I'd like to use OGG@64kbps as an output format (for low data consumption). I'm currently writing an audio streaming client, and I need the estimated data size before streaming. It would be great if the prediction could be accurate to within a few kB. Is it possible to set up ffmpeg or SoX to encode into Ogg/CBR so I can calculate the exact data size?

I agree VBR would be the better option where quality is concerned, but VBR 64kbps doesn't mean that I actually get 64kbps in average. Sadly...

Or would ABR be an option?

Thank you!

  • Opus has a "hard-cbr" option, which acts as true CBR. You can be sure that the bit rate can estimate the size of the overall file.
    – bryc
    Commented Feb 20, 2021 at 17:30

2 Answers 2


I would highly recommend using CELT or Opus for low bitrate audio (48kbps-96kbps), it sounds far superior, even compared to high performance ACC-HE+. the later is an IETF standard, and already widely supported.

Both support CBR, ABR (CVBR), VBR.

Vorbis supports VBR, ABR.

ffmpeg documentation for Vorbis and Opus have easily defined options for ABR control.


Ogg is a VBR codec. but as you seem to know you still can setup a certain bitrate.

Here is what I found on the net

ffmpeg -f alsa -i hw:0,0 -acodec libvorbis -aq 4 -vn audio.ogg

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