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

[Víctor Paesa]

Hi,

Michael Niedermayer dijo:
> Hi
>
> On Sun, Jul 15, 2007 at 10:39:07AM +0200, V?ctor Paesa wrote:
>> Hi,
>>
>> V?ctor Paesa said:
>> > 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.
>>
>> Here it is:
>> http://thread.gmane.org/gmane.comp.video.ffmpeg.user/8662
>
> does it work if the above mentioned align_iframe = 0 is removed?

Yes, it worked: all the 160 NAV packets were passed on (the scenario is
the worst case at the previous to last mail in that thread).

Regards,
V?ctor