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

[Amir Rouhi-Rmit]

Hi
Would you explain more clearly? As far as i know in VCL NAL units we have a
3 byte start code prefix which startwith 0x00 00 01. after that we have a
byte which the first most significant bit (the most left bit) should be
zero, the next two bits are nal_ref_idc which for I-Frames should not be
zero, and the last 5 bit which are called nal_unit_type, they can be a
number from 1 to 32. for frames they can be 1 to 5. ant it seems for
i-frames the value of these 5 bit should be 5 according to standard. I would
be pleased if you explain more about the values of 2,4,7,9 which u believe
are i-frame codes..

On Sat, Apr 30, 2011 at 3:25 PM, Jaroslav Korchevsky <jslav at mail.ru> wrote:

>
>
> 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<http://sentmsg?compose&To=rouhi_amirhossein@student.rmit.edu.au>
> amir.rouhi at rmit.edu.au <http://sentmsg?compose&To=amir.rouhi@rmit.edu.au>
>
>
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-- 
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
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