The VideoLAN Forums

This is a very serious request. I know many people consider CBR as an outdated bitrate management method.
However if the statistics panel is accurate (Ctrl-I), i can't get any stable bitrate when streaming live.
I've tried averything i could think of.
qcomp=O doesn't change anything for me. Setting bitrate variability do 0 in the vfw panel version doesn't either.
Even at these settings, i still get peak bitrate of 800kbps and beyond for my 400kbps stream.

Some people suggested increasing the Min QP value which will only result in poorer quality in areas where my target bitrate would have been suficient.
In fact, i'm under the impression that min and max QP settings prevail above all other settings, especially bitrate variability.
In the bitrate based setting, wouldn't it be logical that with bitrate variability set to 0, the stream would stay close to the given bitrate, overiding any of the QP settings ?

Am i wrong to assume that with bitrate variability set to 0 (same as qcomp=0 i believe), the resulting stream would be CBR ? From my experience, this is obviously not the case. Would i have better luck with vbv-maxrate ?

We need a way to ensure that the bitrate will be strictly limited to a max given value for certain applications such as streaming.
Why not a VBR mode in which we could input min, average and absolute max bitrate values ?
Anyway, i still believe broadcasters need a true CBR mode.

We need a way to enforce a given bitrate. How is one supposed to stream at 450kbps on a 800kbps line if values skip to 900kbps all the time ?
I'm not against VBR as long as it's not acting crazy. If i want quality, i use the single pass - Quantizer mode, not the single pass - bitrate mode. I think the latter should be used for environments needing strict bitrate control.
Vorbis quality based bitrate management as always worked well for me since fluctuations are always very subtle. I need something as reliable for x264.

Would that be very hard to implement ?

Thank you for reading this.

No x264 devs read this forum You should ask the question on the mailing list or on one of the forums listed on http://x264.nl

Thanks for the tip.

Leave out the qp, qp-min and qp-max values because those indeed will take precedence over specifiying a max bitrate, it takes whatever bitrate it needs to maintain quality.

If you want something resembling CBR you can specify bitrate like this: vcodec=h264,venc=x264{vbv-maxrate=800,etc.},vb=800,etc. where vb is the average bitrate, and vbv-maxrate is the maximum which in this case is the same...

Hello folks,

We are also facing certain problems related to fluctuating bitrates by VLC. I would like to know in particular is VideoLan developers have taken a note of this allready? Can anyone lead me to the ticket / track No. where the bug related to such fluctuations is accepted.

looking forward for a prompt reply.

Regards
Rahul Sharma

Try using qcomp=0.01

I'm still trying to stream live h264 from a windows machine. I'm still puzzled by this bitrate management issue.

Again, what parameters would you suggest ? I tried the suggested options to no effect.

I know most modern codecs rely heavily on VBR for quality. Some developpers don't even want to hear about CBR anymore.
I heard about the qcomp=0 parameter within x264. Here's what i've tried so far :

:sout=#transcode{vcodec=h264,venc=x264{vbv-maxrate=512,qcomp=0,ratetol=0}vb=512,scale=1,acodec=mp4a,ab=64,channels=2}:duplicate{dst=std{access=file,mux=ts,dst="C:\Documents and Settings\Admin\Desktop\test5.ts"}

I input these in the "flux" field of the GUI. This SHOULD give me precise control over the desired bitrate. Well it doesn't.

When checking the bitrate during playback, it still hops way above my network capabilities.

Any help would be REALLY apreciated.
I know many people are interested in this as well.