[FFmpeg-devel] [PATCH] H.264 timestamps in h264_parser - complete set

[Ivan Schreter]

Michael Niedermayer wrote:
> On Fri, Feb 20, 2009 at 08:46:29PM +0100, Ivan Schreter wrote:
>   
>> Michael Niedermayer wrote:
>>     
>>> On Fri, Feb 20, 2009 at 06:52:30PM +0100, Ivan Schreter wrote:
>>>   
>>>       
>>>> Michael Niedermayer wrote:
>>>>     
>>>>         
>>>>> On Fri, Feb 20, 2009 at 04:00:34PM +0100, Ivan Schreter wrote:
>>>>>   
>>>>>       
>>>>>           
>>>>>> Michael Niedermayer wrote:
>>>>>>     
>>>>>>         
>>>>>>             
>>>>>>> On Fri, Feb 20, 2009 at 03:30:16PM +0100, Ivan Schreter wrote:
>>>>>>>         
>>>>>>>               
>>>>>> That was also my question in another post - where do I get the clock in 
>>>>>> lavc?
>>>>>>     
>>>>>>         
>>>>>>             
>>>>> do you really need it?
>>>>>   
>>>>>       
>>>>>           
>>>> Not for convergence, since we can express it via frame count. But for 
>>>> pts/dts computation, definitely. For H.264 case, the stream must have 90kHz 
>>>> clock according to H.264 standard, so it should be OK. But for other 
>>>> codecs, I don't know.
>>>>
>>>> Alternative would be to scale pts/dts to some common unit (e.g., 
>>>> 1/1000000th second) and then rescale back.
>>>>     
>>>>         
>>> the container timebase in which pts/dts are specified is not
>>> guranteed to be 90khz, even if h264 says it is so, it just isnt in practice.
>>> things may work out because only mpeg-ps/ts ommit pts/dts "randomly" and
>>> mpeg-ps/ts have 90khz but .mp4/mov/nut/mkv do normally not use 90khz timebase
>>>
>>>   
>>>       
>> True, I downloaded some MOV AVCHD trailers and they don't work with 
>> timestamping code correctly. Seem to use 1MHz clock, or so.
>>
>>     
>>> also rounding is not ok
>>>
>>>   
>>>       
>> We'll need to communicate proper timebase for timestamping from lavf to 
>> lavc in AVCodecParserContext, then, so it can compute timestamps correctly.
>>     
>
> hmm i think the parser should export its dts/pts correction in 
> AVCodecContext.time_base units (i think this is the correct one)
> and the code in lavf should then merge that into its dts/pts
>
>   
The problem is, the timestamps are not integer multiples of time_base. 
Not even the difference between them is an integer multiple - for 
interlaced field picture movies, the timestamps of second field are 
offset by 1/2 frame duration. So integer is not sufficient there. 
Furthermore, current context already gets "real" pts/dts from lavf, 
which only needs to be adjusted.

BTW, AVCodecContext.time_base is something like 1/25 (i.e., frame rate).

So I feel passing time base to lavc when initializing parser makes it 
easier.

The timestamps in H.264 will not diverge, since we use container's 
timestamp (wherever available) as reference.

So I was thinking about something like attached patch, which then 
provides container_time_base to the parser. With this, I could get rid 
of hard-coded 90kHz time base in H.264 timestamps calculation and it now 
works for MOV as well.

OK so?

Regards,

Ivan

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