[mythtv-users] Preserving HDTV AC3 audio stream whilst transcoding

[Joe Barnhart]

--- Isaac Richards <ijr at po.cwru.edu> wrote:

> Current CVS myth, a gf4 (4200), 66.26 drivers, not
> using XvMC (slower than Xv 
> without a better card), no deinterlacing/filtering,
> doesn't matter what 
> display res.  'Extra audio buffering' is turned on.
> 
> 720p plays perfectly on this machine.
> 
> Of course, none of that is with the OSD displaying
> anything during playback - 
> I don't have enough cpu to blend in software. =)

I'm puzzled by the statement that the cpu usage
"doesn't matter what display res."

A simple calculation shows that a stream played at
1080i with 24-bit color pushes about 1.5Gbps through
the video card (1920x1080 x30fps x24bpp).  A 720p
stream pushes about 1.3Gbps.  If your output device is
720x480i, you're looking at about 250Mbps.  I would
think the difference in these OUTPUT resolutions would
have a profound effect on system performance.

I have had severe difficulty playing 720p or 1080i
source on my 1080i output device with an Athlon 2800. 
The player built into Myth just couldn't keep up with
it, regardless of extra audio buffering or any other
setting.  This was while using Xv.  If I changed to
XvMC I could play the stream, but it would hang if I
tried to jump forward or backward, or whenever the OSD
tried to fade off screen.  It was just not usable with
XvMC.

Because I obviously needed more horsepower to use Xv
at 1080i output, I bought a P4 3200 machine and I'm
now able to play HD sreams smoothly.  All of my
experiments are with plain 0.16 MythTv under
KnoppMyth.

I don't have any comparisons with Xine or Mplayer, but
I can say for sure that the player built into Myth is
not able to keep up with 1080i while playing on an
Athlon 2800 or slower, using Xv and a nVidia 5200 (8x
AGP).

I'm interested in trying some of the later work done
by Doug and others.  I'll be able to try CVS at some
point, and then I can begin to try the patches.


		
__________________________________ 
Do you Yahoo!? 
Meet the all-new My Yahoo! - Try it today! 
http://my.yahoo.com