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

[Víctor Paesa]

Hi,

Michael Niedermayer said:
> 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?

I recall vaguely a problem involving reading from a VOB with NAVs using
vcodec copy that would fail to pass on the proper number of NAVs.

I'll try to find it.

Regards,
V?ctor