[FFmpeg-devel] Google Summer of Code participation

compn tempn
Sat Mar 28 20:59:24 CET 2009

On Sat, 28 Mar 2009 18:46:46 +0100, Vitor Sessak wrote:
>Thilo Borgmann wrote:
>> Kostya schrieb:
>>> On Sat, Mar 28, 2009 at 12:20:32PM +0100, Thilo Borgmann wrote:
>> Ok next problem arises. I'm currently trying to distinguish the I and P 
>> frames to be decoded.
>> As you mentioned, I tried to check the keyframe flag, that comes from 
>> 'outside'.
>> For that, I "av_log"ed the "key_frame" and "pict_type" attributes:

>> (source listing is highly mailing list dependent - tell me how you like 
>> it if this is a pain in your eyes)

probably attached as plain .txt for larger pieces
a few lines inline isnt so bad, but i cant speak for all...

>> As these debug outputs are telling that every frame is a key frame, 
>> which most of them are not, the question is if I'm looking at the wrong 
>> attributes or if this information is not parsed at all?
>There are three possibilities:
>1- This information is coded somewhere in the AVI format (and thus it is 
>the work of the AVI demuxer to read it and set the parameters).
>2- This information is in some reserved bits of the PNG stream (and so 
>it is in pngdec.c that it should be read).
>3- This information is nowhere and the codec follow some stupid 
>convention like one frame every X are key-frames.
>I suggest you to look in the available documentation/source code to know 
>where this information is supposed to be. I find (1) unlikely since 
>ffmpeg AVI demuxer is not so buggy, and it would set picture->key_frame 

an easier way is to use the corepng encoder to create some file which
you can control the encoding options. e.g. make a file with all
keyframes, then a file with no keyframes so you can analyze the

this will also let you know if ffmpeg is detecting the frames correctly.


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