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• aacenc : remove ANMR coder

  8 février, par Lynne

  aacenc: remove ANMR coder
  
  If there's ever a rework of the AAC encoder, it won't start from here.
  The codec, with all its oddities and tweaks needed to acheive good quality
  has strayed far from the academic work upon which this coder was based on.
  Its been 20 years since this paper was released, and no known existing
  implementations, open-source or proprietary that we know of, are based on it.
  

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

• aacenc : remove support for AAC LTP profile

  8 février, par Lynne

  aacenc: remove support for AAC LTP profile
  
  The LTP profile of AAC is... terrible.
  It was an early 90's attempt at bridging the gap between speech
  codecs and general purpose codecs. It did so by trying to exploit the fact
  that most speech patterns are regular.
  
  Unfortunately, it went about it the same way as AAC Main, by taking
  the previous frame's samples, modifying them through an LPC filter,
  transforming them back using a forward MDCT, putting the output
  coefficients back into the current frame, and using delta coding.
  But once again, they ignored basic mathematics and MDCT leakage.
  Thankfully, because AAC LTP is meant to operate at very low bitrates,
  the extreme quantization results in most leakage being irrelevant.
  
  Unfortunately, the result is that the output sounds pretty much
  terrible regardless of whether LTP is enabled or not.
  
  This was the first attempt at trying to couple speech coding into AAC.
  No, the second attempt did not succeed either.
  Nnnneither did the third. Or fourth.
  
  For the fifth one, they literally just jammed a speech codec into AAC
  with USAC once they saw Opus do it.
  
  Just drop support for encoding AAC LTP. It was always experimental
  to begin with.
  

  • [DH] libavcodec/Makefile
  • [DH] libavcodec/aaccoder.c
  • [DH] libavcodec/aacenc.c
  • [DH] libavcodec/aacenc.h
  • [DH] libavcodec/aacenc_ltp.c
  • [DH] libavcodec/aacenc_ltp.h
  • [DH] libavcodec/aacenctab.h

• aacenc : remove support for AAC Main profile

  8 février, par Lynne

  aacenc: remove support for AAC Main profile
  
  The Main profile of AAC is... terrible.
  It enables the use of delta coding across coefficients of two frames
  to try to increase compression, and it enabled one more pole for TNS
  filters.
  
  What the AAC authors failed to take into account were basic
  mathematics, as MDCT leakage (e.g. the spread of each frequency when
  represented in a discrete spectrum) is significant in most audio codecs.
  This leads to huge variations between each frame, basically rendering
  prediction completely pointless.
  
  In fact, enabling AAC-Main prediction does not, in general, even recoup
  the metadata losses from signalling the profile and prediction properties
  in the first place. So you lose efficiency by using AAC Main.
  
  The rumor is that it was put in the AAC spec for patent reasons, though
  patent-wise, it has about as much use as a patent for a bicycle designed
  for use by snakes.
  
  The only other thing AAC Main changes is it permits 3-pole TNS filters.
  When AAC's bands are absolutely tiny, except for very high frequency bands,
  where you're likely to use PNS instead.
  
  Just get rid of it.
  

  • [DH] doc/encoders.texi
  • [DH] libavcodec/Makefile
  • [DH] libavcodec/aaccoder.c
  • [DH] libavcodec/aacenc.c
  • [DH] libavcodec/aacenc.h
  • [DH] libavcodec/aacenc_pred.c
  • [DH] libavcodec/aacenc_pred.h
  • [DH] libavcodec/aacenc_tns.c
  • [DH] libavcodec/aacenctab.h
  • [DH] tests/fate/aac.mak

• avdevice/alsa : simplify passing ff_alsa_open a channel layout

  8 février, par James Almer

  avdevice/alsa: simplify passing ff_alsa_open a channel layout
  
  This also ensures the layout set during the indev init is used instead of the
  blank one in st->codecpar.
  
  Signed-off-by: James Almer <jamrial@gmail.com>
  

  • [DH] libavdevice/alsa.c
  • [DH] libavdevice/alsa.h
  • [DH] libavdevice/alsa_dec.c
  • [DH] libavdevice/alsa_enc.c

• avformat/mov : check for tts_count before deferencing tts_data

  8 février, par James Almer

  avformat/mov: check for tts_count before deferencing tts_data
  
  Fixes ticket #11460.
  
  Signed-off-by: James Almer <jamrial@gmail.com>
  

  • [DH] libavformat/mov.c