically, I think
> > standard
> > players aren't required to play MPEG audio is AC3 audio isn't present,
> > but I
> > haven't heard of a case yet where it doesn't work anyway.)
> >
> > > I've tried using various methods to accomplish #1: the built-in
> > > transcoding (press 'x'), nuvexport, etc. The problem with all of them
> > > is that they do time-consuming transcoding.
> >
> > I'm not aware that anybody has a fully automated process for this from
> > within
> > myth. There are people working on it though.
> >
> > > I don't want to change the bit rate or the format, I just want to lift
> > > the parts that have the actual program, leaving behind the ads. It
> > > seems that that should take, in theory, about as much time as it takes
> > > to read the parts of the original file that I care about and write them
> > > out. No serious computation, though maybe a bit of knitting around the
> > > edges.
> >
> > The basic key to this is to capture in a DVD-compliant stream format in
> > the
> > first place. You should only need to transcode if your captured stream is
> > the
> > wrong resolution or bitrate.
> >
> > > So,
> > >
> > > a. Am I missing something that this makes this far more computationally
> > > intensive than I think?
> >
> > Nope. It's more a matter of automation. We need a tool that can
> > accurately do
> > keyframe edits based on the cutlist, remultiplex the results for
> > dvdauthor,
> > then create and burn a DVD image.
> >
> > > b. Am I missing an existing tool that does what I want?
> >
> > We all are. ;) As is common for open source tools, the building blocks
> > all exist. We simply need to build something polished with them. MythTV
> > is a shining example of this process, and it's still relatively young
> > yet.
> >
> > > Thanks,
> > > Len
> >
> > -----BEGIN PGP SIGNATURE-----
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> >
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> > jMksFwmCoK+zFIydGN2Eu+I=
> > =79wi
> > -----END PGP SIGNATURE-----
> > _______________________________________________
> > mythtv-users mailing list
> > mythtv-users [at] mythtv
> > http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users
>
> !DSPAM:4053f31e111121715812429!
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papenfuss at juneau

Mar 14, 2004, 2:01 PM

Post #25 of 26 (2964 views)
Permalink

Re: Cutting commercials without expensive transcoding [In reply to]

> > That's quite true, but I'm talking about the best quality/bitrate
> > possible. For NTSC captures, anything over 480x480 is wasted resolution.
> > If you scale that to typical DVD movie MPEG2 bitrate of 3.5 Mbps, the
> > 480x480 shouldn't require more than 2.3 Mbps to obtain the same results.
> > The PVR-[23]50's tend to look pretty blocky at such low bitrates. If
> > captured at higher bitrate and then cut back, it can look better than if
> > captured at low bitrate to start with, since the encoder has the potential
> > advantage of 2-pass encoding, etc.
>
> I think you have some misconceptions about the relationship of resolution to
> bitrate in MPEG video. MPEG isn't simply compressing pixels, and reducing the
> number of pixels doesn't simply reduce the need for bitrate. Regardless, I
> understand what you are saying and while it's true that with tweaking you can
> get the best possible results by using a 2-pass encoder for the final
> version, I personally haven't found it necessary. By the way, what encoder
> and switches are you using to encode MPEG2 in 2-pass mode? ;)

Not so, although it may have come across that way. My point is that
everything else being equal, double the number of pixels requires roughly
double the bitrate. I know there are groups of pixels, 16x16 and whatever....
but think of that has having to encode more of the groups of pixels (i.e. more
data to mess with). Now, that said, the resolution/bitrate issue is a bit
complicated with MPEG, but suffice it to say that higher resolution requires a
commensurate increase in bitrate to avoid MPEG artifacts (blockiness, etc). So
for efficiency, there's no point in having to encode artificially contructed
(read: oversampled) data that's not really there.

> > It doesn't seem like it should, but it does. There's much more in a
> > DVD mpeg stream that audio and video... and lots of choices that can be
> > made. I did the same thing two different ways... a 1 minute clip muxed with
> > avidemux's DVD-PS, and the other 'tcmplex -m dvd'. Here are the resulting
> > file sizes:
> > 21720 test.m2v
> > 1428 test.mp2
> > 23912 test_tcmplexdvdps.mpg
> > 27540 test_avidemuxdvdps.mpg
>
> Wow, I'm surprised. Then again, I've never muxed with avidemux, I only use the
> raw video/audio. I also rarely use tcmplex, and usually use mplex.

I was trying to avoid separating the video/audio streams and remuxing
for fear of sync problems (bad past experiences). The tcmplex thing is a
preference I obtained from one of the many HOWTO's I've read recently... don't
really care either way.

> Why would you mux with DVD NAV at all for a SVCD target? They are only
> placeholders that will be filled in during the DVD authoring process, no?
> Without something like dvdauthor to generate the VOBU information and then
> stuff relevant information into those placeholders, they are useless. I
> didn't know vcdimager would even use a stream that has them. (Never tried.)
>
Again... just to get avidemux2 to spit out a mux'd MPEG-PS, rather
than an AVI (which it prefers).

> > I'm just a nut...
> > :)
>
> I'm surprised you don't capture in 704x480 then. :) It may be overkill for the
> signal source, but I've had several perfectionists argue to me that it looks
> better. My position is that for cable-TV captures, 704x480 looks identical to
> 352x480 when viewed via an NTSC output device. Resolution has nothing to do
> with image quality, as long as it's higher than the signal source. Bitrate is
> everything for MPEG2.

Mainly disk space. Believe me... you don't want to get me going on the
resolution thing. That was last month's tangent. I've got some really good
test signal generating software and hardware now though... :) Bottom line is
my PVR-250 has softness of the picture that renders anything about 450 lines
wasted... even though the TV can distinguish about 550 lines. I can, however,
see a difference in the capture quality between 352x480 and 480x480... thus the
desire to capture higher than 352x480. The jump to 704x480 is just too big.

Although, I've recenting been thinking about a hybrid resolution
solution... similar to the anamorphic widescreen idea. If you look at the
default DVD VFilter in avidemux, it wants to rescale a 480x480 4:3 to 540x480
and then pad with black to 720x480. Most DVD players (I've seen anyway) have
the Pan/Scan mode, which stretches the image to fit both horizonatlly and
vertically. If one were to scale a 4:3 (1.33) capture to 540x480 (1.125)
padded with black bars on the *sides* to 720x480 (1.5), it could be watched in
Pan/Scan mode on a DVD player and would look correct. It would be full-screen
on a 4:3, as the black bars on the side would be off the screen. The black
bars wouldn't cost much bitrate to encode, and the 720x480 would then be a
standard DVD size. Anyway, to truly make this friendly, it would have to be
done on the card... i.e. possibly impossible driver hacking. Just a thought
though...

> Very true. My results with tcrequant are very dependant on the source
> material. It's a very hard thing to automate.

Agreed. Not that it necessarily has to be, but I've yet to find
something that ties it all together.

> > Of course should set-top boxes play MPEG4's sometime in the future,
> > life is good... :)
>
> Yah. A couple do, but I think it's just playing files on an ISO disk ala the
> MP3-playing boxes. I'm not aware of any format that allows for MPEG4 on a DVD
> structure, official or otherwise. Yet. Unfortunately, I read something lately
> about Microsoft getting one of their proprietary codecs into the next
> standard.

I figured they'd want to keep hold of the standard. Next thing you
know, all next-gen DVD players will have to run WindersCE to be
"standards"-complient ... :)

> I knew things were raw when I got my burner almost 2 years ago. Things are
> _way_ better, but not there yet. At least I've been able to make my own
> custom menus and limited special features with dvdauthor, though with much
> time and effort.

No kidding.... right now still not worth the trouble for the most part.

-Cory
--
*************************************************************************
* The prime directive of Linux: *
* - learn what you don't know, *
* - teach what you do. *
* (Just my 20 USm$) *
*************************************************************************

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