[Ffmpeg-devel] Re: Bethsoft VID demuxer and decoder

[Michael Niedermayer]

Hi

On Mon, Mar 26, 2007 at 04:54:08PM -0700, Mike Melanson wrote:
> Michael Niedermayer wrote:
> >this is wrong, you should set the proper timebase (and i suggest you dont
> >look in demuxers written by melanson ;) for figuring our how to do that)
> 
> See, that's why I advised him to direct this patch to the broader list. 
>  All of my demuxers predate the new pts system and I still haven't 
> figured it out. 

whats a timebase?
its simply the units in which timestamps are stored
1 second for example is one, 1/100 second too is one ...

now for example if we have a 25 fps video and a 1/100 second timebase then the
frames could have the following timestamps 
0,4,8,12,16,20,...

if we have a 1/150 second timebase then our 25 fps video would have
0,6,12,18,24,30,...

and a 30 fps video with 1/150 timebase would have
0,5,10,15,20,25,...

if we now have a video with 1/30 fps which has a few identical frames which
have been skiped and arent stored then the timestamps might be
0,5,20,25,...

a 30 and 25 fps mixed video with 1/150 second timebase could look like
0,5,10,15,21,27,33,39,...

av_set_pts_info(AVStream *s, int pts_wrap_bits, int pts_num, int pts_den);

av_set_pts_info() sets the timebase and the number of bits each timestamp has
so if timestamps are stored as 33 bit values like in mpeg then pts_wrap_bits
is 33, if they are stored as 64bit values in the bitstream then its 64
pts_num is the numerator of the timebase, pts_den the denominator

i hope this makes the whole clear to everyone ...


> How I rose to be the FFmpeg mentoring administrator is 
> anyone's guess. :)

you volunteered ;)
and handled last years soc excellently btw ...

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

No human being will ever know the Truth, for even if they happen to say it
by chance, they would not even known they had done so. -- Xenophanes
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