1. 18 Apr, 2015 7 commits
  2. 17 Apr, 2015 13 commits
  3. 16 Apr, 2015 15 commits
  4. 15 Apr, 2015 5 commits
    • Rostislav Pehlivanov's avatar
      aaccoder: Implement Perceptual Noise Substitution for AAC · c5d4f87e
      Rostislav Pehlivanov authored
      This commit implements the perceptual noise substitution AAC extension. This is a proof of concept
      implementation, and as such, is not enabled by default. This is the fourth revision of this patch,
      made after some problems were noted out. Any changes made since the previous revisions have been indicated.
      
      In order to extend the encoder to use an additional codebook, the array holding each codebook has been
      modified with two additional entries - 13 for the NOISE_BT codebook and 12 which has a placeholder function.
      The cost system was modified to skip the 12th entry using an array to map the input and outputs it has. It
      also does not accept using the 13th codebook for any band which is not marked as containing noise, thereby
      restricting its ability to arbitrarily choose it for bands. The use of arrays allows the system to be easily
      extended to allow for intensity stereo encoding, which uses additional codebooks.
      
      The 12th entry in the codebook function array points to a function which stops the execution of the program
      by calling an assert with an always 'false' argument. It was pointed out in an email discussion with
      Claudio Freire that having a 'NULL' entry can result in unexpected behaviour and could be used as
      a security hole. There is no danger of this function being called during encoding due to the codebook maps introduced.
      
      Another change from version 1 of the patch is the addition of an argument to the encoder, '-aac_pns' to
      enable and disable the PNS. This currently defaults to disable the PNS, as it is experimental.
      The switch will be removed in the future, when the algorithm to select noise bands has been improved.
      The current algorithm simply compares the energy to the threshold (multiplied by a constant) to determine
      noise, however the FFPsyBand structure contains other useful figures to determine which bands carry noise more accurately.
      
      Some of the sample files provided triggered an assertion when the parameter to tune the threshold was set to
      a value of '2.2'. Claudio Freire reported the problem's source could be in the range of the scalefactor
      indices for noise and advised to measure the minimal index and clip anything above the maximum allowed
      value. This has been implemented and all the files which used to trigger the asserion now encode without error.
      
      The third revision of the problem also removes unneded variabes and comparisons. All of them were
      redundant and were of little use for when the PNS implementation would be extended.
      
      The fourth revision moved the clipping of the noise scalefactors outside the second loop of the two-loop
      algorithm in order to prevent their redundant calculations. Also, freq_mult has been changed to a float
      variable due to the fact that rounding errors can prove to be a problem at low frequencies.
      Considerations were taken whether the entire expression could be evaluated inside the expression
      , but in the end it was decided that it would be for the best if just the type of the variable were
      to change. Claudio Freire reported the two problems. There is no change of functionality
      (except for low sampling frequencies) so the spectral demonstrations at the end of this commit's message were not updated.
      
      Finally, the way energy values are converted to scalefactor indices has changed since the first commit,
      as per the suggestion of Claudio Freire. This may still have some drawbacks, but unlike the first commit
      it works without having redundant offsets and outputs what the decoder expects to have, in terms of the
      ranges of the scalefactor indices.
      
      Some spectral comparisons: https://trac.ffmpeg.org/attachment/wiki/Encode/AAC/Original.png (original),
      https://trac.ffmpeg.org/attachment/wiki/Encode/AAC/PNS_NO.png (encoded without PNS),
      https://trac.ffmpeg.org/attachment/wiki/Encode/AAC/PNS1.2.png (encoded with PNS, const = 1.2),
      https://trac.ffmpeg.org/attachment/wiki/Encode/AAC/Difference1.png (spectral difference).
      The constant is the value which multiplies the threshold when it gets compared to the energy, larger
      values means more noise will be substituded by PNS values. Example when const = 2.2:
      https://trac.ffmpeg.org/attachment/wiki/Encode/AAC/PNS_2.2.pngReviewed-by: 's avatarClaudio Freire <klaussfreire@gmail.com>
      Signed-off-by: 's avatarMichael Niedermayer <michaelni@gmx.at>
      c5d4f87e
    • Nedeljko Babic's avatar
      libavutil/softfloat: Change order of fields in SoftFloat structure. · f4ccf389
      Nedeljko Babic authored
      Softfloat will be used in implementation of AAC fixed point decoder.
      This change is needed in order to more easily integrate ffmpegs softfloat in
      already developed algorithm for AAC.
      Signed-off-by: 's avatarNedeljko Babic <nedeljko.babic@imgtec.com>
      Signed-off-by: 's avatarMichael Niedermayer <michaelni@gmx.at>
      f4ccf389
    • Michael Niedermayer's avatar
      574978d2
    • Diego Biurrun's avatar
      configure: Simplify avisynth check · 1336bb06
      Diego Biurrun authored
      1336bb06
    • Diego Biurrun's avatar
      247aa7af