[FFmpeg-devel] Problem with DVD VOB encoding - NAV packets not included properly.

[Michael Niedermayer]

Hi

On Sun, Jul 15, 2007 at 04:09:49PM +1000, Neil Brown wrote:
> 
> Hi,
>  I've been working with kdenlive (which uses the MLT framework which
>  uses the ffmpeg libraries) to make a DVD and found that the VOB
>  created does not have the correct NAV packets.
>  This shows up when I run dvdauthor as it cannot find places to put
>  chapter links, and when viewing the DVD on a DVD player as
>  fast-forward and rewind don't work properly.
> 
>  The "dvd" format is being requested by kdenlive, but the NAV packets
>  don't get produced - well to be fair, a 22 minute VOB had 6 NAV
>  packets rather than the expected 2600 odd.
> 
>  I looked through the code and found that in libavformat/mpegenc.c, in
>  mpeg_mux_write_packet, towards the end, is this code fragment:
> 
>     if (s->is_dvd){
>         if (is_iframe && (s->packet_number == 0 || (pts - stream->vobu_start_pts >= 36000))) { // min VOBU length 0.4 seconds (mpucoder)
>             stream->bytes_to_iframe = av_fifo_size(&stream->fifo);
>             stream->align_iframe = 1;
>             stream->vobu_start_pts = pts;
>         } else {
>             stream->align_iframe = 0;
>         }
>     }
> 
> 
>  If I remove the assignment of 0 to align_iframe in the 'else' clause,
>  the code appears to work.  i.e. I get lots of NAV packets, dvdauthor
>  correctly sets all of the chapter points, and FF/REW works properly
>  in my DVD player.
> 
>  I confess that I only have a shallow understanding of this code, and
>  it could be that my change has some unintended consequences.  I would
>  appreciate if it someone more familiar with the code would check if
>  this is an appropriate change and hopefully get the problem fixed.
> 
>  I am quite happy to test any alternate changes to make sure they
>  still do the right thing on my files if that will help.
> 
>  (Yes, I have checked current SVN code).

if it is reproduceable with (unmodified) command line ffmpeg then please
provide full uncut output + used command line of it

also the code you change is there since 2004, could you try some old svn
versions to check if they generated nav packets properly
and if not then iam a little curious why noone complained yet but ignoring
that, your suggested fix looks correct but i first would like to understand
the issue better also iam not maintainer of the mpeg muxer code, so i wont
approve this change ...

also did nav packet generation/dvd encoding work for anyone?

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

The greatest way to live with honor in this world is to be what we pretend
to be. -- Socrates
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