[mythtv-users] mythtv audio stuttering on 720p material after upgrade to Fedora 9
dl-mythtv at catspoiler.org
Sat Sep 20 01:39:41 UTC 2008
On 15 Sep, Don Lewis wrote:
> Yesterday I upgraded my myth box from 0.21 and Fedora 7 to the latest
> 0.21+fixes and Fedora 9 using the rpms from atrpms.net. My hardware is
> an Athlon 64 X2 4000+ on an Abit AN-M2HD motherboard with 1GB of RAM.
> I'm using the onboard GeForce 7050 graphics and driving my TV in 720P
> mode through HDMI output. Sound output is via the motherboard S/PDIF
> output. The video driver is the latest from Nvidia. I'm using ffmpeg +
> XVideo. I've got UseEvents set to "true" in xorg.conf.
> Before the upgrade, the only playback problem that I had was occasional
> tearing that was mostly visible during horizontal pans, probably because
> I haven't been able to enable OpenGL vertical sync.
> Almost everything works fine since the upgrade. The exception is
> playback of previously recorded 720P material. SD material works fine,
> as does 1080i material, as long as I don't use an overly expensive
> deinterlace mode.
> When I try to play a recording that was broadcast in 720P, the audio
> stutters every few seconds and the video seems to alternate between
> running at full speed and at about half speed with the same rhythm as
> the audio problems. When the audio drops out, my receiver shows that
> the digital audio signal has has been lost. The problem is much worse
> if I disable the extra audio buffering. Then I only get brief snippets
> of sound, and the video appears to be running slow all the time. I've
> tried twiddling a bunch of the playback knobs and nothing seems to help.
> CPU usage is low, maybe 30%,, and the problem still occurs even if I set
> deinterlacing to none. I can play the same recording using mplayer and
> it works just fine. The log file shuws a bunch of buffer underruns:
I'm still tearing out my hair over this problem. When playing 720p
material, mythfrontend uses anywhere from 35% to 50% of one CPU core,
and Xorg uses about 10%. The idle CPU percentage is anywhere from 72%
to 80%. Idle CPU drops to a consistent 68% to 70% when viewing 1080i
material, which plays cleanly.
I wouldn't expect enabling realtime threads to help, and it doesn't. I
did notice that when viewing all the threads in top that only one of the
mythfrontend threads (video display?) was running at an elevated
priority, so if sound is being written by another thread, it is only
running at the normal priority. With this much idle CPU, I wouldn't
think that should make a difference.
Nothing of the changes I've tried making to the playback profile have
helped, in particular changing the decoder, the number of CPUs for
decoding, or changing the deinterlace mode (which shouldn't be needed
for 720p anyway, right?).
I've got the sound configured to do AC3 passthrough to the S/PDIF
output, but I still get massive stuttering with analog audio out. The
only sound configuration change that makes a difference is enabling
extra buffering, which gets me from sound 10% of the time to 40% of the
time. If I set the audio output to "None", then the video output looks
smoother, probably because the prebuffering pauses are going away.
The sound is messed up with both Dolby Digital and Dolby Pro Logic II
The drive where the video file resides doesn't matter.
Doing a database optimization doesn't help.
1080i material plays fine through mythfrontend, and the 720p material
that mythfrontend doesn't like plays fine through mplayer.
About the only thing I haven't tried yet is adding more RAM. I'm not
seeing signs of paging, but I ordered another 2GB of RAM anyway.
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