[mythtv-users] problem: AC3 audio on 1080i playback

Matt W mwood23 at gmail.com
Wed Feb 10 11:27:55 UTC 2010


Hi all--

been slowly getting my system up to speed for HD playback.  I have
most of the problems worked out.  In particular, I can get great
playback on 720p material, even with AC3 SPDIF to my a/v receiver.
The receiver detects 'Dolby Digital' and hums along.

I just don't seem to have the same luck with 1080i content.  The
picture runs fine, but the audio is stuttered with many dropouts.  in
fact it's mostly silence with occasional blips of sound.  If I change
the audio track to the 2 channel (e.g. NOVA on PBS has three
tracks(!)) then things perform fine.

Am I just SOL when it comes to trying to do this?  I know my system
isn't super modern but I thought it would be able to hack it:

AMD Athlon X2 5050e (2.6Ghz with 2x512k L2)
2GB RAM, 800 DDR2, 128 bit interleaved
Asus M2NPV-VM
onboard video: Nvidia 6150
BIOS 'frame buffer' value set to 256MB
onboard sound: Analog Devices AD1986A
nvidia glx drivers 173.14.09-5
alsa drivers 1.0.16-2
MythTV trunk Revision: 23341
Debian 5.0, AMD64

I've ticked 'aggressive audio buffering' and playing from various
playback profiles.  In fact, things seem to go better without XvMC
although I guess that isn't a complete surprise.  A weird thing is, I
don't see any of the usual suspects like 'prebuffering pause'  or
'writeaudio: buffer underrun' at the times of the stuttering 1080/5.1
playback.

Before I waste time chasing diminishing returns, is there anything
obvious I'm missing?    I was thinking of trying the latest Nvidia
drivers (190.x?) and/or compiling the latest ALSA drivers in the hopes
of scraping a bit of performance out of them from compiler
optimizations.

Anyone been down this road?  any input appreciated.  thanks!


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