Mailing List Archive: RE: A noob question regarding hardware req. and hardwarecodecs

RE: A noob question regarding hardware req. and hardwarecodecs

Aug 5, 2003, 10:09 AM

Post #1 of 10 (2191 views)

Comments inline.

> -----Original Message-----
> From: mythtv-users-bounces@mythtv.org
> [mailto:mythtv-users-bounces@mythtv.org]On Behalf Of John Wells
> Sent: Tuesday, August 05, 2003 12:32 PM
> To: mythtv-users@mythtv.org
> Subject: [mythtv-users] A noob question regarding hardware req. and
> hardwarecodecs
>
>
> Hi guys. New to the list and MythTV and have a few questions, if you
> don't mind.
>
> Here's what I'd like to do with my Freevo or MythTV PVR:
>
> R.1 - Watch live tv while recording another show on another channel
> R.2 - Watch live tv while recording the currently viewed show.
> R.3 - Pause live tv.
>
> Here's what I have regarding hardware so far:
> - ATI Tv-wonder tuner card (w/stereo)
> - Geforce 2 with S-video out
> - 256 mb ram
> - 40 gb harddrive
> - CD-RW
>
> Now here's where I'm a little unsure of what to get next. I have a AMD
> Athlon XP 2200+ I can throw at this baby, but I'd hate to use my big mean
> system for a PVR if I don't have to. My other option is to buy a system
> from e-bay, but my $$$ range dictates (based on current prices out there)
> that the fastest I'll be able to buy will probably be around a PIII-500
> (give or take a 100) Mhz.
>
> Now the questions:
>
> 1. Will a 500 Mhz CPU suffice for what I'd like to do, or will I really
> have to go with the 2200? I'd like at least regular TV quality video (but
> truthfully, it'll probably bug me if I don't have the best ;-))

Probably not with your current hardware. Possibly with a hardware encoder
(see below).
General rule of thumb: ~1GHz per encoding stream, + at ~500MHz for playback.
I've got an Athlon XP 1600+ handling a single V4L tuner, which is just about
enough power. It'd be nice to have a little more breathing room, though. I
definitely couldn't handle 2 V4L tuners without *really* sacrificing
quality.

> 2. If I buy a hardware encoder like the Haupauge 250 or 350, what sort of
> effect will that have on CPU requirements? Assuming a purchase of one of
> those cards, what CPU could I get buy with?

A hardware MPEG encoder reduces the encoding load on your processor to
virtually nothing. Thus, with such a setup you really only need a system
that can handle full screen MPEG-2 decoding & playback. A PIII-500 might be
OK there.

> 3. Do I have to buy a second tuner card to be able to record one channel
> while watching live tv on another (See R.1 above)?

Yes.

> 4. Can a MythTV system be used for other things (i.e., can I drop out to
> an X session), or does the software pretty much need a dedicated machine?

The frontend (user interface) is separate from the backend (interface to the
tuner card, scheduler, etc), so it's quite possible to quit the frontend and
use your machine for other things. Keep in mind that if your system doesn't
have a lot of spare CPU, doing things like compiling while the backend is
recording something could cause dropped frames/stuttering recordings. The
backend needs always to be running if you want to record scheduled programs.

> 5. Is there any way to get MythTV to communicate with my Comcast digital
> cable box so that I can take advantage of the extra channels?

Depending on the model of your cable box, you can control it with either a
serial cable or an IR transmitter. Search the list archives for specifics.

-JAC

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RE: A noob question regarding hardware req. andhardwarecodecs [ In reply to ]

jb at sourceillustrated

Aug 5, 2003, 10:31 AM

Post #2 of 10 (2171 views)

Permalink

Joseph:

Joseph A. Caputo said:
> Probably not with your current hardware. Possibly with a hardware encoder
> (see below).
> General rule of thumb: ~1GHz per encoding stream, + at ~500MHz for
> playback.
> I've got an Athlon XP 1600+ handling a single V4L tuner, which is just
> about
> enough power. It'd be nice to have a little more breathing room, though.
> I
> definitely couldn't handle 2 V4L tuners without *really* sacrificing
> quality.
>
>> 2. If I buy a hardware encoder like the Haupauge 250 or 350, what sort
>> of
>> effect will that have on CPU requirements? Assuming a purchase of one
>> of
>> those cards, what CPU could I get buy with?
>
> A hardware MPEG encoder reduces the encoding load on your processor to
> virtually nothing. Thus, with such a setup you really only need a system
> that can handle full screen MPEG-2 decoding & playback. A PIII-500 might
> be
> OK there.

Based on your above comments, and based on what I have now, if I buy a
Hauppauge PVR-250 or 350 and use the current ATI TV wonder as my second
tuner, am I correct in assuming that having only one PVR-250/350 will
force me to still have at least a 1 GHZ processor for recording and
watching live tv at the same time?

Thanks for your input!

John

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RE: A noob question regarding hardware req. andhardwarecodecs [ In reply to ]

ScottB at Cavps

Aug 5, 2003, 10:39 AM

Post #3 of 10 (2162 views)

Permalink

You are correct.
Formula:
Decoding: 500Mhz per stream (usually just one)
Software Encoding: 1000Mhz per stream
Hardware Encoding: 200Mhz per stream

So for a combined front-end/back-end with one pvr-250 tuner and one V4L
tuner you'd be looking at 500Mhz + 1000Mhz + 200Mhz = 1700Mhz

These numbers do assume intel CPU though. For AMD, use the XP rating and
add 100 or so. (I.e. use an Athlon XP1800+ instead of Atlhon XP1700+)

Hope this helps.

-----Original Message-----
From: John Wells [mailto:jb@sourceillustrated.com]
Sent: Tuesday, August 05, 2003 12:32 PM
To: Discussion about mythtv
Cc: Discussion about mythtv
Subject: RE: [mythtv-users] A noob question regarding hardware req.
andhardwarecodecs

Joseph:

Joseph A. Caputo said:
> Probably not with your current hardware. Possibly with a hardware
encoder
> (see below).
> General rule of thumb: ~1GHz per encoding stream, + at ~500MHz for
> playback.
> I've got an Athlon XP 1600+ handling a single V4L tuner, which is just
> about
> enough power. It'd be nice to have a little more breathing room,
though.
> I
> definitely couldn't handle 2 V4L tuners without *really* sacrificing
> quality.
>
>> 2. If I buy a hardware encoder like the Haupauge 250 or 350, what
sort
>> of
>> effect will that have on CPU requirements? Assuming a purchase of
one
>> of
>> those cards, what CPU could I get buy with?
>
> A hardware MPEG encoder reduces the encoding load on your processor to
> virtually nothing. Thus, with such a setup you really only need a
system
> that can handle full screen MPEG-2 decoding & playback. A PIII-500
might
> be
> OK there.

Based on your above comments, and based on what I have now, if I buy a
Hauppauge PVR-250 or 350 and use the current ATI TV wonder as my second
tuner, am I correct in assuming that having only one PVR-250/350 will
force me to still have at least a 1 GHZ processor for recording and
watching live tv at the same time?

Thanks for your input!

John

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http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users

RE: A noob question regarding hardware req. andhardwarecodecs [ In reply to ]

jcaputo1 at comcast

Aug 5, 2003, 10:50 AM

Post #4 of 10 (2165 views)

Permalink

> -----Original Message-----
> From: mythtv-users-bounces@mythtv.org
> [mailto:mythtv-users-bounces@mythtv.org]On Behalf Of John Wells
> Sent: Tuesday, August 05, 2003 1:32 PM
> To: Discussion about mythtv
> Cc: Discussion about mythtv
> Subject: RE: [mythtv-users] A noob question regarding hardware req.
> andhardwarecodecs
>
>
> Joseph:
>
> Joseph A. Caputo said:
> > Probably not with your current hardware. Possibly with a
> hardware encoder
> > (see below).
> > General rule of thumb: ~1GHz per encoding stream, + at ~500MHz for
> > playback.
> > I've got an Athlon XP 1600+ handling a single V4L tuner, which is just
> > about
> > enough power. It'd be nice to have a little more breathing
> room, though.
> > I
> > definitely couldn't handle 2 V4L tuners without *really* sacrificing
> > quality.
> >
> >> 2. If I buy a hardware encoder like the Haupauge 250 or 350, what sort
> >> of
> >> effect will that have on CPU requirements? Assuming a purchase of one
> >> of
> >> those cards, what CPU could I get buy with?
> >
> > A hardware MPEG encoder reduces the encoding load on your processor to
> > virtually nothing. Thus, with such a setup you really only
> need a system
> > that can handle full screen MPEG-2 decoding & playback. A
> PIII-500 might
> > be
> > OK there.
>
> Based on your above comments, and based on what I have now, if I buy a
> Hauppauge PVR-250 or 350 and use the current ATI TV wonder as my second
> tuner, am I correct in assuming that having only one PVR-250/350 will
> force me to still have at least a 1 GHZ processor for recording and
> watching live tv at the same time?

If you want to be able to simultaneously record with both tuners while
watching one playback stream (as you've indicated), then yes. Some people
have reported being able to do LiveTV (single record/playback) with as
little as 700MHz (without a hardware encoder), if they crank down the
capture resolution to 320x240 and use RTjpeg. For the combination of
hardware & desired capabilities that you've described, you probably want
somewhere in the 1-1.5 GHz range to be comfortable. Also, keep in mind that
because they use MPEG-2, the hardware MPEG cards produce very large files
(~6 GB/hr), so that 40GB HD might fill up awfully fast...

-JAC

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RE: A noob question regarding hardware req. andhardwarecodecs [ In reply to ]

ray at comarre

Aug 5, 2003, 11:01 AM

Post #5 of 10 (2166 views)

Permalink

At 01:31 PM 8/5/2003 -0400, John Wells wrote:
[...]
>Based on your above comments, and based on what I have now, if I buy a
>Hauppauge PVR-250 or 350 and use the current ATI TV wonder as my second
>tuner, am I correct in assuming that having only one PVR-250/350 will
>force me to still have at least a 1 GHZ processor for recording and
>watching live tv at the same time?

At least 1 GHz; maybe more. As Joseph said, his rule of thmb is 1 GHz for
encoding, 500 MHZ for decoding. (My experience is about the same as his
here, BTW.) Since watching "live" TV with Myth involves a buffer, you are
both encoding and decoding. So the arithmetic says you need 1.5 GHz for
"live" TV with software encoding. Plus a bit for simultaneous operation of
the PVR-250 ... its CPU load should be light, but that's not the same as zero.

Joseph's rule of thumb is a bit cautious; you can get by with less than it
specifies, by making some quality tradeoffs. Reduce capture resolution to
320x240 (for NTSC; PAL is just a tad higher) and you'll probably get by
with 1 GHz ... though only you can decide if this quality meets your
standards.

RE: A noob question regarding hardware req.andhardwarecodecs [ In reply to ]

jb at sourceillustrated

Aug 5, 2003, 11:29 AM

Post #6 of 10 (2165 views)

Permalink

Joseph A. Caputo said:
> If you want to be able to simultaneously record with both tuners while
> watching one playback stream (as you've indicated), then yes. Some people
> have reported being able to do LiveTV (single record/playback) with as
> little as 700MHz (without a hardware encoder), if they crank down the
> capture resolution to 320x240 and use RTjpeg. For the combination of
> hardware & desired capabilities that you've described, you probably want
> somewhere in the 1-1.5 GHz range to be comfortable. Also, keep in mind
> that
> because they use MPEG-2, the hardware MPEG cards produce very large files
> (~6 GB/hr), so that 40GB HD might fill up awfully fast...
>

Well, I really only want to be able to record with one tuner and use the
other as a playback stream (i.e., I don't really need to record two shows
at once).

Ah, but I guess live pause capability would require a second recording, so
if that's what you mean, then yes....

Thanks!

John

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RE: A noob question regarding hardware req.andhardwarecodecs [ In reply to ]

wd at pobox

Aug 5, 2003, 11:47 AM

Post #7 of 10 (2169 views)

Permalink

>somewhere in the 1-1.5 GHz range to be comfortable. Also, keep in mind that
>because they use MPEG-2, the hardware MPEG cards produce very large files
>(~6 GB/hr), so that 40GB HD might fill up awfully fast...
>
>-JAC

The PVR250 has a configurable bitrate. I have mine set for 2.5-3GB/hour,
which is still probably overkill. If you have a small HD, then you can
bump it down as low as you like.

-WD

Re: A noob question regarding hardware req. andhardwarecodecs [ In reply to ]

peraage at leneogperaage

Aug 5, 2003, 12:04 PM

Post #8 of 10 (2165 views)

Permalink

Ray Olszewski wrote:
> At 01:31 PM 8/5/2003 -0400, John Wells wrote:
> [...]
>
>> Based on your above comments, and based on what I have now, if I buy a
>> Hauppauge PVR-250 or 350 and use the current ATI TV wonder as my second
>> tuner, am I correct in assuming that having only one PVR-250/350 will
>> force me to still have at least a 1 GHZ processor for recording and
>> watching live tv at the same time?
>
>
>
> At least 1 GHz; maybe more. As Joseph said, his rule of thmb is 1 GHz
> for encoding, 500 MHZ for decoding. (My experience is about the same as
> his here, BTW.) Since watching "live" TV with Myth involves a buffer,
> you are both encoding and decoding. So the arithmetic says you need 1.5
> GHz for "live" TV with software encoding. Plus a bit for simultaneous
> operation of the PVR-250 ... its CPU load should be light, but that's
> not the same as zero.
>
> Joseph's rule of thumb is a bit cautious; you can get by with less than
> it specifies, by making some quality tradeoffs. Reduce capture
> resolution to 320x240 (for NTSC; PAL is just a tad higher) and you'll
> probably get by with 1 GHz ... though only you can decide if this
> quality meets your standards.
>
>
>

Just another experience here:

512x480, 3200kbps mpg4 watching live tv lets my 1600xp run with 35-40%
idle. I can't believe the poor performance you are getting out of your
systems. Maybe it's the vidcard XV support that's partially done in
software ?

--

perage

Re: A noob question regarding hardware req. [ In reply to ]

cpinkham at bc2va

Aug 5, 2003, 1:29 PM

Post #9 of 10 (2168 views)

Permalink

> Just another experience here:
>
> 512x480, 3200kbps mpg4 watching live tv lets my 1600xp run with 35-40%
> idle. I can't believe the poor performance you are getting out of your
> systems. Maybe it's the vidcard XV support that's partially done in
> software ?

I second that. I was able to run 352x480 LiveTV on my Athlon 700 using
mpeg4 compression with 3300Kbit/sec scaled (which comes to around
1800-2000Kbit/sec when myth scales the bitrate down since I was running
at 352x480 instead of 640x480). Trying to go up to 384x480 would cause
skips occasionally, but 352x480 worked ok for either LiveTV or for
watching a prerecorded show while another was recording.

Lots of things come into play as to why some people can't get good
performance, mainly video and sound related issues I think (ie, how
much cpu is being used just to capture and display the raw data not counting
encoding/decoding).

--

Chris

Re: A noob question regarding hardware req. and hardwarecodecs [ In reply to ]

bstoneaz at cox

Aug 6, 2003, 12:38 AM

Post #10 of 10 (2156 views)

Permalink

freevo will not let you pause live tv

----- Original Message -----
From: "John Wells" <jb@sourceillustrated.com>
To: <mythtv-users@mythtv.org>
Sent: Tuesday, August 05, 2003 9:32 AM
Subject: [mythtv-users] A noob question regarding hardware req. and
hardwarecodecs

> Hi guys. New to the list and MythTV and have a few questions, if you
> don't mind.
>
> Here's what I'd like to do with my Freevo or MythTV PVR:
>
> R.1 - Watch live tv while recording another show on another channel
> R.2 - Watch live tv while recording the currently viewed show.
> R.3 - Pause live tv.
>

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