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Difference between CVBR and ABR in AAC, Split from topic 104233 (TOS #5)
eahm
post Jan 13 2014, 00:32
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QUOTE (saratoga @ Jan 12 2014, 16:07) *
Its not constrained, that would be ABR.

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

This post has been edited by eahm: Jan 13 2014, 00:32
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C.R.Helmrich
post Jan 13 2014, 09:53
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Which encoder?

Chris


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eahm
post Jan 13 2014, 15:51
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I thought there was a standard.

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

This post has been edited by eahm: Jan 13 2014, 15:51
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C.R.Helmrich
post Jan 13 2014, 22:00
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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

This post has been edited by C.R.Helmrich: Jan 13 2014, 22:09


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eahm
post Jan 13 2014, 23:23
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Awesome, thank you Chris.
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