[mythtv-users] Stuttering in DVD menus

Richard peper03 at yahoo.com
Sat Nov 10 13:52:19 UTC 2012

On 19/09/12 21:36, Richard wrote:
> Hi,
> Most of the DVDs I've tried recently suffer from stuttering audio/video
> in the menus.  It only seems to affect animated menus and only when
> VDPAU is used for playback.  OpenGL works fine but that gives me other
> issues watching recordings so I'd rather not use OpenGL.
> I've tried ripping a DVD to ISO and playing it back from the local hard
> drive to make sure it wasn't some sort of issue with the DVD itself but
> it doesn't help.
> Starting mythfrontend with -v audio,playback gives lots of errors:
> 2012-09-19 21:29:38.611274 I  AO: enc(0), passthru(0), features (LPCM)
> configured_channels(2), 2 channels supported(1) max_channels(2)
> 2012-09-19 21:29:38.611282 I  AO: Audio processing enabled
> 2012-09-19 21:29:38.611294 I  AO: Opening audio device
> 'plughw:CARD=PCH,DEV=0' ch 2(2) sr 48000 sf signed 32 bit reenc 0
> 2012-09-19 21:29:38.611300 I  ALSA: OpenDevice plughw:CARD=PCH,DEV=0
> 2012-09-19 21:29:38.611507 I  ALSA: SetParameters(format=10, channels=2,
> rate=48000, buffer_time=500000, period_time=4)
> 2012-09-19 21:29:38.611753 I  ALSA: Buffer size range from 32 to 8192
> 2012-09-19 21:29:38.611760 I  ALSA: Period size range from 16 to 4096
> 2012-09-19 21:29:38.611796 I  ALSA: Buffer time = 170666 us
> 2012-09-19 21:29:38.611850 I  ALSA: Period time = 4 periods
> 2012-09-19 21:29:38.611996 I  ALSA: Buffer size = 8192 | Period size = 2048
> 2012-09-19 21:29:38.612032 I  AO: Audio fragment size: 8192
> 2012-09-19 21:29:38.612037 I  AO: Software volume enabled
> 2012-09-19 21:29:38.645069 I  AO: Audio Stretch Factor: 1
> 2012-09-19 21:29:38.645109 I  AO: Ending Reconfigure()
> 2012-09-19 21:29:38.645196 I  AO: kickoffOutputAudioLoop: pid = 5820
> 2012-09-19 21:29:38.645215 I  AO: OutputAudioLoop: Play Event
> 2012-09-19 21:29:38.784646 I  AFD: Key frame distance changed from 15 to
> 11.
> 2012-09-19 21:29:38.875333 I  Player(0): Video is 4.82812 frames ahead
> of audio,
>                          doubling video frame interval to slow down.
> 2012-09-19 21:29:38.995329 I  Player(0): Video is 6.19607 frames ahead
> of audio,
>                          doubling video frame interval to slow down.
> 2012-09-19 21:29:39.057410 I  ALSA: WriteAudio: buffer underrun
> 2012-09-19 21:29:39.115321 I  Player(0): Video is 6.72205 frames ahead
> of audio,
>                          doubling video frame interval to slow down.
> 2012-09-19 21:29:39.235328 I  Player(0): Video is 6.62278 frames ahead
> of audio,
>                          doubling video frame interval to slow down.
> I don't get stuttering playing back recordings (whether HD or SD) nor in
> the actual film itself - only in animated DVD menus.
> Does anyone have any ideas what the root cause of the problem could be?

After waiting to upgrade to 0.26 to see if anything had changed there, I 
can now report on what progress I've made:

1. The problem still exists in 0.26
2. It seems to be caused by selecting 'VDPAU' as the decoder.  The 
chosen renderer is irrelevant.  It doesn't occur when I select the 
'Standard' (ffmpeg) decoder.

Decoding using ffmpeg isn't the perfect solution though, because I've 
found playback isn't always smooth if I allow it to use more than one 
core.  It's particularly noticeable when the camera pans.  It's not 
really jerky, but it's noticeably less smooth than when decoding using 
VDPAU.  Also, skipping forwards and backwards using ffmpeg doesn't look 
nice.  You seem to get the first new frame, followed by the last old 
frame, before playback continues with new frame+1.  It works, but it 
feels jerky.

All in all, VDPAU decoding seems to work better than ffmpeg decoding in 
all areas except DVD menus.

I still don't understand why this should only affect playback of DVD 
menus.  What's different about a menu?  The traces seem to indicate that 
video decoding is ahead of audio but is there a some way to determine 
whether it's a video or an audio problem?

Is the DVD player Myth code, or is it imported from an external project?

I'm also surprised that almost no-one else seems to have this problem. 
Are Neil and I the only people trying to watch DVDs with an NVidia card? 
  I realise that it's a combination of a couple of things but nothing 
that's out of the ordinary (or maybe it is?).


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