Its not constrained, that would be ABR.
Pardon the OT, what's the difference between CVBR and ABR in AAC?
Which encoder?
Chris
I thought there was a standard.
All of them? For now let's pick only Apple, FhG and FhG FDK.
This is entirely up to the encoder, the exact same decoder can be used for all bit-rate modes. (
Edit: except maybe in case of some streaming decoders which cannot decode VBRish bit-streams).
Generally, such modes describe the order of magnitude of the time duration over which an encoder produces a constant bit consumption for a certain target bit-rate.
Within that duration, the encoder may distribute bits unequally across frame boundaries. The time duration is controlled by the size of the encoder's bit-reservoir.
- Hard CBR: no bit-reservoir, every frame (21.5-43 ms) has the same bit consumption (e.g. -hard-cbr in Opus)
- Soft CBR: small bit-reservoir, for example one with the size given in the MPEG standard (e.g. Fraunhofer CBR)
- ABR: large bit-reservoir, maybe up to a few seconds. Entirely up to the developer (e.g. ABR in Nero's encoder?)
- CVBR: very large bit-reservoir, maybe up to a minute. Entirely up to the developer (e.g. CVBR in Apple's encoder?)
- TVBR: maximum bit-reservoir, every frame and channel may use between ~10 and 6144 bits (e.g. Apple's or Fraunhofer's VBR)
Chris
Awesome, thank you Chris.