[mythtv-users] Varying data formats during digital reception

Jose Paulo Moitinho de Almeida moitinho at civil.ist.utl.pt
Tue Nov 6 14:14:00 UTC 2012


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. 

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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