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

[Baptiste Coudurier]

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.

-- 
Baptiste COUDURIER
Key fingerprint                 8D77134D20CC9220201FC5DB0AC9325C5C1ABAAA
FFmpeg maintainer                                  http://www.ffmpeg.org