[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 Timothy_Gu):

 Replying to [comment:170 Kamedo2]:

 > > > Also, I think it's beneficial for the end users to set the -q:a
 value and typically gets a file with the bitrate around the set value. If
 one sets -q:a 256k, one gets a file of roughly 256kbps.
 > >
 > > That's not doable without refactoring ffmpeg. -q:a sets the
 global_quality parameter, which is specified to have a somewhat
 standardized interpretation (1.0 = 100%, what 100% means is what some
 other codec means by it, can't remember which OTOMH).
 > Is LAME breaking the convention?
 >
 https://trac.ffmpeg.org/wiki/Encoding%20VBR%20%28Variable%20Bit%20Rate%29%20mp3%20audio
 >
 >
 >
 > > However, you can get (I think) a similar result by specifying both
 -q:a and -b:a, like so:
 > >
 > > {{{
 > > ffmpeg -i somefile.flac -c:a aac -b:a 256k -q:a 1 -strict experimental
 somefile.aac
 > > }}}
 > >
 > > Although that seldom gives you 256k. The bitrate there is like a lower
 bound (aim for 256k, spend more if needed).
 > Thank you for the info. Your behavior seems much like the cvbr(most used
 mode), Apple iTunes.

 If someone is to implement cvbr, I suggest to do it like the libopus
 encoder wrapper, where users are allowed to choose a "vbr" option like
 this [http://ffmpeg.org/ffmpeg-codecs.html#Option-Mapping].

-- 
Ticket URL: <https://ffmpeg.org/trac/ffmpeg/ticket/2686#comment:173>
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