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

FFmpeg trac at avcodec.org
Fri Aug 9 07:44:36 CEST 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):

 I think I've found the source of most of the "annoying" artifacts. With
 the recent fix to psy's hole avoidance, lots of the rate control hacks in
 the lookahead code are no longer necessary, since the bit reservoir now
 actually works. Though if I do completely disable them, the target bit
 rate is largely missed, so some RC stuff is still needed.

 In short, RC hacks screw up on transients. I guess I'll have to explicitly
 limit RC hacks to non-transients (with perhaps some hysteresis). I'm
 working on a v5 fixing that.

 Still, to get to fdk quality, I think we'll need to fix M/S encoding
 (which still has some artifacts, if it didn't, it can be a big efficiency
 bost) and implement codebook 13 (which fdk seems to use, though I haven't
 confirmed this). That's a much bigger project though.

Ticket URL: <https://ffmpeg.org/trac/ffmpeg/ticket/2686#comment:138>
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