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

[Richard]

On 21/01/13 00:30, Neil Salstrom 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?

Yes (although I haven't looked in detail at where it's done).

> 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.

Join the club! :(

> 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.

This comes when a frame hasn't been released.  I'm afraid I'm not sure 
of the exact details.

> 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?

I think the underruns are a consequence of the 'Waiting for video 
buffers' message.  The player sleeps for a bit and I think in that time, 
the audio section runs out of data to play.

To be honest, I'm rapidly reaching the limits of my knowledge (in case 
that isn't apparent!).  Studying the code hasn't given me any flashes of 
inspiration either, unfortunately :(

I got a copy of Inception from my friend, but as I expected, I've not 
seen the same issues.

I don't know how much the answers will help but I've still got a couple 
of questions:

1. Does the DVD play ok with other software players (e.g. VLC)?
2. Do the playback issues always occur at the same place, or not at the 
same place but after X seconds of playback?  Or is the position random?
3. Has this issue only surfaced recently?  Did the affected DVDs play 
without problems previously?  If only recently, any idea how recently? 
Is it possible you've changed any hardware or audio/playback settings?

Richard.