1. 11 Oct, 2015 1 commit
    • Claudio Freire's avatar
      AAC encoder: Extensive improvements · 01ecb717
      Claudio Freire authored
      This finalizes merging of the work in the patches in ticket #2686.
      
      Improvements to twoloop and RC logic are extensive.
      
      The non-exhaustive list of twoloop improvments includes:
       - Tweaks to distortion limits on the RD optimization phase of twoloop
       - Deeper search in twoloop
       - PNS information marking to let twoloop decide when to use it
         (turned out having the decision made separately wasn't working)
       - Tonal band detection and priorization
       - Better band energy conservation rules
       - Strict hole avoidance
      
      For rate control:
       - Use psymodel's bit allocation to allow proper use of the bit
         reservoir. Don't work against the bit reservoir by moving lambda
         in the opposite direction when psymodel decides to allocate more/less
         bits to a frame.
       - Retry the encode if the effective rate lies outside a reasonable
         margin of psymodel's allocation or the selected ABR.
       - Log average lambda at the end. Useful info for everyone, but especially
         for tuning of the various encoder constants that relate to lambda
         feedback.
      
      Psy:
       - Do not apply lowpass with a FIR filter, instead just let the coder
         zero bands above the cutoff. The FIR filter induces group delay,
         and while zeroing bands causes ripple, it's lost in the quantization
         noise.
       - Experimental VBR bit allocation code
       - Tweak automatic lowpass filter threshold to maximize audio bandwidth
         at all bitrates while still providing acceptable, stable quality.
      
      I/S:
       - Phase decision fixes. Unrelated to #2686, but the bugs only surfaced
         when the merge was finalized. Measure I/S band energy accounting for
         phase, and prevent I/S and M/S from being applied both.
      
      PNS:
       - Avoid marking short bands with PNS when they're part of a window
         group in which there's a large variation of energy from one window
         to the next. PNS can't preserve those and the effect is extremely
         noticeable.
      
      M/S:
       - Implement BMLD protection similar to the specified in
         ISO-IEC/13818:7-2003, Appendix C Section 6.1. Since M/S decision
         doesn't conform to section 6.1, a different method had to be
         implemented, but should provide equivalent protection.
       - Move the decision logic closer to the method specified in
         ISO-IEC/13818:7-2003, Appendix C Section 6.1. Specifically,
         make sure M/S needs less bits than dual stereo.
       - Don't apply M/S in bands that are using I/S
      
      Now, this of course needed adjustments in the compare targets and
      fuzz factors of the AAC encoder's fate tests, but if wondering why
      the targets go up (more distortion), consider the previous coder
      was using too many bits on LF content (far more than required by
      psy), and thus those signals will now be more distorted, not less.
      
      The extra distortion isn't audible though, I carried extensive
      ABX testing to make sure.
      
      A very similar patch was also extensively tested by Kamendo2 in
      the context of #2686.
      01ecb717
  2. 05 Sep, 2015 1 commit
    • Rostislav Pehlivanov's avatar
      aacenc_is: add a flag to use pure coefficients instead · 4565611b
      Rostislav Pehlivanov authored
      This commit adds a flag to use the pure coefficients instead
      of the processed ones (sce->coeffs). This is needed because
      IS will apply the changes to the coefficients immediately
      before the adjust_common_prediction function and it doesn't
      make sense to measure stereo channel coefficient difference
      when one of the channels coefficients are all zero.
      
      Therefore add a flag to use pure coefficients in that case.
      TNS is the only thing touching the coefficients before IS
      so common window prediction will not take that into account
      but the effect of the TNS filter per coefficient can be small
      (a few percent) so to some approximation it's fine to just
      ignore that.
      
      Also fixed a small error which doesn't alter the results
      that much. pow(sqrt(number), 3.0/4.0) == pow(number, 3.0/8.0) !=
      pow(number, 3.0/4.0).
      Signed-off-by: 's avatarRostislav Pehlivanov <atomnuker@gmail.com>
      4565611b
  3. 22 Aug, 2015 4 commits
  4. 21 Aug, 2015 1 commit
    • Rostislav Pehlivanov's avatar
      aaccoder: move the Intensity Stereo implementation out · d1ca7142
      Rostislav Pehlivanov authored
      This commit moves the intensity stereo implementation
      out from aaccoder and into a separate file. This was
      possible using the previous commits.
      
      This commit also drastically improves the IS implementation
      by making it phase invariant e.g. it will always choose the
      best possible phase regardless of whether M/S coding is on
      or most of the coefficients have identical phases.
      This also increases the quality and reduces any distortions
      introduced by enablind intensity stereo.
      
      Users are encouraged to test it out using the -aac_is 1
      parameter as it has always been.
      Signed-off-by: 's avatarRostislav Pehlivanov <atomnuker@gmail.com>
      d1ca7142