[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       |  klaussfreire
             Priority:  normal       |                   Status:  open
              Version:  git-master   |                Component:  avcodec
             Keywords:  aac          |               Resolution:
  regression                         |               Blocked By:
             Blocking:               |  Reproduced by developer:  1
Analyzed by developer:  0            |
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Comment (by klaussfreire):

 Well, time for an update...

 I did some tests, and faad's problem is with correlated PNS bands (PNS +
 ms_mask). It seems to be applying the M/S transform even though the specs
 clearly state that when PNS is used in conjunction with ms_mask bits, it
 should not.

 I'd consider that a faad bug, but we are indeed producing "weird"
 bitstreams (we signal correlated PNS when only one side uses PNS, which
 makes the ms_mask unnecessary). Avoiding that weirdness works around
 faad's bug (and avoids possibly triggering similar bugs in other
 decoders).

 I'm working on that patch now (thoroughly testing now).

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Ticket URL: <https://trac.ffmpeg.org/ticket/2686#comment:473>
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