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• avformat/avformat : Update av_read_frame() documentation

  1er décembre 2019, par Andreas Rheinhardt

  avformat/avformat : Update av_read_frame() documentation
  This commit updates the documentation of av_read_frame() to match its
  
  actual behaviour in several ways :
  1. On success, av_read_frame() always returns refcounted packets.
  
  2. It can handle uninitialized packets.
  
  3. On error, it always returns blank packets.
  This will allow callers to not initialize or unref unnecessarily.
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
  

  • [DH] doc/APIchanges
  • [DH] libavformat/avformat.h

• Why use sysconf(_SC_NPROCESSORS_CONF) to get the number of CPU cores in x264 ?

  5 novembre 2017, par bknieven

  I find x264 use sysconf(_SC_NPROCESSORS_CONF) instead of sysconf(SC_NPROCESSORS_ONLN) to get the number of CPU cores.

  Here is the code snippet in x264/common/cpu.c :

  ...
  
  #ifdef __ANDROID__
  
      // Android NDK does not expose sched_getaffinity
  
      return sysconf( _SC_NPROCESSORS_CONF );
  
  #else
  
      ...
  
  ....

  And I find the difference between _SC_NPROCESSORS_CONF and _SC_NPROCESSORS_ONLN in this manual :

  sysconf (_SC_NPROCESSORS_CONF) which returns the number of processors
  the operating system configured. But it might be possible for the
  operating system to disable individual processors and so the call
  sysconf (_SC_NPROCESSORS_ONLN) returns the number of processors which
  are currently online (i.e., available).

  I have two questions :

  1. What is the difference between "the number of processors the operating system configured" and "the number of processors which are currently online" ?
  2. Why x264 use _SC_NPROCESSORS_CONF in Android to get the number of CPU cores ?

• How to make linker ld find a file ?

  21 avril 2015, par haxan7

  I am cross compiling opencv with FFmpeg and it is throwing the following error :

  /root/work/codesourcery/arm-2013.05/bin/../lib/gcc/arm-none-linux-gnueabi/4.7.3/../../../../arm-none-linux-gnueabi/bin/ld : warning : libavcodec.so.56, needed by ../../lib/libopencv_highgui.so.2.4.10, not found (try using -rpath or -rpath-link)

  I have the libavcodec.so.56, and have put the relevant path to $PKG_CONFIG_PATH.

  doing a pkg-config —list-all | grep avcodec returns

  libavcodec                     libavcodec - FFmpeg codec library

  ls -al libs folder returns

  -rw-r--r-- 1 root root 93416352 Apr 21 06:57 libavcodec.a
  
  lrwxrwxrwx 1 root root       23 Apr 21 06:57 libavcodec.so -> libavcodec.so.56.34.100*
  
  lrwxrwxrwx 1 root root       23 Apr 21 06:57 libavcodec.so.56 -> libavcodec.so.56.34.100*
  
  -rwxr-xr-x 1 root root 10949836 Apr 21 06:57 libavcodec.so.56.34.100*

  Here are the contents of libavcodec.pc file

  prefix=/root/ARM_Install
  
  exec_prefix=${prefix}
  
  libdir=${prefix}/lib
  
  includedir=${prefix}/include
  
  
  
  Name: libavcodec
  
  Description: FFmpeg codec library
  
  Version: 56.34.100
  
  Requires: 
  
  Requires.private: libswresample >= 1.1.100, libavutil >= 54.22.101
  
  Conflicts:
  
  Libs: -L${libdir}  -lavcodec 
  
  Libs.private: -lxvidcore -lx264 -lm -pthread -ldl
  
  Cflags: -I${includedir}

  How can I make the liker find this file ?