#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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