[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
-------------------------------------+-------------------------------------
             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 changed aaccoder.c line 806 from
 {{{
                 ? (refbits * 1.6f * avctx->sample_rate / 1024)
 }}}
 to
 {{{
                 ? (refbits * 2.4f * avctx->sample_rate / 1024)
 }}}
 This is certainly better, although exact optimal value is debatable.


 I encoded 2 days of diverse sounds with many settings, and listened to 2
 hours of the sounds. This encoder do a relatively good job even in abr
 96kbps. It's not a blind test, but I feel the improvement. Also, I
 compared abr 128kbps vs vbr -q 0.3, but still, abr is better. The vbr
 exposes its weak point in relatively quiet, tonal sections. Low S/N and
 stronger LPF effect.

 [[Image(http://i40.tinypic.com/r1l7j4.png)]]

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Ticket URL: <https://ffmpeg.org/trac/ffmpeg/ticket/2686#comment:160>
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