Mailing List Archive: MythTV: Users

HD PVR: What does "13.5 Mbps" mean?

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ylee at pobox

Apr 4, 2008, 10:31 PM

Post #1 of 7 (2882 views)
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HD PVR: What does "13.5 Mbps" mean?

We'd heard back in January that the Hauppauge HD PVR device allegedly
could handle up to 25Mbps and so could encode 1080p (Blu-ray) video.
However, the description now claims "up to 1080i," and in the official
specifications
(<URL:http://www.hauppauge.com/site/products/hd_pvr.html>), we see

# Hardware encoder
* H.264 AVCHD video encoder
* Datarates from 1Mbit/sec to 13.5 Mbits/sec

What could these datarates mean in this case? The maximum bitrate of
the component-input video it accepts, or the maximum bitrate of the
h.264 files it spits out? If the former, what does this imply about
the device's ability to properly capture the full breadth of 1080i
19.39Mbps input?[1] If the latter, is a 13.5Mbps h.264 recording
really sufficient to capture the full quality of 19.39Mbps MPEG-2?[2]

[1] I don't have a Blu-ray player so all I need is 1080i.
[2] I am told that h.264's vaunted efficiency versus MPEG-2 is mainly
at lower bitrates, and that the relative efficiency decreases
significantly at higher bitrates, to something like only 25% better.

--
Frontend: P4 3.0GHz, 1.5TB software RAID 5 array
Backend: Quad-core Xeon 1.6GHz, 6.6TB sw RAID 6
Video inputs: Four high-definition over FireWire/OTA
Accessories: 47" 1080p LCD, 5.1 digital, and MX-600
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brian.phillips at gmx

Apr 4, 2008, 10:45 PM

Post #2 of 7 (2839 views)
Permalink

Re: HD PVR: What does "13.5 Mbps" mean? [In reply to]

Yeechang Lee wrote:
> We'd heard back in January that the Hauppauge HD PVR device allegedly
> could handle up to 25Mbps and so could encode 1080p (Blu-ray) video.
> However, the description now claims "up to 1080i," and in the
> official specifications
> (<URL:http://www.hauppauge.com/site/products/hd_pvr.html>), we see
>
> # Hardware encoder
> * H.264 AVCHD video encoder
> * Datarates from 1Mbit/sec to 13.5 Mbits/sec
>
> What could these datarates mean in this case? The maximum bitrate of
> the component-input video it accepts, or the maximum bitrate of the
> h.264 files it spits out? If the former, what does this imply about
> the device's ability to properly capture the full breadth of 1080i
> 19.39Mbps input?[1] If the latter, is a 13.5Mbps h.264 recording
> really sufficient to capture the full quality of 19.39Mbps MPEG-2?[2]
>
> [1] I don't have a Blu-ray player so all I need is 1080i.
> [2] I am told that h.264's vaunted efficiency versus MPEG-2 is mainly
> at lower bitrates, and that the relative efficiency decreases
> significantly at higher bitrates, to something like only 25% better.

Since component is analog, there is no "bitrate" associated with it. It
would have to be the h.264 being pumped out of the box. As for the quality
of that signal... I dunno.

Brian

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willyboyd at gmail

Apr 5, 2008, 7:36 AM

Post #3 of 7 (2783 views)
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Re: HD PVR: What does "13.5 Mbps" mean? [In reply to]

On Sat, Apr 5, 2008 at 12:31 AM, Yeechang Lee <ylee [at] pobox> wrote:
[snip]
> h.264 files it spits out? If the former, what does this imply about
> the device's ability to properly capture the full breadth of 1080i
> 19.39Mbps input?[1] If the latter, is a 13.5Mbps h.264 recording
> really sufficient to capture the full quality of 19.39Mbps MPEG-2?[2]
[snip]

I've always thought that any recompression is never really sufficient
to capture the full quality of the source. However, h.264 usually
carries the same quality at lower bitrates, so I could see 13.5Mbps
still looking very good for anything coming out of your cable box.
I'm not sure how bad that would compare to Bluray source, as I don't
own a player yet.

- Willy
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mitchell.gore at gmail

Apr 5, 2008, 7:50 AM

Post #4 of 7 (2802 views)
Permalink

Re: HD PVR: What does "13.5 Mbps" mean? [In reply to]

On Sat, Apr 5, 2008 at 12:45 AM, Brian Phillips <brian.phillips [at] gmx>
wrote:

> Yeechang Lee wrote:
> > We'd heard back in January that the Hauppauge HD PVR device allegedly
> > could handle up to 25Mbps and so could encode 1080p (Blu-ray) video.
> > However, the description now claims "up to 1080i," and in the
> > official specifications
> > (<URL:http://www.hauppauge.com/site/products/hd_pvr.html>), we see
> >
> > # Hardware encoder
> > * H.264 AVCHD video encoder
> > * Datarates from 1Mbit/sec to 13.5 Mbits/sec
> >
> > What could these datarates mean in this case? The maximum bitrate of
> > the component-input video it accepts, or the maximum bitrate of the
> > h.264 files it spits out? If the former, what does this imply about
> > the device's ability to properly capture the full breadth of 1080i
> > 19.39Mbps input?[1] If the latter, is a 13.5Mbps h.264 recording
> > really sufficient to capture the full quality of 19.39Mbps MPEG-2?[2]
> >
> > [1] I don't have a Blu-ray player so all I need is 1080i.
> > [2] I am told that h.264's vaunted efficiency versus MPEG-2 is mainly
> > at lower bitrates, and that the relative efficiency decreases
> > significantly at higher bitrates, to something like only 25% better.
>
> Since component is analog, there is no "bitrate" associated with it. It
> would have to be the h.264 being pumped out of the box. As for the
> quality
> of that signal... I dunno.
>
> Brian
>
> _______________________________________________
>

I would also like to know, once we get Linux drivers, how beefy of a CPU is
required. The specs from Hauppauge says a dual core but in Windows can get
away with lower CPU as it does video card offload. What will be a
requirement for this? Are the apple video 1080p trailers comparable? I'm
just hoping my AMD X2 5700 (dual core 2.7ghz) will be able to keep up.

One huge disadvantage of this devices (thanks to nvidia) is our miniumum CPU
requirements will go up AGAIN! Unless Nvidia ever blesses up with h.246
offload in XvMC.

Mitchell

masterclc at gmail

Apr 5, 2008, 8:47 AM

Post #5 of 7 (2778 views)
Permalink

Re: HD PVR: What does "13.5 Mbps" mean? [In reply to]

> I would also like to know, once we get Linux drivers, how beefy of a CPU is
> required. The specs from Hauppauge says a dual core but in Windows can get
> away with lower CPU as it does video card offload. What will be a
> requirement for this? Are the apple video 1080p trailers comparable? I'm
> just hoping my AMD X2 5700 (dual core 2.7ghz) will be able to keep up.

The apple video trailers are somewhat comparable, but they aren't
"maximum" so it isn't a good means of testing out the theoretical
maximum your system can do.

> One huge disadvantage of this devices (thanks to nvidia) is our miniumum CPU
> requirements will go up AGAIN! Unless Nvidia ever blesses up with h.246
> offload in XvMC.
>
> Mitchell

This is really why it's so nice (and very important) to keep your eye
on Intel. They are working on this type of acceleration with their
integrated chipsets. We will have an open-source vendor creating open
source drivers that work with our new h.264 media; that is better than
just about anything Nvidia can currently offer me.

-Chad
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jedi at mishnet

Apr 5, 2008, 5:29 PM

Post #6 of 7 (2776 views)
Permalink

Re: HD PVR: What does "13.5 Mbps" mean? [In reply to]

On Sat, Apr 05, 2008 at 09:47:39AM -0600, Chad wrote:
> > I would also like to know, once we get Linux drivers, how beefy of a CPU is
> > required. The specs from Hauppauge says a dual core but in Windows can get
> > away with lower CPU as it does video card offload. What will be a
> > requirement for this? Are the apple video 1080p trailers comparable? I'm
> > just hoping my AMD X2 5700 (dual core 2.7ghz) will be able to keep up.
>
> The apple video trailers are somewhat comparable, but they aren't
> "maximum" so it isn't a good means of testing out the theoretical
> maximum your system can do.

OTOH, it represents a potentially useful transcoding target. If
the HD-PVR is flexible enough (much like a PVR150) can be, perhaps
it can be configured to avoid this problem.

>
> > One huge disadvantage of this devices (thanks to nvidia) is our miniumum CPU
> > requirements will go up AGAIN! Unless Nvidia ever blesses up with h.246
> > offload in XvMC.
> >
> > Mitchell
>
> This is really why it's so nice (and very important) to keep your eye
> on Intel. They are working on this type of acceleration with their
> integrated chipsets. We will have an open-source vendor creating open
> source drivers that work with our new h.264 media; that is better than
> just about anything Nvidia can currently offer me.

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adeffs.mythtv at gmail

Apr 7, 2008, 11:00 AM

Post #7 of 7 (2724 views)
Permalink

Re: HD PVR: What does "13.5 Mbps" mean? [In reply to]

On Sat, Apr 5, 2008 at 10:36 AM, Willy Boyd <willyboyd [at] gmail> wrote:
> On Sat, Apr 5, 2008 at 12:31 AM, Yeechang Lee <ylee [at] pobox> wrote:
> [snip]
>
> > h.264 files it spits out? If the former, what does this imply about
> > the device's ability to properly capture the full breadth of 1080i
> > 19.39Mbps input?[1] If the latter, is a 13.5Mbps h.264 recording
> > really sufficient to capture the full quality of 19.39Mbps MPEG-2?[2]
> [snip]
>
> I've always thought that any recompression is never really sufficient
> to capture the full quality of the source. However, h.264 usually
> carries the same quality at lower bitrates, so I could see 13.5Mbps
> still looking very good for anything coming out of your cable box.
> I'm not sure how bad that would compare to Bluray source, as I don't
> own a player yet.

except that BluRay/HD-DVD are h264 to begin with, and like the OP
pointed out, at a much higher bitrate. BUT also remember that
broadcast HDTV is currently MPEG2, so the color depth is much lower
than BluRay and the compression level is "higher" (different really,
but basically less bits per pixel are reserved than on the h264 used
for BluRay).

So the bitrate for h264 used by the HDPVR is more than sufficient to
get very very close to the quality level of the original broadcast,
though, of course, due to the D->A->D steps required, won't be as good
as capturing via QAM or Firewire (which is just capturing the original
MPEG2 stream).

--
Steve
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