[FFmpeg-devel] [PATCH] decode at least 4 H.264 frames in av_find_stream_info

[Baptiste Coudurier]

On 6/27/10 3:34 PM, Michael Niedermayer wrote:
> On Sun, Jun 27, 2010 at 02:18:18PM -0700, Baptiste Coudurier wrote:
>> On 6/27/10 7:09 AM, Michael Niedermayer wrote:
>>> On Sun, Jun 27, 2010 at 12:39:13AM -0700, Baptiste Coudurier wrote:
>>>> On 6/26/10 7:43 PM, Michael Niedermayer wrote:
>>>>> On Sun, Jun 27, 2010 at 04:31:41AM +0200, Michael Niedermayer wrote:
>>>>>> On Thu, Jun 24, 2010 at 05:44:20PM -0700, Baptiste Coudurier wrote:
>>>>>>> Hi guys,
>>>>>>>
>>>>>>> $subject.
>>>>>>>
>>>>>>> This will permit the decoder to compute has_b_frames correctly when
>>>>>>> b-pyramid is present. 4 is typically the minimum needed, though maybe
>>>>>>> we
>>>>>>> should decode more based on has_b_frames. Any opinion ?
>>>>>>
>>>>>> Finally found an old patch by myself doing this
>>>>>> I think its a bit more readable
>>>>>> if it works feel free to apply mine (assuming that thing still applies
>>>>>> and
>>>>>> works)
>>>>>
>>>>> ehm, the patch:
>>>>>
>>>>> Index: libavformat/utils.c
>>>>> ===================================================================
>>>>> --- libavformat/utils.c	(revision 18646)
>>>>> +++ libavformat/utils.c	(working copy)
>>>>> @@ -1820,6 +1820,12 @@
>>>>>     #endif
>>>>>     }
>>>>>
>>>>> +/*we need to find has_b_frames approximatly, the parser is not yet able
>>>>> to do it*/
>>>>> +static int has_decode_delay_been_guessed(AVCodecContext *enc)
>>>>> +{
>>>>> +    return enc->codec_id != CODEC_ID_H264 || enc->frame_number>= 4 +
>>>>> enc->has_b_frames;
>>>>> +}
>>>>
>>>> I'm not sure about enc->frame_number, now that st->codec_info_nb_frames
>>>> is
>>>> used in av_find_stream_info, it seems the best field to use.
>>>
>>> hmm, i dont think theres a difference currently between using these 2
>>> though they are semantically a bit different. So use what you prefer
>>>
>>>
>>>>
>>>> Your patch is not enough I think, you need to always call
>>>> try_decode_frame
>>>> even if has_codec_parameters is true.
>>>
>>> calling it for the first 4 frames with h264 is ok
>>> calling it unconditionally always would slow av_find_stream_info() down
>>> quite
>>> a bit i think
>>>
>>
>> This is code in svn:
>>
>>          if (!has_codec_parameters(st->codec))
>>              try_decode_frame(st, pkt);
>>
>> I meant the check has to be removed, otherwise only one frame will be
>> decoded.
>
> what about:
>
> if (!has_codec_parameters(st->codec) || !has_decode_delay_been_guessed())
> ?

Why duplicating the check ? This check is also in try_decode_frame, so 
either one can be removed.

-- 
Baptiste COUDURIER
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