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

FFmpeg trac at avcodec.org
Sun Jul 14 22:13:54 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 Kamedo2):

 Isn't line 334 of libavcodec/aacpsy.c:
 {{{
         for (g = 0; g < ctx->num_bands[j]-1; g++) {
             AacPsyCoeffs *coeff = &coeffs[g];
             float bark_width = coeffs[g+1].barks - coeffs->barks;
             coeff->spread_low[0] = pow(10.0, -bark_width *
 PSY_3GPP_THR_SPREAD_LOW);
             coeff->spread_hi [0] = pow(10.0, -bark_width *
 PSY_3GPP_THR_SPREAD_HI);
             coeff->spread_low[1] = pow(10.0, -bark_width * en_spread_low);
             coeff->spread_hi [1] = pow(10.0, -bark_width * en_spread_hi);
             pe_min = bark_pe * bark_width;
             minsnr = exp2(pe_min / band_sizes[g]) - 1.5f;
             coeff->min_snr = av_clipf(1.0f / minsnr, PSY_SNR_25DB,
 PSY_SNR_1DB);
         }
 }}}
 strange? I doubt the sanity of lower spreading function at the highest
 band, because using -cutoff 18000 option improves the quality on
 problematic samples, and these problematic samples always includes strong
 20-22kHz sounds. (The default cutoff is 18k at 192kbps, 20k at 256kbps,
 and 22k at 320kbps.)

-- 
Ticket URL: <https://ffmpeg.org/trac/ffmpeg/ticket/2686#comment:31>
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