[Ffmpeg-devel] wrong framerate in mpeg4 file?

[Ivo]

On Friday 23 September 2005 20:42, Luca Ognibene wrote:
> Il giorno dom, 18/09/2005 alle 14.54 +0200, Luca Ognibene ha scritto:
> > hi!
> > I have a problem with some mpeg4 files.
> > ffmpeg reports that they have a framerate of 3000fps.
>
> With this file:
> In h263.c:decode_vol_header reads 3000 in time_base.den and set
> time_base.num to 1 because get_bits1(gb) returns 0.
> With a older version of ffmpeg the fps reported would be 29.97 but now
> it's 3000.
>
> Is 1/3000 a special value? How can i know if time_base is valid or not ?
>
> thanks for your help.

That's "funny". I just spend three hours yesterday tracking this down. I had 
missed your original posting and I was playing with the -demuxer 35 (lavf) 
option of mplayer :-) Well, I learned a lot of lavc/lavf's internals, so it 
was not a complete waste of time.

Anyway, I have several avi's (from different sources) that play at 
24000/1001 and 25000/1000 fps with mplayer's native demuxer, but play at 
30000/1 fps with lavf's demuxer (well, it tries to :) ). I tracked it down 
to exactly the same point you did, namely decode_vol_header() in h263.c.

I'm not sure if it should restore avctx->time_base.den and time_base.num 
instead of setting .num to 1, or that the calling application (in "my" case 
demux_lavf) should act upon .num being 1. I've only tried the latter. If 
codec->time_base.num == 1, use st->time_base instead (which is the desired 
25000/1000, 24000/1001, etc.).

Can anybody shed a light on this?

--Ivo