[Libav-user] Enquiry about I-Frame rate

[amir.rouhi at rmit.edu.au]

Is there anyone to be able to answer my question?


On 15 February 2012 16:43, <amir.rouhi at rmit.edu.au> wrote:

>
> The scenario is that, I have an .mpg video file. When I extract the
> I-Frames from this file by below command:
>
> ffmpeg -i D:\test\1.mpg -vsync 0 -vf select="eq(pict_type\, PICT_TYPE_I)"
> d:\Test\IFrames\I-Frm-%03d.jpeg
>
>
>
> I will get 104 images which is about an I-Frame for every 12 frames of the
> 1.mpg stream.
>
>
>
> Then I tried to change the video format to MP4 by below command:
>
>
>
> ffmpeg -i D:\test\1.mpg  -vcodec libx264  -g 0 d:\Test\11.mp4
>
>
>
> and
>
>
>
> ffmpeg -i D:\test\1.mpg  -vcodec libx264  -g 10 d:\Test\12.mp4
>
>
>
> the question is that the new generated videos, 11.mp4 and 12.mp4, in spite
> of using different –g values , the I-Frames of these two video is same and
> just is 5 images. I extract them by below command:
>
>
>
> ffmpeg -i D:\test\11.mp4 -vsync 0 -vf select="eq(pict_type\, PICT_TYPE_I)"
> d:\Test\IFrames\I-Frm-%03d.jpeg
>
>
>
> I want to know why there is a  big difference between the mpg and mp4
> files and why in spite of different –g in last two video, I have exactly
> same I-Frames?
>
>


-- 
Amir H. Rouhi
PhD Student/ CSIT RMIT University
Room: 14-09-04
http://raws.adc.rmit.edu.au/~s3288736/blog2/
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