-flags -cgop deon not work with me

[abeer]

hi:
I need to compress a video with close GOP and open Gop to compare them using some algorithm.
I used -flags -cgop for open and -flags +cgop for close with GOP=12, and gets the same pattern
IBPBPBPBPBPP for both open and close...... I think the pattern must be for open IBPBPBPBPBPB, the pattern must ends with B-frame...
please help me

ffmpeg -i vid.y4m -vcodec libx264 -g 12 -flags -cgop -y -r 30 output.avi 2>list4.txt

[Selur]

a. if your ffmpeg version is more than 20month old http://ffmpeg.org/trac/ffmpeg/ticket/261 might be a problem.
b. open and close gop do not always have different frame patterns (e.g. scene change detection might trigger a IDR frame for both)
c. no clue where you get the assumption that the frame pattern must end with a B-Frame for open gop,...
d. compiling x264 with lav support and simply using the x264 encoder directly might give better control over the x264 parameters,...

[abeer]

i read this
http://documentation.apple.com/en/compressor/usermanual/index.html#chapter=18%26sectio...5%26tasks=true
the last P-frame is replaced with B-frame that depends on the I-frame of the next GOP

[Selur]

a. that is for mpeg-2
b. that would be for a quicktime encoder
-> not really valid if you are neither using MPEG-2 nor the encoder this documentation is written for

[abeer]

sorry Im new in using ffmpeg, can u please rewrite my command to make it use quivktime encoder

[Selur]

it's ffmpeg and not a Quicktime/Apple tool so it can't use their encoder,... if you want to use encoder that comes with Compressor 3 ( or 4) you need to use a Mac and FinalCut.

[abeer]

what about this
libx264: change default to closed gop to match x264cli

open-gop can be enabled with "-flags -cgop"
http://lists.libav.org/pipermail/libav-commits/2012-September/008145.html

[Selur]

what about this

Sorry, I don't see a connection to my posts.

My point (in post #4) was only that if you use x264 (or any other H.264 codec) you can't rely on documentation for a MPEG-2 encoder of Apple!
I only wrote that I think that the assumption that gops need to end with b-frames is wrong and that if you want to rely on the documentation you linked to you should use the encoder the documentation belongs to,...

Before (in post #2) at the beginning was, that if -flags -/+cgop doesn't work for you it might be due to an old ffmpeg version,...

=> no clue what you are trying to tell me with your last post.

Cu Selur

[El Heggunte]

Just for the notes (and according to my understanding of the subject):

-- if an open-GOP begins with a B-frame, then it ends with a P-frame (or even on an I-frame)

-- if an open-GOP begins with an I-frame, then it ends with a B-frame

-- ffmpeg does not / cannot fully~control the behavior of the codecs which are not part of the libavcodec bundle

-- until some years ago at least, the only ways to ensure closed-GOPs through ffmpeg were: 1) not use B-frames, or 2) disable the scene-detection algorithm.

[abeer]

I just want to ensure that this is true (what is written in link), I dont be to bother you.... I just want your help

[Selur]

ah okay, yes the info in the link should be true.

[abeer]

i have another problem, I libx264 does not take the bit rate I choos into consideration, what to do?

[Selur]

Read up on how to use libx264 properly.
Especially the difference between the different 1pass and 2pass rate control methods.

[abeer]

I used this command
ffmpeg -i vid -vcodec libavcodec -b:v 300k -target pal-vcd -g 15 -bf 2 -y -r 30 output4.h264 2>list5.txt

[abeer]

ffmpeg -i vid.y4m -vcodec libavcodec -b:v 300k -target pal-vcd -g 15 -bf 2 -y -r 30 output4.h264 2>list5.txt
I wrote it like this to get 2 B-frames

[Selur]

Now you lost me.
You wrote you have problems using libx264 and then you post a command line which created mpeg-1 video.
-> you really should read a bit more about ffmpeg&libx264 if you want to use it.

[abeer]

sorry instead of libavcodec , it must be libx264, its not the line code I wanted

[Selur]

if you use libx264 the '-target pal-vcd' still doesn't make ANY sense,... -> read the ffmpeg documentation/manual if you want to use ffmpeg