[mythtv] Re: mythtv-dev digest, Vol 1 #287 - 28 msgs

[Bruce Markey]

Dr. J. S. Pezaris wrote:
>     From: Bruce Markey <bjm@lvcm.com>
>     To: mythtv-dev@snowman.net
>     Subject: Re: [mythtv] WinTV PVR-250 (hardware mpeg encoder)
>     
>     I'm told that there are up to 933MHz CPUs that don't need
>     fans. This should be fast enough to encode mpeg4 and
>     playback at 640x480 but is certainly fast enough for the
>     MythTV default of 480x480.
>     
> I've tried running MythTV on one of the EPIA 800 MHz C3 CPUs.  These chips
> have the effective equivalent of a 500 MHz P-III in terms of integer
> computational power, but have quite awful floating-point performance.  They
> certainly are NOT fast enough for the MythTV default of 480x480 with no
> dropped frames.  At least that's my experience; maybe things have changed
> since the last time I tried.

Of course, that would be expected with the equivalent of 500MHz
performance. I was referring to a processor at nearly twice the
speed. However, is this the real underlying issue? You don't
want to upgrade this machine? If you must have a fanless CPU,
you could get a 933MHz processor which should be adequate.

>     I personally don't believe the CPU fan is a make or break
>     issue. I have a system with a 1.2GHz AMD (currently $31)
>     and a WinTV model 401 ($29) that can record up to 720x480
>     mpeg4 or two tuners at 352x480 with no jitter. I'd rather
>     have this today than pay $140 for a card that has no open
>     source Linux drivers.
> 
> I am not advocating supporting the WinTV board in particular, but any board
> with harware encode/decode.

I've been waiting for Linux support for any board with hardware
encode/decode for over two years and it doesn't exist yet. I
doubt there will be any Linux drivers this year either. You
should direct your advocacy to manufactures to release their
technical specs. or to device driver maintainers to reverse
engineer these cards. You can find dozens of MPEG capture cards
listed at http://www.vcdhelp.com/capturecards . I periodically
do searches to find any projects that successfully support any
MPEG card for Linux. There aren't any.

The source of the discussion on this list is that there recently
were two different experiments. By stealing the windoze binaries
and putting Linux wrappers around them you can get some limited
results. This is NOT an open source driver with an API ready for
applications to use.

If anyone was under the impression that there was blanket
opposition to encoding cards, I don't believe this is the
case. There should, however, be opposition to "hanging a bag
off the side" of MythTV to support a kluge driver in violation
of the license. (I expect several non lawyers to respond to
this point with their interpretation of the license ;-).

> Please give the details of your fanless system.

Oh, come on. You read my message and you must know that I
have a CPU fan on every machine in my house and I'm happy
that I have them. If, someday, I have a system with a
supported MPEG card, there will be a CPU fan in that
machine too.

I've had an HP mini-tower (that I've upgraded a few times)
in my home entertainment center for years. I don't always
have it turned on and I need to look at the light to tell
if it is on. I hear the AC, I hear the refrigerator come
on, the wind blow, etc. I don't hear the PC and certainly
cannot identify the sound that the CPU fan makes.

All the arguments against CPU fans will not make drivers
for MPEG cards suddenly appear.

> ...I was not able to get
> MythTV to work beyond low-resolution proof-of-concept level on an Via EPIA
> 800 MHz C3 system.  Given the descriptions of systems and loads that Isaac
> and other people have posted, it still seems that using a cpu which
> requires a fan (THAT is the key, not the fan itself, but that one needs a
> power-hungry and high-heat-dissipation CPU ... this leads to requiring a
> fan, a larger power supply which now requirs a fan, etc.) is a prerequisite
> for a reasonable MythTV system.

This presumes that if 500MHz is inadequate, the trappings
of a 2-3Ghz CPU are required. This is not true. I would
specifically recommend an AMD Duron 1.2 or 1.3GHz CPU. These
are the slowest, cheapest chips that I can currently find
in retail stores. They can easily do 640x480 mpeg4 for a
single tuner system. They are designed to run much cooler
than the Athlon series. I have a Duron 1.2 with a cheap fan
that runs so close to room temperature that I overclock it out
of embarrassment ;-). A 250 watt power supply should do and
no other case fan needed.

--  bjm

PS I've seen discussions (on this list and several other) over
the merits of hardware encoding. If I were arguing for encoding
cards, I'd avoid the CPU fan issue altogether because that's
just blowing hot air (sorry, I couldn't resist ;-). The more
persuasive technical arguments are that the on-board chip is
not subject to context switching and the compressed video does
not need as much of bandwidth on the bus. However, with current
CPU and bus speeds, software compression is cheaper and more
flexible and therefore the better solution anyway. I'm not
opposed to MPEG cards and hope they will have Linux support
someday soon.