[theora] video quality problem, encodeing with ffmpeg2theora -p pro

[Conrad Parker]

Hi Peter,

I think that the problems you're seeing are due to buffering
requirements imposed by the stream. The file is legal Ogg (at least,
it passes oggz-validate) but if the Ogg pages had been constructed
differently then the buffering requirements would be smaller. This is
something we should look at fixing in ffmpeg2theora and/or libogg.

On a faster machine with 2GB RAM, the p_pro.ogg file plays ok (in vlc,
xine and mplayer) -- which isn't to say you should get a beefier
machine, just saying that the file is not corrupt or invalid.

The following is an analysis of that stream to help us improve pagination:

1. Here's a 'hogg pagedump' of the file:
http://snapper.kfish.org/~conrad/tmp/p_pro_dump.txt

A couple of things are noticeable in that: firstly there are long
stretches of only Theora pages (up to 20 or so in a row in some parts)
in between Vorbis data. If instead, Vorbis pages were flushed more
often, then the buffering requirements would be smaller.

Secondly, almost every page ends with an incomplete packet, which
means that the timestamping is often deferred. This may make correct
audio/video sync harder than necessary for players. If instead Theora
pages were flushed at the end of each packet, then the file would
contain more timestamps (and fewer packets would be unnecessarily
split across page boundaries).

2. This is the output of dump-stream-sync-info (a debug tool from liboggplay):

========================================
Reading 2 tracks ...
        Theora: Track 0 ... ok ...
        Vorbis: Track 1 ... ok ...
Total 3594 frames.

Theora: Track 0
        Worst overrun: 32
        Average overrun: 6.105
        Histogram bucket size: 1.600
        Histogram: 259 724 356 703 345 642 397 58 40 11 14 12 6 12 7 1 2 1 2 2
        SD of overrun: 3.605551

Vorbis: Track 1
        Worst overrun: 47808
        Average overrun: 9224.708
        Histogram bucket size: 2390.400
        Histogram: 449 485 624 450 474 569 319 106 21 12 12 16 7 9 12 8 5 7 4 5
        SD of overrun: 6248.535828
========================================

The worst overruns are in the order of a second. If the players in
question decode frames immediately on demux (and hence queue decoded
frames) then we are looking at a potential queue of many MB of image
data, which could explain the observed sync issues.

Thanks for the file!

cheers,

Conrad.

On 25/05/07, Peter Colton <theora at bissybox.com> wrote:
>
>         Hello Conrad and thanks,
>
> wget www.bissybox.com/p_preveiw.ogg
>
> wget www.bissybox.com/p_pro.ogg
>
> The p_pro.ogg file play a little better with kaffeine than vlc.
>
> I have used ffmpeg2theora-0.18.linux.bin.bz2 and had the same problem
>
>         Regards
>
>                 Peter Colton
>
> admin at apt-get:/mnt/data$ ffmpeg2theora -p preview
> vob-file.vob -o -p_preveiw.ogg
> Input #0, mpeg, from 'CHAVEZ1-1.vob':
>   Duration: 00:52:51.6, start: 0.078678, bitrate: 9328 kb/s
>   Stream #0.0[0x1e0]: Video: mpeg2video, yuv420p, 720x480, 9000 kb/s, 29.97
> fps(r)
>   Stream #0.1[0x80]: Audio: ac3, 48000 Hz, stereo, 192 kb/s
>   Pixel Aspect Ratio: 1.00/1   Frame Aspect Ratio: 1.33/1
>   Resize: 720x480 => 320x240
> No accelerated IMDCT transform found
>       0:02:00.58 audio: 75kbps video: 167kbps
>
> admin at apt-get:/mnt/data$ ffmpeg2theora -p pro vob-file.vob -o -p_pro.ogg
> Input #0, mpeg, from 'CHAVEZ1-1.vob':
>   Duration: 00:52:51.6, start: 0.078678, bitrate: 9328 kb/s
>   Stream #0.0[0x1e0]: Video: mpeg2video, yuv420p, 720x480, 9000 kb/s, 29.97
> fps(r)
>   Stream #0.1[0x80]: Audio: ac3, 48000 Hz, stereo, 192 kb/s
>   Pixel Aspect Ratio: 0.89/1   Frame Aspect Ratio: 1.33/1
>   Resize: 720x480
> No accelerated IMDCT transform found
>       0:02:00.20 audio: 101kbps video: 1869kbps
>
>
> On Friday 25 May 2007 04:28, you wrote:
> > On 25/05/07, Peter Colton <theora at bissybox.com> wrote:
> > > The problem I am having is when I encode a .vob with " ffmpeg2theora -p
> > > pro ". The resulting .ogg will not play correctly with vlc or  kaffeine.
> > > The vedio is jerky and the sound go out of sycro just after the start of
> > > the video. The video veiwer takes up all the cpu resourses for the .ogg
> > > when encoded with " ffmpeg2theora -p pro ".
> >
> > Hi,
> >
> > any chance you could post say the first few MB of such a file
> > somewhere? I've got a hunch it has something to do with the way the
> > audio and video tracks are interleaved and timestamped (forcing the
> > players to buffer much more than necessary), but I'm not sure ...
> >
> > cheers,
> >
> > Conrad.
>
>