Mailing List Archive: MythTV: Users

Newbie questions

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thomas at boerkel

Feb 4, 2004, 2:30 AM

Post #1 of 9 (1153 views)
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Newbie questions

HI!

I am planning on building a MythTV box shortly. I have read the hardware
comments in the docs and also a bit through the list archives, but I
have still some questions.

This is what I want to be able to do:
1. record 2 shows at the same time
2. if possible, watch one of those or an older recording at the same time

2. is not a must, but would be nice to have.

As hardware, I could think of:
- P3/866
- 1x PVR-250, 1x PVR-350
- Soundblaster card
- some cheap VGA card

or

- Celeron 2.4 GHz
- 2x PVR-250
- onboard Audio
- NVideo GeForce with TV-out

Would both hardware constellation be OK for my requirements?

I have read, that the PVR-350's MPEG2 decoder output has some
"limitations". What are they?

Is it OK to only have one hard disk (100 GB UDMA/100 Western Digital)?

Should the hard disk have 7200 rpm?

What filesystem should I use? Is reiserFs OK?

If recording from analog TV, what bitrate do I need to get an MPEG2 that
is almost identical to the source? Thinking of the noisyness of analog
TV, I could think about 6 MBit or something.

Thanks!

Thomas

paul_woodward at fastnet

Feb 4, 2004, 2:48 AM

Post #2 of 9 (1111 views)
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Re: Newbie questions [In reply to]

> 1. record 2 shows at the same time
Yes if you have 2 tuners.

> 2. if possible, watch one of those or an older recording at the same time
Absolutely, so long as your processor can take the strain.

>
> 2. is not a must, but would be nice to have.
>
> As hardware, I could think of:
> - P3/866
> - 1x PVR-250, 1x PVR-350
> - Soundblaster card
> - some cheap VGA card
>
> or
>
> - Celeron 2.4 GHz
> - 2x PVR-250
> - onboard Audio
> - NVideo GeForce with TV-out
>
> Would both hardware constellation be OK for my requirements?
Can't advise you on the hardware spec. I run a P2.4C, with 2x DVB cards and can quite happily watch old recordings while it records from 2 cards at once.

>
>
> I have read, that the PVR-350's MPEG2 decoder output has some
> "limitations". What are they?
>
> Is it OK to only have one hard disk (100 GB UDMA/100 Western Digital)?
Yes, but it may fill up fast - I thought 160Gb would last forever - now I have 440Gb.
>
> Should the hard disk have 7200 rpm?
That depends how much you want to do at once. Remember that when watching live TV it is buffered to the HD so that's a read and a write stream, so any additional recordings you make concurrently must also access the HD. I would suggest it, although watch out because they generate a lot of heat and generally you want to keep fans to a minmum in a HTPC. I have 3x 7200's and I'm going to have to shift them to a new box because of the heat.
>
> What filesystem should I use? Is reiserFs OK?
I use ext3, but I've heard good things about reiser - I'll let someone more knowledgeable answer.

> If recording from analog TV, what bitrate do I need to get an MPEG2 that
> is almost identical to the source? Thinking of the noisyness of analog
> TV, I could think about 6 MBit or something.
As above.

HTH, Paul

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cattin at vision

Feb 4, 2004, 3:03 AM

Post #3 of 9 (1126 views)
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Re: Newbie questions [In reply to]

Thomas,

> This is what I want to be able to do:
> 1. record 2 shows at the same time

you need at least two tv-capture cards to do that (as in your HW
configuration)

> 2. if possible, watch one of those or an older recording at the same time

no problem at all. even with one capture card you are able to watch an
older recording while recording a new one.

> Is it OK to only have one hard disk (100 GB UDMA/100 Western Digital)?
> Should the hard disk have 7200 rpm?

just about any harddisk is fast enough.

> What filesystem should I use? Is reiserFs OK?

reiser is perfectly okay. however, I use ext3 (just for personal taste).

> If recording from analog TV, what bitrate do I need to get an MPEG2 that
> is almost identical to the source? Thinking of the noisyness of analog
> TV, I could think about 6 MBit or something.

sounds reasonable. When I tried 4Mbit the image looked blocky during
fast scene-changes.

Philippe

ke-aa at frisurf

Feb 4, 2004, 3:38 AM

Post #4 of 9 (1097 views)
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RE: Newbie questions [In reply to]

Hi,

Paul Woodward wrote:
> Thomas B�rkel wrote:
> > As hardware, I could think of:
> > - P3/866
> > - 1x PVR-250, 1x PVR-350
> > - Soundblaster card
> > - some cheap VGA card

Get this, for killer tv output quality!

You might be limited to outputing mpeg2 only for a little while,
untill the ivtv frambuffer thing gets sorted out.

> > Would both hardware constellation be OK for my requirements?
> Can't advise you on the hardware spec. I run a P2.4C, with 2x
> DVB cards and can quite happily watch old recordings while it
> records from 2 cards at once.

Yea, would be very much ok. The second setup might be better
if you play a lot of other formats than mpeg2, like divx,
but tv out is lacking on the geforce compared to pvr-350.

> > I have read, that the PVR-350's MPEG2 decoder output has some
> > "limitations". What are they?

I belive this limitation is reffering to the actual format of
the mpeg2 stream (profile).

> > What filesystem should I use? Is reiserFs OK?
> I use ext3, but I've heard good things about reiser - I'll
> let someone more knowledgeable answer.

I use ext2 for speed, however recently there has been alot of
power-outs here (because of all the snow), so i've switched
to the ext3 model for the benefit of quick filesystem check
when the system goes down unintentionally. I'll switch back
when all the snow is gone :) Basically you get an overhead
with the journal (although I bet we could argue back and
forth about this for ages).

For more, search the gossamer archive for 'filesystem':
http://www.gossamer-threads.com/archive/MythTV_C2/Dev_F10/

> > If recording from analog TV, what bitrate do I need to get
> > an MPEG2 that is almost identical to the source?
> > Thinking of the noisyness of analog TV,
> > I could think about 6 MBit or something.

I belive this is also answered in the archive, but yea,
experimenting with values around that you are suggesting
is a good start.

Good luck,
Kenneth

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debian at nc

Feb 4, 2004, 5:57 AM

Post #5 of 9 (1124 views)
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Re: Newbie questions [In reply to]

On Wed, 2004-02-04 at 04:30, Thomas B�rkel wrote:
> HI!
>
> I am planning on building a MythTV box shortly. I have read the hardware
> comments in the docs and also a bit through the list archives, but I
> have still some questions.
>
> This is what I want to be able to do:
> 1. record 2 shows at the same time
> 2. if possible, watch one of those or an older recording at the same time
>
> 2. is not a must, but would be nice to have.
>
> As hardware, I could think of:
> - P3/866
> - 1x PVR-250, 1x PVR-350
> - Soundblaster card
> - some cheap VGA card
>
This is my setup except for I have an Athlon. It rarely goes past 5%
usage while recording two shows and watching an old recording. That's
the beauty of the pvr-?50.

> or
>
> - Celeron 2.4 GHz
> - 2x PVR-250
> - onboard Audio
> - NVideo GeForce with TV-out
>
And this is what I had before (except only one 250). Tv-out off the 350
is MUCH better.

> Would both hardware constellation be OK for my requirements?
>
>
> I have read, that the PVR-350's MPEG2 decoder output has some
> "limitations". What are they?
>

Right now you can't use the 350's tv-out for DVD playing, game playing,
or mythvideo. It is my belief that the people at ivtv are working on
the dvd and the video parts...

> Is it OK to only have one hard disk (100 GB UDMA/100 Western Digital)?
>
It's ok but you'll fill it up. (2.2 Gigs / hr. show)

> Should the hard disk have 7200 rpm?
>
I don't think the speed will be a problem until you get to three or four
pvr cards.

> What filesystem should I use? Is reiserFs OK?
>
I use ext3. IMHO they all will work fine.

> If recording from analog TV, what bitrate do I need to get an MPEG2 that
> is almost identical to the source? Thinking of the noisyness of analog
> TV, I could think about 6 MBit or something.
>
Got me there.

> Thanks!
>
> Thomas
>
>
-jose-

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thomas at boerkel

Feb 4, 2004, 6:39 AM

Post #6 of 9 (1123 views)
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Re: Newbie questions [In reply to]

HI!

jose rubio wrote:

>>I have read, that the PVR-350's MPEG2 decoder output has some
>>"limitations". What are they?
>
> Right now you can't use the 350's tv-out for DVD playing, game playing,
> or mythvideo. It is my belief that the people at ivtv are working on
> the dvd and the video parts...

What about MythWeb?

Can I use the PVR-350 TV-out for watching recording and the GeForce
TV-out for games etc.?

> It's ok but you'll fill it up. (2.2 Gigs / hr. show)

Is the recorded video directly burnable to DVD?

>>If recording from analog TV, what bitrate do I need to get an MPEG2 that
>>is almost identical to the source? Thinking of the noisyness of analog
>>TV, I could think about 6 MBit or something.
>>
>
> Got me there.

With 2.2 GB/hr, you will have less. I think 6 MBit is more like 2.8 GB/hr).

Does it look the same as live TV if you are recording with 2.2 GB/hr?

Thomas

steve at nexusuk

Feb 4, 2004, 6:51 AM

Post #7 of 9 (1121 views)
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Re: Newbie questions [In reply to]

On Wed, 4 Feb 2004, Paul Woodward wrote:

> > Should the hard disk have 7200 rpm?
> That depends how much you want to do at once. Remember that when
> watching live TV it is buffered to the HD so that's a read and a write
> stream, so any additional recordings you make concurrently must also
> access the HD. I would suggest it, although watch out because they
> generate a lot of heat and generally you want to keep fans to a minmum
> in a HTPC. I have 3x 7200's and I'm going to have to shift them to a
> new box because of the heat.

I'm unsure if 7200rpm drives are actually needed - I use a 7200rpm drive,
but when you actually add up the datarates of everything, it doesn't
actually add up to a huge number (lets say you record at 6Mbps, 2
recorders and 1 player at the same time come to only 18Mbps).. Similarly
I wouldn't expect seek times to have much impact... avoiding the use of
7200rpm drives would reduce heat a noise quite considerably.

BTW, does anyone know where I can get rubber drive mounts?

> I use ext3, but I've heard good things about reiser - I'll let someone
> more knowledgeable answer.

We've used reiserfs on the servers we sell at work (nothing myth related)
and have had some minor issues with corruption sometimes if the box is
powered off without cleanly unmounting (the contents of one file appearing
inside another file, etc). No real experience of ext3 under similar
conditions, but remember that your average customer puts a server through
a hell of a lot of abuse so it's not that supprising we've had some
problems with the FS :)

--

- Steve http://www.nexusuk.org/

Servatis a periculum, servatis a maleficum - Whisper, Evanescence

atd7 at cornell

Feb 4, 2004, 9:09 AM

Post #8 of 9 (1127 views)
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Re: Newbie questions [In reply to]

Quoting "Philippe C. Cattin" <cattin [at] vision>:

> > Is it OK to only have one hard disk (100 GB UDMA/100 Western Digital)?
> > Should the hard disk have 7200 rpm?
>
> just about any harddisk is fast enough.
Exception: Don't use an external Firewire hard drive. The Linux SBP2 driver
has some *serious* performance issues. It's OK for straight reads or straight
writes, but as soon as you do simultaneous reads/writes, kernel CPU usage spikes
to 100% and transfer rate goes down by a magnitude of order.

Windows doesn't seem to be affected as severely in this regard.

Since I moved to an internal 200GB Seagate 7200RPM drive (The $99 CompUSA deal
that came up a few weeks ago), everything is great though.

> > If recording from analog TV, what bitrate do I need to get an MPEG2 that
> > is almost identical to the source? Thinking of the noisyness of analog
> > TV, I could think about 6 MBit or something.
>
> sounds reasonable. When I tried 4Mbit the image looked blocky during
> fast scene-changes.
Depends on exactly how noisy.
I use 6-7 mbit VBR and the quality is excellent for most channels, but two
channels in my area are just so noisy that the encoder chokes on them no matter
what the bitrate. If you're using analog cable, you should be absolutely fine
though. My problems are when recording weak OTA channels.

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atd7 at cornell

Feb 4, 2004, 9:15 AM

Post #9 of 9 (1111 views)
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Re: Newbie questions [In reply to]

Quoting Thomas B�rkel <thomas [at] boerkel>:

> HI!
>
> jose rubio wrote:
>
> >>I have read, that the PVR-350's MPEG2 decoder output has some
> >>"limitations". What are they?
> >
> > Right now you can't use the 350's tv-out for DVD playing, game playing,
> > or mythvideo. It is my belief that the people at ivtv are working on
> > the dvd and the video parts...
>
> What about MythWeb?
>
> Can I use the PVR-350 TV-out for watching recording and the GeForce
> TV-out for games etc.?
Probably. You might want to investigate an external scan converter. Various
external converters have received good reviews so far, the most anticipated one
is being designed by a guy on this list, it's very cheap and simple. Set the
video card to output interlaced NTSC/PAL timings for its video, and an Analog
Devices AD724 does the rest of the work in converting RGB to NTSC/PAL. Doesn't
work with NVidia's current drivers though, for some reason the current NV
drivers don't like interlaced video modes.

> > It's ok but you'll fill it up. (2.2 Gigs / hr. show)
>
> Is the recorded video directly burnable to DVD?
Not quite. It needs to be remultiplexed. Good news is that it does NOT have to
be reencoded, remultiplexing is a fast operation that is typically I/O bound,
not CPU bound.

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