[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 Kamedo2):

 I don't recommend to ambitiously try to save the HF content above 18kHz
 when there are enough bits. It sounds unstable. Some 1990s early MP3
 encoders had the tactic, but none of them were good. Rather, clean, fixed
 LPF should be applied at all time. Avoid the situation that one can hear
 the 12-20kHz content in some part of the music, and hearing the dull 12kHz
 LPF-like sound in the other part of the music.

 As for
 {{{
 pctx->frame_bits   = FFMIN(2560, chan_bitrate * AAC_BLOCK_SIZE_LONG /
 ctx->avctx->sample_rate);
 }}}
 do we get more stable results when the number 2560 is lowered?
 (240kbps is a 'megadose' or 'overkill' bitrate for AAC, so slight
 degradation is not a major problem.)

-- 
Ticket URL: <https://ffmpeg.org/trac/ffmpeg/ticket/2686#comment:84>
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