Re: [Libquicktime-devel] More patches

[Joseph A. <jo...@mi...>]

On 20/11/2012 08:58, Joseph Artsimovich wrote:
> On 19/11/2012 17:24, Burkhard Plaum wrote:
>
>> ...
>>
>>    From what I see right now, the lines:
>>
>>        codec->avctx->time_base.den = lqt_video_time_scale(file, track);
>>        codec->avctx->time_base.num = lqt_frame_duration(file, track, NULL);
>>
>> should in any case become:
>>
>>        codec->avctx->time_base.den = lqt_video_time_scale(file, track);
>>        codec->avctx->time_base.num = 1;
>>
>> and (citing Michael Niedermayer):
>>
>> "if one would set timebase = 1/600 THEN pts would go 0 24 48 ..."
>>
>> which would also be libquicktime's idea of PTSes in a 600/24 fps stream.
>> Either I completely overlooked something, or the 1 line change above is enough.
> OK, I'll try to implement that strategy.
>
It doesn't look like it's going to work. When I set the following:

codec->avctx->time_base.num = 1;
codec->avctx->time_base.den = lqt_video_time_scale(file, track);
codec->avctx->ticks_per_frame = lqt_frame_duration(file, track, NULL);

avcodec_open2() then fails with "MPEG1/2 does not support 600/1 fps". It 
doesn't even look at ticks_per_frame.

It also lools like even if you remove that check, 1/600 ratio would get 
written to MPEG bitstream. In fact that's the whole point of 
ticks_per_frame, to be able to put 1/50 to MPEG bitstream for 50i 
content. So, this behaviour is by design.

The solution I am thinking about is doing what my previous patch did, 
but only for XDCAM. This will make it impossible to generate 
variable-duration XDCAM frames, but I don't expect anyone to ever need that.

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