[FFmpeg-trac] #2686(avcodec:open): Native AAC encoder collapses at high bitrates on some samples

[FFmpeg]

#2686: Native AAC encoder collapses at high bitrates on some samples
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             Reporter:  Kamedo2      |                    Owner:
                 Type:  defect       |                   Status:  open
             Priority:  normal       |                Component:  avcodec
              Version:  git-master   |               Resolution:
             Keywords:  aac          |               Blocked By:
  regression                         |  Reproduced by developer:  1
             Blocking:               |
Analyzed by developer:  0            |
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Comment (by klaussfreire):

 Alright, i'm attaching a new VBR patch. CBR/ABR shouldn't have changed
 (shouldn't, but might). I will probably want to apply the same logic to
 CBR/ABR as well, since it works very well (ie: cutoff not with a filter
 but with the bit allocator, stop spending bits on HF if we're starving for
 bits).

 A heads-up: VBR's q-to-kbps curve has changed, and there's some artifacts
 that sound like scratchy noises (especially audible in the sine sample),
 that are due to clipping. I think it's not specific to this patch, but I
 just noticed it. I'm not sure how to attack it. Normally, I'd apply
 compression on the IMDCT stage, but since that's on the decoder side, I'll
 probably have to find a clever way to predict clipping on the encoder and
 compensate. Craptastic.

 Anyway, I do think VBR has been greatly improved on this patch. Let me
 know what you think.

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Ticket URL: <https://ffmpeg.org/trac/ffmpeg/ticket/2686#comment:78>
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