[mythtv-users] Varying data formats during digital reception

Mark Greenwood fatgerman at gmail.com
Tue Nov 6 14:29:17 UTC 2012


On Tuesday 06 Nov 2012 14:14:00 Jose Paulo Moitinho de Almeida wrote:
> On Tuesday 06 November 2012, John Pilkington wrote:
> > On 06/11/12 10:38, Jose Paulo Moitinho de Almeida wrote:
> > > On Tuesday 06 November 2012, John Pilkington wrote:
> > >> On 05/11/12 23:26, JP Moitinho de Almeida wrote:
> > >>> On Monday 05 November 2012 18:40:21 John Pilkington wrote:
> > >>>> On 05/11/12 17:46, Jose Paulo Moitinho de Almeida wrote:
> > >>>>>> ...problem is, he has to get the program started before he can use
> > >>>>>> the editor to set the cutpoints...
> > >>>>>> 
> > >>>>>> possible if you have sufficient padding before the actual content
> > >>>>>> starts, I suppose. But will the editor fail be
> > >>>>>> cause the format changed, even so?
> > >>>>> 
> > >>>>> I am not at home but, effectively, using the editor is not possible.
> > >>>>> Editing those files past that point also hangs the frontend.
> > >>>>> 
> > >>>>> But I can work with "tail/head -c" by iteration/bisection of the
> > >>>>> file, until I just capture the zone of the relevant point.
> > >>>>> 
> > >>>>> I'll post that tonight.
> > >>>>> 
> > >>>>> Regards
> > >>>>> 
> > >>>>> ZP
> > >>>> 
> > >>>> Or:  mv infile.mpg infile.mpg0
> > >>>> 
> > >>>> dd bs=1M skip=35  count=40 if=infile.mpg0 of=infile.mpg
> > >>>> 
> > >>>> adjust the skip number and see if it plays in Myth, then omit the
> > >>>> count.
> > >>> 
> > >>> The link has a 10 Mb clip where the format changes. With this short
> > >>> version the frontend gives up without hanging, but the problem is
> > >>> clearly there.
> > >>> 
> > >>> http://dl.dropbox.com/u/20086953/myth_samples/12002_20121104214000.mpg
> > >>> 
> > >>> (thanks for the dd, I was missing the skip option)
> > >>> 
> > >>> Regards
> > >>> 
> > >>> ZP
> > >> 
> > >> For me vlc plays for 35 sec, mythtv as a recording (overwriting a short
> > >> recording made here) or as a video for about 30 sec until the presenter
> > >> walks on, then returns to the Watch Recordings screen.  If that's where
> > >> you see the problem it might be better to have more data after it.
> > >> 
> > >> There's a change in aspect ratio just after the yellow countdown, but
> > >> that doesn't seem to be a problem.  I didn't notice it initially.
> > >> 
> > >> You might find the vlc  'Tools > Codec info' informative.
> > >> 
> > >> All in MythTV 0.25.3.
> > >> 
> > >> John
> > > 
> > > The problem happens with the aspect ratio change, which played without
> > > problems in 0.25.
> > > 
> > > After updating to 0.26 the video stops there and then the frontend player
> > > stops. With a longer sample the frontend player takes (much) longer to
> > > give up.
> > > 
> > > The log is full of "AFD: Unknown decoding error" messages (text written
> > > from memory).
> > > 
> > > Regards
> > > 
> > > ZP
> > 
> > I've run ffmpeg -i from the start and from the middle of this file,
> > which has been renamed to look like a local recording:
> > ------------------
> > ffmpeg -i 1001_20121106090300.mpg 2>&1 | grep -C 4 stereo
> >    Duration: 00:00:35.96, start: 67743.186556, bitrate: 2332 kb/s
> >    Program 1
> >      Stream #0:0[0x21](por): Subtitle: dvb_teletext ([6][0][0][0] / 0x0006)
> >      Stream #0:1[0x200]: Video: h264 (Main) ([27][0][0][0] / 0x001B),
> > yuv420p, 720x576 [SAR 16:11 DAR 20:11], 53.85 fps, 50 tbr, 90k tbn, 50 tbc
> >      Stream #0:2[0x201](por): Audio: aac_latm ([17][0][0][0] / 0x0011),
> > 48000 Hz, stereo, s16
> > 
> > -----------------------
> > dd bs=1M skip=5   if=1001_20121106090300.mpg of=tmp.mpg
> > 
> > ffmpeg -i tmp.mpg  2>&1 | grep -C 4 stereo
> >    Duration: 00:00:12.92, start: 67766.226556, bitrate: 3246 kb/s
> >    Program 1
> >      Stream #0:0[0x21](por): Subtitle: dvb_teletext ([6][0][0][0] / 0x0006)
> >      Stream #0:1[0x200]: Video: h264 (Main) ([27][0][0][0] / 0x001B),
> > yuv420p, 720x576 [SAR 12:11 DAR 15:11], 61.14 fps, 50 tbr, 90k tbn, 50 tbc
> >      Stream #0:2[0x201](por): Audio: aac_latm ([17][0][0][0] / 0x0011),
> > 48000 Hz, stereo, s16
> > ---------------
> > 
> > This email format make it difficult to see, but the main changes appear
> > to be the aspect ratio and fps, which looks strange.
> > 
> > Without the grep, ffmpeg complains a lot and reports an audio format
> > change.
> > 
> > [aac_latm @ 0x12aca00] audio config changed
> > 
> > [h264 @ 0x12ac040] non-existing PPS referenced
> > [h264 @ 0x12ac040] non-existing PPS 0 referenced
> > [h264 @ 0x12ac040] decode_slice_header error
> > [h264 @ 0x12ac040] no frame!
> > 
> > I tried it via UPnP on my Panasonic tv, too.  As a recording it played
> > straight through to the end with no apparent aspect ratio change.  As a
> > Video I get 'Cannot read file'.  It would be nice to understand this!
> > 
> > John P
> > 
> 
> It would be great if someone with 0.26 and another decoder (vdpau, probably) 
> could check whether the file plays properly. 

I have 0.26 (on mythbuntu 12.04) and VDPAU. I tried a few things.

Plays fine in mythtv (as a Movie, not sure if that matters)
Plays fine in mplayer when mplayer is set to use vdpau output
Set mplayer to use xv output and the video stops at the change of aspect but the audio carries on. The mplayer output gives you the problem:

[h264 @ 0x7faa4c59e280]Width/height changing with threads is not implemented. Update your Libav version to the newest one from Git. If the problem still occurs, it means that your file has a feature which has not been implemented.
[h264 @ 0x7faa4c59e280]decode_slice_header error
[h264 @ 0x7faa4c59e280]no frame!

HTH

Mark


> Unless someone has a magic solutions, the following step is  to check the 
> ffmpeg decoder to see how it handles (or not) a change of aspect ratio/fps in 
> the middle of a stream.
> 
> So I think that the question initially raised by Mike Perkins
> 
> > The question is: What changes are being made to mythtv to cope with the fact 
> > that the bitrate, framerate, resolution, etc of any recorded file may change 
> > from instant to instant?
> 
> May (at least for my problem) be changed to:
> 
> What changed from 0.25 to 0.26, causing the decoder to have problems when the  
> aspect ratio/fps changes from instant to instant?
> 
> My guess (only a guess) is that it is the aspect ratio change that chokes it.
> 
> Any pointers?
> 
> ZP
> 
> 
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