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Topic: Difference between CVBR and ABR in AAC (Read 8787 times) previous topic - next topic
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Difference between CVBR and ABR in AAC

Its not constrained, that would be ABR.

Pardon the OT, what's the difference between CVBR and ABR in AAC?

Difference between CVBR and ABR in AAC

Reply #1
Which encoder?

Chris
If I don't reply to your reply, it means I agree with you.

Difference between CVBR and ABR in AAC

Reply #2
I thought there was a standard.

All of them? For now let's pick only Apple, FhG and FhG FDK.

Difference between CVBR and ABR in AAC

Reply #3
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
If I don't reply to your reply, it means I agree with you.

Difference between CVBR and ABR in AAC

Reply #4
Awesome, thank you Chris.