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

[Joseph Artsimovich]

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.
What about dts_delta in MpegEncContext not being 1 then?

-- 
Joseph Artsimovich
Senior C++ Applications Developer
MirriAd Ltd