[FFmpeg-devel] [RFC][PATCH] ticks_per_frame / timebase

[Ivan Schreter]

Michael Niedermayer wrote:
> On Fri, Feb 27, 2009 at 06:47:42PM +0100, Ivan Schreter wrote:
>   
>> Ivan Schreter wrote:
>>     
>>> Michael Niedermayer wrote:
>>>   
>>>       
>>>> On Fri, Feb 27, 2009 at 09:54:36AM +0100, Ivan Schreter wrote:
>>>>       
>>>>         
>>>>> Michael Niedermayer wrote:             
>>>>>           
>>>>>> good, ive applied it, if you find more regressions please tell me
>>>>>>
>>>>>>                 
>>>>>>             
>>>>> TS works without problem.
>>>>>
>>>>> However, there is a regression with MOV. I tried to decode trailer for 
>>>>> movie "9", which is H.264 progressive 23.98 fps, but it detects it as 
>>>>> 11.99 fps:
>>>>>           
>>>>>           
>>>> that happens because of local changes in your tree, i suspect the hunk
>>>> to the r_frame_rate code i rejected
>>>>
>>>>       
>>>>         
>>> I looked at the changes before reporting it. But you are right, there was 
>>> one hunk where I removed H264 from tb_unreliable. This was the reason.
>>>
>>> OTOH, when reverting this hunk, interlaced field-picture H.264 stream is 
>>> detected at 2*fps... I'll check it later, but I don't think it's because 
>>> of my local changes (only seeking changes are there).
>>>
>>>   
>>>       
>> So, now I looked at it. The problem is, the information repeat_pict and 
>> ticks_per_frame is not enough to determine frame duration for tb_unreliable 
>> H.264 stream.
>>
>> So we have following values for these MPEG-TS H.264 streams:
>>
>> Progressive: ticks_per_frame == 2, repeat_pict == 1, dts deltas == frame 
>> duration.
>> Interlaced, field-pictures: ticks_per_frame == 2, repeat_pict == 0, dts 
>> deltas == 1/2 frame duration.
>> Interlaced, top-bottom pictures: ticks_per_frame == 2, repeat_pict == 1, 
>> dts deltas == frame duration.
>>
>> All of these use timebase 2*fps.
>>
>> However, for H.264 MOV stream (progressive) we have timebase == fps!
>>     
>
> nope, thats whats printed, but a av_log() in h264.c shows the timebase
> is 2*fps for my sample
>   
Independent of that, frame rate is computed wrong for field picture 
stream, since only field durations are taken into account. So I think 
the patches for field flag should be applied (or it must be fixed in a 
different way, but how?).

As for the MOV, my MOV is missing timing info! I just noticed now 
(timing_info_present_flag == 0). So at least in this case, it doesn't 
work. Attached patch sets ticks_per_frame to 2 only if time_base is 
specified. If it is unknown, lavf will set it equal to frame rate, so 
then ticks_per_frame is 1 (default)...

Regards,

Ivan

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