[FFmpeg-devel] [PATCH] Fix ratecontrol bug when time_base.num > 1

[Michael Niedermayer]

On Fri, Nov 16, 2012 at 05:20:16PM +0000, Joseph Artsimovich wrote:
> On 16/11/2012 16:44, Michael Niedermayer wrote:
> >On Fri, Nov 16, 2012 at 04:24:30PM +0000, Joseph Artsimovich wrote:
> >>On 16/11/2012 16:11, Michael Niedermayer wrote:
> >>>On Fri, Nov 16, 2012 at 04:01:26PM +0000, Joseph Artsimovich wrote:
> >>>>On 16/11/2012 15:28, Kieran Kunhya wrote:
> >>>>>>I dont fully understand the problem, so its hard to suggest how to
> >>>>>>fix it.
> >>>>>The problem is his application doesn't like the timebase as a reduced
> >>>>>fraction, but would rather
> >>>>>have it as a reducible fraction.
> >>>>>
> >>>>Not quite. That's only part of the problem. The following line of
> >>>>code from ratecontrol.c:
> >>>>
> >>>>wanted_bits = (uint64_t)(s->bit_rate*(double)dts_pic->f.pts / fps);
> >>>>
> >>>>won't work correctly for any time_base where numerator is greater
> >>>>than 1, as it doesn't consider the scale of dts_pic. For instance,
> >>>>it will fail on your typical NTSC timing of 1001/30000. Now, the
> >>>>obvious fix is to include s->avctx->time_base.num into the
> >>>>denominator of the above line of code. That would fix the NTSC case,
> >>>>but not my case, which was 24/600, as s->avctx->time_base gets
> >>>>automatically reduced to 1/25. Therefore, I went with s->dts_delta
> >>>>instead of s->avctx->time_base.num. However, Michael explained it's
> >>>>not suited for that purpose.
> >>>fps is calculated as 1.0 / av_q2d(avctx->time_base) / FFMAX(avctx->ticks_per_frame, 1);
> >>>that is supposed to take the numerator already into account.
> >>>
> >>>also 24/600 or 1/25 the timestamps should be 1,2,3,4,...
> >>Note that we are talking about user-provided timestamps. I use
> >>libavcodec indirectly through libquicktime, which in my case sets:
> >>avctx->time_base.num = 24;
> >>avctx>time_base.denum = 600;
> >>avframe->pts = 0, 24, 48, ...
> >     /**
> >      * presentation timestamp in time_base units (time when frame should be shown to user)
> >      * If AV_NOPTS_VALUE then frame_rate = 1/time_base will be assumed.
> >      * - encoding: MUST be set by user.
> >      * - decoding: Set by libavcodec.
> >      */
> >     int64_t pts;

> Does that mean pts always goes 0, 1, 2, ...? If so, that's a problem
> with libquicktime not with ffmpeg.

if one would set timebase = 1/600 THEN pts would go 0 24 48 ...


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

Good people do not need laws to tell them to act responsibly, while bad
people will find a way around the laws. -- Plato
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