[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):

 Replying to [comment:93 Kamedo2]:
 > Is that included in a wip-v3-vbr.patch

 Yes

 > Are HF contents over cutoff*1.2 totally discarded? (I believe this is
 the best move.)

 No, and maybe that's the problem. 1.2 just happens to be the point at
 which the increased quantization floor starts zeroing out all components.
 Until that, RD optimization brings down the quantization floor to maintain
 acceptable quality, so you don't notice the floor rising (and it fact it
 doesn't for fully tonal bands, that's what RD optimization is about,
 whereas it does rise for noisy ones).

 So, in essence, up to cutoff * 1.2, tonal components are retained at the
 expense of HF noise, which seems like a sensible tradeoff.

 What must be happening, is that, on some signals, the zeroing point
 happens above 1.2, significantly above. So it's perhaps wise to hardcode
 that 1.2 value, and force a zero on those bands instead.

-- 
Ticket URL: <https://ffmpeg.org/trac/ffmpeg/ticket/2686#comment:95>
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