h264 constant sample size?

[terryleung]

Hi all,

I am doing a project which require to have constant sample size in h264 video
However, I've tried ffmpeg with x264, but with no luck

./ffmpeg -i 1.mp4 -acodec copy -vcodec libx264 -qcomp 0 -b 150000 2.mp4


I've seen that there is a qcomp=0 option which can make video have constant bitrate. However, it doesnt work

anyone have any idea?

[Ranguvar]

http://forum.doom9.org/showthread.php?t=102893
http://forum.videolan.org/viewtopic.php?t=21961

[terryleung]

Hi Ranguvar,

Thanks for your reply

I've just try to use those method
the -bt(ratetol=0) is not working (invalid value)

so I've tried

./ffmpeg -i 1.mp4 -acodec copy -vcodec libx264 -vframes 100 -qmin 1 -qmax 51 -qcomp 0.00 -bt 1 2.mp4

But it is still not having constant sample size
Maybe I am doing something wrong.

However, according to my understanding, those thread are related to bitrate control
which is slightly different with my case
what i want is to made every sample the same size(or at least every iframe have the same size and every pframe have the same size) without using padding bit

[Dark Shikari]

qcomp does not have any real relation to constant bitrate, nor does bt.

x264 does not support absolute constant framesize, nor do I know any encoders that do. H.264 is an inherently variable bitrate format, and "CBR" in H.264 is defined by a buffer size.