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

FFmpeg trac at avcodec.org
Sun May 4 09:47:16 CEST 2014


#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 Kamedo2):

 A Result of a quick analysis, using 17 music tracks:


 '''Default ABR''' 128kbps
 Min / '''Average''' / Max bitrate: 129 / '''130''' / 131 kbps
 Average Speed: '''12.9'''x
 ffmpeg_r62950_v8f -i %i -c:a aac -strict experimental -b:a 128k %o
 This sounds great for 128 kbps.

 '''Default VBR''' q1
 Min / '''Average''' / Max bitrate: 169 / '''192''' / 211 kbps
 Average Speed: '''14.1'''x
 ffmpeg_r62950_v8f -i %i -c:a aac -strict experimental -q:a 1 %o
 Sounds very clear, but not something expected from 192 kbps.

 '''ABR -cutoff 22000'''
 Min / '''Average''' / Max bitrate: 3 / '''4''' / 4 kbps
 Average Speed: '''14.1'''x
 ffmpeg_r62950_v8f -i %i -c:a aac -strict experimental -b:a 64 -cutoff
 22000 %o
 The sound is almost silent. The value very close to nyquist freq seems to
 cripple the LPF.

 '''ABR with ms_off'''
 Min / '''Average''' / Max bitrate: 128 / '''129''' / 131 kbps
 Average Speed: '''14.1'''x
 ffmpeg_r62950_v8f -i %i -c:a aac -strict experimental -b:a 128k -aac_coder
 anmr %o
 Sounds bad when transients exist.

 '''ABR with -aac_coder fast'''
 Min / '''Average''' / Max bitrate: 128 / '''134''' / 141 kbps
 Average Speed: '''28.0'''x
 ffmpeg_r62950_v8f -i %i -c:a aac -strict experimental -b:a 128k -aac_coder
 fast %o
 This is fast, but with very bad quality. I don't know if there's good use
 of this option.

 '''ABR with -aac_coder anmr'''
 Min / '''Average''' / Max bitrate: 130 / '''134''' / 141 kbps
 Average Speed: '''8.0'''x
 ffmpeg_r62950_v8f -i %i -c:a aac -strict experimental -b:a 128k -aac_coder
 anmr %o
 Sounds bad when transients exist. Noticably worse than the default ABR,
 and it's slow.

 '''VBR with -aac_coder anmr'''
 Min / '''Average''' / Max bitrate: 172 / '''191''' / 213 kbps
 Average Speed: '''7.5'''x
 ffmpeg_r62950_v8f -i %i -c:a aac -strict experimental -q:a 1 -aac_coder
 anmr %o
 Sounds slightly bad when transients exist. It's slow.

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Ticket URL: <https://trac.ffmpeg.org/ticket/2686#comment:281>
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