[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):

 Replying to [comment:86 klaussfreire]:
 > I just want to preserve the HF component of transients. There might be
 better ways of doing that. I guess I'll keep iterating on it. However, I
 believe the way it's being done now works well. If you check, the LP
 cutoff is chosen from the allocation given by psy. Psy contains bit
 reservoir logic, which means it will momentarily increase bits (and
 cutoff) for some difficult transients. Right now, it works wonders for hi-
 hats.

 So, if there is a group of beat sounds that is on the threshold of
 tonal/transients, the LPF is sometimes on and sometimes off? Currently,
 the on/off switch itself is audible and is quite annoying. It sounds like
 a stopwatch.

 > I will probably have to be stricter about the cutoff, though. As you
 say, when the signal by itself (not by psy's indication, but signal
 strength alone) suddenly jumps in HF content, the result is unpleasant. I
 think I have cleaned up most of those cases, but who knows. It's hard to
 discern those from actual transients.
 ffmpeg_aacvbr_pulse1.flac at -q:a 0.25 produces strange HF sounds.

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Ticket URL: <https://ffmpeg.org/trac/ffmpeg/ticket/2686#comment:87>
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