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

FFmpeg trac at avcodec.org
Tue Dec 10 07:04:19 CET 2013

#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            |

Comment (by klaussfreire):

 Sadly, no. I thought so, but further tests (at various bitrates) show
 saturation. Not the same issue as the original in the OP, but an issue

 I have only attacked M/S coding and some bit allocation inefficiencies,
 but the improvement seemed to improve those issues during initial tests
 since tonal band encoding improved significantly, but it's still not
 enough it seems to avoid clipping due to quantization noise.

 Since the original signal is saturated already, I may have a relatively
 easy fix for it: all quantization noise risks the same artifacts, but I
 believe there is only one fix, which involves tweaking rounding of strong

 That needs careful calibration, however, in order to avoid modifying
 behavior on non-clipping signals (since rounding towards zero generally
 induces higher SNR), but I'll be travelling soon and won't be able to work
 much on it till jan 1st.

Ticket URL: <https://trac.ffmpeg.org/ticket/2686#comment:237>
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