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• aaccoder : remove previous PNS implementation from twoloop

  2 juillet 2015, par Rostislav Pehlivanov

  aaccoder : remove previous PNS implementation from twoloop
  This commit undoes commit c5d4f87e81111427c0952278ec247fa8ab1e6e52
  
  and removes PNS band marking from the twoloop coder, which has
  
  been reimplemented in a better way in this series of patches.
  Reviewed-by : Claudio Freire <klaussfreire@gmail.com>
  
  Signed-off-by : Michael Niedermayer <michaelni@gmx.at>
  

  • [DH] libavcodec/aaccoder.c

• aaccoder : add a new perceptual noise substitution implementation

  2 juillet 2015, par Rostislav Pehlivanov

  aaccoder : add a new perceptual noise substitution implementation
  This commit finalizes the PNS implementation previously added to the encoder
  
  by moving it to a seperate function search_for_pns() and thus making it
  
  coder-generic. This new implementation makes use of the spread field of
  
  the psy bands and the lambda quality feedback paremeter. The spread of the
  
  spectrum in a band prevents PNS from being used excessively and thus preserve
  
  more phase information in high frequencies.  The lambda parameter allows
  
  the number of PNS-marked bands to vary based on the lambda parameter and the
  
  amount of bits available, making better choices on which bands are to be marked
  
  as noise. Comparisons with the previous PNS implementation can be found
  
  here : https://trac.ffmpeg.org/attachment/wiki/Encode/AAC/
  This is V2 of the patch, the changes from the previous version being that this
  
  version uses the new band->spread metric from aacpsy and normalizes the
  
  energy using the group size. These changes were suggested by Claudio Freire
  
  on the mailing list. Another change is the use of lambda to alter the
  
  frequency threshold. This change makes the actual threshold frequencies
  
  vary between +-2Khz of what’s specified, depending on frame encoding performance.
  Reviewed-by : Claudio Freire <klaussfreire@gmail.com>
  
  Signed-off-by : Michael Niedermayer <michaelni@gmx.at>
  

  • [DH] libavcodec/aaccoder.c
  • [DH] libavcodec/aacenc.c
  • [DH] libavcodec/aacenc.h

• aacenc : implement Intensity Stereo encoding support

  2 juillet 2015, par Rostislav Pehlivanov

  aacenc : implement Intensity Stereo encoding support
  This commit implements intensity stereo coding support
  
  to the native aac encoder. This is a way to increase the efficiency
  
  of the encoder by zeroing the right channel’s spectral coefficients
  
  (in a channel pair) and rederiving them in the decoder using information
  
  from the scalefactor indices of special band types. This commit
  
  confomrs to the official ISO 13818-7 specifications, although due to
  
  their ambiguity certain deviations have been taken to ensure maximum
  
  sound quality. This commit has been extensively tested and has shown
  
  to not result in audiable audio artifacts unless in extreme cases.
  
  This commit also adds an option, aac_is, which has the value of
  
  0 by default. Intensity Stereo is part of the scalable aac profile
  
  and is thus non-default.
  The way IS coding works is that it rederives the right channel’s
  
  spectral coefficients from the left channel via the scalefactor
  
  index values left in the right channel. Since an entire band’s
  
  spectral coefficients do not need to be coded, the encoder’s
  
  efficiency jumps up and it unzeroes some high frequency values
  
  which it previously did not have enough bits to encode. That way
  
  less information is lost than the information lost by rederiving
  
  the spectral coefficients with some error. This is why the
  
  filesize of files encoded with IS do not decrease significantly.
  
  Users wishing that IS coding should reduce filesize are expected
  
  to reduce their encoding bitrates appropriately.
  This is V2 of the commit. The old version did not mark ms_mask as
  
  0 since M/S and IS coding are incompactible, which resulted in
  
  distortions with M/S coding enabled. This version also improves
  
  phase detection by measuring it for every spectral coefficient in
  
  the band and using a simple majority rule to determine whether the
  
  coefficients are in or out of phase. Also, the energy values per
  
  spectral coefficient were changed as to reflect the
  
  official specifications.
  Reviewed-by : Claudio Freire <klaussfreire@gmail.com>
  
  Signed-off-by : Michael Niedermayer <michaelni@gmx.at>
  

  • [DH] libavcodec/aaccoder.c
  • [DH] libavcodec/aacenc.c
  • [DH] libavcodec/aacenc.h