[mythtv-users] Recent DVD problems with video and audio drops

[James Courtier-Dutton]

On Jan 20, 2013 11:30 PM, "Neil Salstrom" <salstrom at gmail.com> wrote:
>
> On Sat, Jan 19, 2013 at 4:48 AM, Richard <peper03 at yahoo.com> wrote:
>
> > A DVD can either be 29.97 or 25 fps depending on whether it's NTSC or
PAL.
> > If it's an NTSC disc and should be played at 24fps (or 23.96 or
whatever the
> > actual value is) it performs a pull-down.  To be honest, I have very
little
> > experience with this and nearly all my DVDs are PAL.
> > I just tried one of the region 1 DVDs I have and that reported ~23.97fps
> > too.  Also there are chunks of your logs where there is apparently no
> > playback problem and it's still reporting around the same frame rate.
> >
> > The frame rate shown is more the actual framerate rather than the
intended
> > framerate, which is why it sometimes jumps around a bit when you get
> > playback issues.
>
> Ahh...  I think I'm beginning to understand.  Sorry for the beginner
> questions from me.  The original film was 24fps (well, 23.96).  The
> movie on the disk is 29.97fsp but pulldown occurs to bring it back to
> the native 23.96?  Is this being done via a VDPAU deinterlace
> function?
>
> >
> > Could you try again with -v playback,timestamp --loglevel=debug? That'll
> > spew out an awful lot of messages but may help identify timing issues.
 It's
> > probably not necessary to post the entire log (it's possible you hit
> > pastebin's limits) but a section starting before the playback issues
occur
> > would be good.
>
> I had a brief moment of inspiration and decided to start mythtv via a
> terminal window on my laptop.  I did "export DISPLAY=:0" then I was
> able to start mythtv on my HTPC and watch the resulting log messages
> as they occurred.  I've been watching after starting the frontend with
> -v playback,timestamp --loglevel=debug but that puts out a HUGE amount
> of data.  I've managed to pause right after a series of judders but I
> can't make much of the logs.
>
> There is audio dropout as well during these stutters.  My receiver
> gives a little click when an audio source is cut off or changed and I
> get a rapid series of clicks when this happens.
>
> One thing I do see occasionally is:
>
> 2013-01-20 15:12:41.739847 I  VidOutVDPAU: Frame E is in use by avlib
> and so is being held for later discarding.
> 2013-01-20 15:12:41.776279 I  VidOutVDPAU: Frame E is in use by avlib
> and so is being held for later discarding.
> 2013-01-20 15:12:41.812685 I  VidOutVDPAU: Frame E is in use by avlib
> and so is being held for later discarding.
>
> Here is a pastebin of a log that encompasses several seconds where the
> dropouts occurred:
>
> http://pastebin.com/hZPq8fhe
>
> I also ran it without timestamp but with playback,audio.  I see a lot of
this:
>
> 2013-01-20 15:23:31.949383 I  Player(0): Waiting for video buffers...
> 2013-01-20 15:23:32.010041 I  Player(0): Waiting for video buffers...
> 2013-01-20 15:23:32.018994 I  ALSA: WriteAudio: buffer underrun
> 2013-01-20 15:23:32.102758 I  Player(0): Waiting for video buffers...
> 2013-01-20 15:23:32.221823 I  Player(0): Waiting for video buffers...
> 2013-01-20 15:23:32.257906 I  ALSA: WriteAudio: buffer underrun
> 2013-01-20 15:23:32.341658 D  DVDRB: DVDNAV_NAV_PACKET
> 2013-01-20 15:23:32.736604 D  DVDRB: DVDNAV_NAV_PACKET
> 2013-01-20 15:23:33.142852 I  Player(0): FPS:   20.89 Mean: 47872
> Std.Dev: 18452 CPUs: 100% 100% 312%
> 2013-01-20 15:23:33.376318 D  DVDRB: DVDNAV_NAV_PACKET
> 2013-01-20 15:23:33.976712 I  Player(0): Waiting for video buffers...
> 2013-01-20 15:23:34.016253 D  DVDRB: DVDNAV_NAV_PACKET
> 2013-01-20 15:23:34.061232 I  ALSA: WriteAudio: buffer underrun
> 2013-01-20 15:23:34.065159 I  Player(0): Waiting for video buffers...
> 2013-01-20 15:23:34.134498 I  Player(0): Waiting for video buffers...
> 2013-01-20 15:23:34.260119 I  ALSA: WriteAudio: buffer underrun
> 2013-01-20 15:23:34.346417 I  Player(0): Waiting for video buffers...
> 2013-01-20 15:23:34.419615 I  ALSA: WriteAudio: buffer underrun
> 2013-01-20 15:23:34.429152 I  Player(0): Waiting for video buffers...
> 2013-01-20 15:23:34.494282 I  Player(0): Waiting for video buffers...
> 2013-01-20 15:23:34.632919 I  Player(0): Waiting for video buffers...
> 2013-01-20 15:23:34.693593 I  Player(0): Waiting for video buffers...
> 2013-01-20 15:23:34.737113 D  DVDRB: DVDNAV_NAV_PACKET
> 2013-01-20 15:23:34.739825 I  ALSA: WriteAudio: buffer underrun
>
> Are the alsa buffer underruns involved?  If this is the case, why does
> it only happen with the DVD and not a mkv which has the exact same
> audio and video?
>
> Thanks!

This is most likely a 3:2 pull down problem. Problem will only happen on
NTSC movie dvds and not PAL.
The problem is caused when the software recognises that a 30 fps dvd can be
played back at 24 fps due to the repeat first field flag in the stream.
When doing this, the software should also change all the frame timestamps.
My guess is that myth is not redoing the timestamps as it should.

James
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