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Opus - CBR or VBR ?

CBR - Constant Bit Rate
VBR - Variable Bit Rate
Topic: Opus - CBR or VBR ? (Read 3334 times) previous topic - next topic
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Opus - CBR or VBR ?

Just wondering what you guys use. I personally use CBR

Re: Opus - CBR or VBR ?

Reply #1
VBR, I'd only ever use CBR if there's some technical reason that prevents me from using variable bitrate.

Re: Opus - CBR or VBR ?

Reply #2
From the spec: "Opus is more efficient when operating with variable bitrate (VBR), which is the default."

SILK (low bitrate/speech) is specifically designed for VBR, and the CBR setting is very much bolted on. CELT (music/high bitrates) is designed as a CBR codec, but is capable for varying the bitrate frame by frame so it operates seamlessly in VBR mode. With the encoder features for detecting transients and tonality that require additional bitrate to avoid audible artifacts, VBR is always preferable. CBR is included for certain applications that require fixed frame sizes or frame sizes that do not depend on the input signal (eg. encrypted streams). Constrained VBR mode is recommended for low-latency transmissions over slow connections, and simulates a bit-reservoir codec like AAC although it doesn't need to formally use a bit reservoir.

Re: Opus - CBR or VBR ?

Reply #3
Using CBR makes sense in pretty much only just one scenario: non-linear live mixing.

Things like DJ-ing or other live performances. However in those cases memory doesn't seem to be much of an issue and people simply use lossless or 320kb/s MP3s in CBR mode, because some of the tech isn't exactly bleeding edge.

In all other cases: VBR it is.

Re: Opus - CBR or VBR ?

Reply #4
Using CBR makes sense in pretty much only just one scenario: non-linear live mixing.

Things like DJ-ing or other live performances. However in those cases memory doesn't seem to be much of an issue and people simply use lossless or 320kb/s MP3s in CBR mode, because some of the tech isn't exactly bleeding edge.

In all other cases: VBR it is.

Why is that? Can you explain further?

Re: Opus - CBR or VBR ?

Reply #5
Why is that? Can you explain further?

Dedicated DJ-ing equipment has a hard time looking ahead and back in streams where there was a disparity between actual playing time and compressed chunk. When doing live mixing, timing is of an essence, so much so that it is a bigger advantage having a constant bitrate, so each chunk, translates to a fraction of time, and vice versa.

Seeking inside a file that is encoded in CBR is much easier and henceforth quicker, which results in minimal delays. Because of that it is possible to use a file similar to a record. This becomes very important for live performances, not only in clubs where a DJ just plays music, but where sampling and playing files is part of a live song performance, or when it's broadcast.

At the very least these things might not exactly be noticeable by the audience, but by the performer. This might sound a bit "entitled", but the point is, that having low latency systems like this reduces errors and hence frustration on the performer's side (which might lead to more errors).

 
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