[Libav-user] How FFMPEg or x264 pars the I-Frames (IDR or non IDR)

Jaroslav Korchevsky jslav at mail.ru
Sat Apr 30 07:25:26 CEST 2011

In VCL videoslice header there is a Variable Length coded field SliceType.
Types 2,4,7,9 - correspond to I-frames

Fri, 29 Apr 2011 11:49:42 +1000 письмо от Amir Rouhi-Rmit <amir.rouhi at rmit.edu.au>:

Those who has worked deeply with FFMPEG should know the answer of my question. My question is that :
how the software find I-Frame by parsing bit-stream of the input video. Can the software( FFMPEG, X264) can differentiate IDR and non IDR I-Frames? 
Probably yes, in that case what's the starting word bit stream of these two type of I-Frames? Some people believe that IDR I-Frames starting bit stream is 00 00 00 01 y in hex which (y=25, 45, 65). Are you agree with this?
According to H.264 standard chapter 7 and annex B, The three byte start code bit-stream  00 00 01 is correct for starting VCL NAL units. But the one Byte header which start with 0, the rest of 7 bits can not be 0 if the picture is IDR. I confused, please somebody advise.

Amir H. Rouhi 
PhD Student/ CSIT RMIT University 
Room: 14-09-04 
rouhi_amirhossein at student.rmit.edu.au 
amir.rouhi at rmit.edu.au 
Libav-user mailing list
Libav-user at ffmpeg.org

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