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• 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

• opus : add a native Opus encoder

  11 février 2017, par Rostislav Pehlivanov

  opus : add a native Opus encoder
  This marks the first time anyone has written an Opus encoder without
  
  using any libopus code. The aim of the encoder is to prove how far
  
  the format can go by writing the craziest encoder for it.
  Right now the encoder’s basic, it only supports CBR encoding, however
  
  internally every single feature the CELT layer has is implemented
  
  (except the pitch pre-filter which needs to work well with the rest of
  
  whatever gets implemented). Psychoacoustic and rate control systems are
  
  under development.
  The encoder takes in frames of 120 samples and depending on the value of
  
  opus_delay the plan is to use the extra buffered frames as lookahead.
  
  Right now the encoder will pick the nearest largest legal frame size and
  
  won’t use the lookahead, but that’ll change once there’s a
  
  psychoacoustic system.
  Even though its a pretty basic encoder its already outperforming
  
  any other native encoder FFmpeg has by a huge amount.
  The PVQ search algorithm is faster and more accurate than libopus’s
  
  algorithm so the encoder’s performance is close to that of libopus
  
  at zero complexity (libopus has more SIMD).
  
  The algorithm might be ported to libopus or other codecs using PVQ in
  
  the future.
  The encoder still has a few minor bugs, like desyncs at ultra low
  
  bitrates (below 9kbps with 20ms frames).
  Signed-off-by : Rostislav Pehlivanov <atomnuker@gmail.com>
  

  • [DH] configure
  • [DH] libavcodec/Makefile
  • [DH] libavcodec/allcodecs.c
  • [DH] libavcodec/opus_celt.h
  • [DH] libavcodec/opus_pvq.c
  • [DH] libavcodec/opus_pvq.h
  • [DH] libavcodec/opusenc.c

• aacenc_tns : rework the way coefficients are calculated

  29 août 2015, par Rostislav Pehlivanov

  aacenc_tns : rework the way coefficients are calculated
  This commit abandons the way the specifications state to
  
  quantize the coefficients, makes use of the new LPC float
  
  functions and is much better.
  The original way of converting non-normalized float samples
  
  to int32_t which out LPC system expects was wrong and it was
  
  wrong to assume the coefficients that are generated are also
  
  valid. It was essentially a full garbage-in, garbage-out
  
  system and it definitely shows when looking at spectrals
  
  and listening. The high frequencies were very overattenuated.
  
  The new LPC function performs the analysis directly.
  The specifications state to quantize the coefficients into
  
  four bit index values using an asin() function which of course
  
  had to have ugly ternary operators because the function turns
  
  negative if the coefficients are negative which when encoding
  
  causes invalid bitstream to get generated.
  This deviates from this by using the direct TNS tables, which
  
  are fairly small since you only have 4 bits at most for index
  
  values. The LPC values are directly quantized against the tables
  
  and are then used to perform filtering after the requantization,
  
  which simply fetches the array values.
  The end result is that TNS works much better now and doesn’t
  
  attenuate anything but the actual signal, e.g. TNS removes
  
  quantization errors and does it’s job correctly now.
  It might be enabled by default soon since it doesn’t hurt and
  
  helps reduce nastyness at low bitrates.
  Signed-off-by : Rostislav Pehlivanov <atomnuker@gmail.com>
  

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