Recherche avancée

Sur d’autres sites (3084)

• 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 to compile github library with ndk ?

  20 octobre 2015, par Sajad Norouzi

  I want to use this library : https://github.com/guardianproject/android-ffmpeg so downloaded and copied to home/user/Download/RandD and after that I followed the instructions for compiling it with NDK but it doesn’t work well and have errors like below :

  autoreconf : ’configure.ac’ or ’configure.in’ is required

  ./configure_sox.sh : line 15 : ./configure : No such file or directory

   /Downloads/RandD/android-ffmpeg-master /Downloads/RandD/android-ffmpeg-master
   /Downloads/RandD/android-ffmpeg-master
   /Downloads/RandD/android-ffmpeg-master /Downloads/RandD/android-ffmpeg-master
   /Downloads/RandD/android-ffmpeg-master/sox /Downloads/RandD/android-ffmpeg-master /Downloads/RandD/android-ffmpeg-master
  make : * No targets specified and no makefile found. Stop.
  make : * No rule to make target `install-strip’. Stop.

  It seems that some subdirectory in this github project should get their content from other github project and for that we should use "git submodule init" and "git submodule update" but I think these two instructions doesn’t work I would be happy if you help me.

• How can I detect ffmpeg vs libav in CMake ?

  19 décembre 2015, par Scott Lamb

  My project uses libavformat to connect to rtsp:// URLs. It’s important that it set a socket timeout and reconnect on error. Unfortunately, the stimeout open option for this only exists in ffmpeg (and in particular, its libavformat versions >= 55.1.100), not the competing project libav (any version). And some systems I’d like to support (such as Raspbian Jessie) are still bundled with libav.

  So, I think my best option is to detect whether I have a suitable version using cmake, and install ffmpeg in-tree if not. I think I should be able to do this via something like :

  pkg_check_modules(FFMPEG libavutil libavcodec libavformat)
  
  
  
  if(not FFMPEG_FOUND or FFMPEG_VERSION VERSION_LESS 55.1.101)
  
    ExternalProject_Add(
  
      FfmpegProject
  
      URL "http://ffmpeg.org/releases/ffmpeg-2.8.3.tar.xz"
  
      URL_HASH "SHA1=a6f39efe1bea9a9b271c903d3c1dcb940a510c87"
  
      INSTALL_COMMAND "")
  
    ...set up flags and such to use this in-tree version...
  
  endif()

  except that I don’t know how to detect libav vs ffmpeg. I don’t see anything in the pkgconfig stuff or libavformat/version.h to distinguish them. The version numbers they use seem to overlap. It’s not obvious to me at all how to tell the difference programmatically, much less do so with a not-weird cmake rule. Any ideas ?