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• Anomalie #4052 : Visualiser ses messages dans le privé

  28 novembre 2017, par tcharlss (*´_ゝ｀)

  J’ai bien ce lien sur contrib, spip.net et forum. C’est tout en bas de la boîte d’infos :

  AUTEUR NUMÉRO
  6944
  Je suis rédacteur
  
  4 articles
  
  24 messages de forum
  
  Voir en ligne
  

• 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

• lavc : implement an ATRAC9 decoder

  30 juin 2018, par Rostislav Pehlivanov

  lavc : implement an ATRAC9 decoder
  This commit implements a full ATRAC9 decoder, a simple low-delay codec
  
  developed by Sony and used in most PSVita games, some PS3 games and some
  
  PS4 games. Its similar to AAC in that it uses Huffman coded scalefactors
  
  but instead of vector quantization it just Huffman codes the spectral
  
  coefficients (in a way similar to how Opus splits band energy coding
  
  into coarse and fine precision). It opts to write rather large Huffman
  
  codes by packing several small coefficients into one Huffman coded
  
  symbol, though I don't believe this increases efficiency at all.
  
  Band extension implements SBC in a simple way, first it mirrors the
  
  lower spectrum onto the higher frequencies and then it uses one of 5
  
  filters to shape it. Noise substitution is implemented via 2 of them.
  
  Unlike previous ATRAC codecs, there's no QMF, this is a standard MDCT
  
  codec.
  Based off of the reverse engineering work of Alex Barney.
  Signed-off-by : Rostislav Pehlivanov <atomnuker@gmail.com>
  

  • [DH] Changelog
  • [DH] configure
  • [DH] libavcodec/Makefile
  • [DH] libavcodec/allcodecs.c
  • [DH] libavcodec/atrac9dec.c
  • [DH] libavcodec/atrac9tab.h
  • [DH] libavcodec/avcodec.h
  • [DH] libavcodec/codec_desc.c
  • [DH] libavcodec/utils.c
  • [DH] libavcodec/version.h