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

[Michael Niedermayer]

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())
?

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

it is not once nor twice but times without number that the same ideas make
their appearance in the world. -- Aristotle
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