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Topic: Difference between CVBR and ABR in AAC (Read 4343 times) previous topic - next topic

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  • eahm
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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?
  • Last Edit: 12 January, 2014, 06:32:23 PM by eahm

  • C.R.Helmrich
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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.

  • eahm
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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.
  • Last Edit: 13 January, 2014, 09:51:57 AM by eahm

  • C.R.Helmrich
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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
  • Last Edit: 13 January, 2014, 04:09:47 PM by C.R.Helmrich
If I don't reply to your reply, it means I agree with you.

  • eahm
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Difference between CVBR and ABR in AAC
Reply #4
Awesome, thank you Chris.