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• 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

• How can I prettify my compiled binary of FFmpeg ?

  2 avril 2019, par Hashim

  After many weeks and a lot of effort, I finally managed to use a Cygwin and MinGW-w64 toolchain to cross-compile a working binary of FFmpeg for Windows, complete with the superior but elusive fdk_aac encoder.

  However, comparing my newly-compiled binary with the official pre-compiled build for Windows makes me feel a little... lacking (first run is the Zeranoe build, second is my own) :

  

  Notice how the Zeranoe build’s banner is missing all of the unseemly-looking configure options apart from the external libraries. Along with that, it also has the date that the program was built on inserted right after the GCC version.

  How were the compilers of this build able to add these enhancements to their binary, and how can I do the same ? I’m assuming these are simply GCC or preprocessor options that I can’t find any information on, or maybe there’s more to it than that.

  N.B : I’m aware of the --no-banner switch for FFmpeg, and that’s not what I’m trying to do here.

• Can't decode HEVC video with DXVA2 and ffmpeg

  10 mai 2018, par Igor

  I can’t use DXVA2 hardware acceleration for decoding of HEVC video with ffmpeg. DXVA2 for H.264 works fine.

  I compiled an official example hw_decode.c from ffmpeg sources :

  https://github.com/FFmpeg/FFmpeg/blob/master/doc/examples/hw_decode.c

  When I call av_send_packet() it performs a callback assigned in AVCodecContext->get_format and returns only AV_PIX_FMT_YUV420P for HEVC video instead of AV_PIX_FMT_DXVA2_VLD for all H.264 videos. So HW decoding doesn’t work.

  Software decoding of HEVC works without problems.

  MPC-HC plays fine HEVC video with DXVA2 (CPU loading is low and Task Manager shows work of Video decoder in GPU details). My video card is Geforce 1060.