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• FFmpeg vs Libav vs libVLC vs Gstreamer as of 2018 [on hold]

  25 avril 2018, par Dharma

  I am trying to do some video processing on real time. I was beginning to try the FFmpeg, but I saw this question :

  Why would I choose Libav over FFmpeg, or is there even a difference ?

  Which further links to this question :

  What are the differences and similarities between ffmpeg, libav, and avconv ?

  and this blog post :

  http://blog.pkh.me/p/13-the-ffmpeg-libav-situation.html

  After reading this I came to know that Libav is a fork from FFmpeg and is being developed separately. I am need of developing C++ application using either Libav or FFmpeg or libVLC or Gstreamer. I think there has been a lot of changes after these questions are answered. It would be great to have some benchmark on these tools.

  Do you guys have any preference of one over another, any benchmark results for video and audio processing ? I need to process frames fast and stream a video to multiple C++ applications, what would be the best way to solve this problem and what will be the best tool to choose ?

  So as of 2018 what is the current status of these tools on video processing.
  It would be nice to know some results from the people working on video processing who are familiar with these tools.

• error : ‘avcodec_send_packet’ was not declared in this scope

  4 juillet 2018, par StarShine

  The following snippet of ffmpeg-based code is building and working on Windows VC2012, VC20155, VC2017.

  With gcc on Ubuntu LTS 16.04 this is giving me issues, more specifically it does not seem to recognize avcodec_send_packet, avcodec_receive_frame and struct AVCodecParameters, and possibly more functions and structures that I’m not currently using.

  error : ‘AVCodecParameters’ was not declared in this scope
  error : ‘avcodec_send_packet’ was not declared in this scope
  error : ‘avcodec_receive_frame ’ was not declared in this scope

  The code snippet is :

  // the includes are actually in a precompiled header, included in cmake
  
  extern "C" {
  
  
  
  #include <libavcodec></libavcodec>avcodec.h>
  
  #include <libavdevice></libavdevice>avdevice.h>
  
  #include <libavfilter></libavfilter>avfilter.h>
  
  #include <libpostproc></libpostproc>postprocess.h>
  
  #include <libswresample></libswresample>swresample.h>
  
  #include <libswscale></libswscale>swscale.h>
  
  #include <libavformat></libavformat>avformat.h>
  
  #include <libavutil></libavutil>avutil.h>   
  
  #include <libavutil></libavutil>avassert.h>
  
  #include <libavutil></libavutil>avstring.h>
  
  #include <libavutil></libavutil>bprint.h>
  
  #include <libavutil></libavutil>display.h>
  
  #include <libavutil></libavutil>mathematics.h>  
  
  #include <libavutil></libavutil>imgutils.h>
  
  //#include <libavutil></libavutil>libm.h>
  
  #include <libavutil></libavutil>parseutils.h>
  
  #include <libavutil></libavutil>pixdesc.h>
  
  #include <libavutil></libavutil>eval.h>
  
  #include <libavutil></libavutil>dict.h>
  
  #include <libavutil></libavutil>opt.h>
  
  #include <libavutil></libavutil>cpu.h>
  
  #include <libavutil></libavutil>ffversion.h>
  
  #include <libavutil></libavutil>version.h>
  
  
  
  }
  
  
  
  //
  
  ... 
  
  {
  
      if (av_read_frame(m_FormatContext, m_Packet) &lt; 0) {
  
          av_packet_unref(m_Packet);
  
          m_AllPacketsSent = true;
  
      } else {
  
          if (m_Packet->stream_index == m_StreamIndex) {                  
  
              avcodec_send_packet(m_CodecContext, m_Packet);
  
          }
  
      }
  
  }
  
  ...

  I read up on the ffmpeg history and learned that on Debian based systems at one point they followed the fork to libavutil when that came about, and then recently some of the platforms switched back to the ffmpeg branch due to the fact that ffmpeg was much more actively supported in terms of bugfixes, features and support. As a result, some of the interfaces were possibly broken.

  I’ve seen git fixes on a library called mediatombs who seem to have ecountered the same if not very similar issues with codecpar (which I initially also had and fixed the same way) :

  https://github.com/gerbera/gerbera/issues/52

  https://github.com/gerbera/gerbera/commit/32efd463f138557c54535225d84136df95bab3dd#diff-af3b638bc2a3e6c650974192a53c7291

  Here the commit seems to fix their specific issue by wrapping the codecpar field that is being renamed back to codec, which I also applied and works.

  I wonder if anyone knows which functions can be used for the errors given above, since in fact these functions are themselves replacing deprecated functionality according the ffmpeg avcodec.h header comments. (https://www.ffmpeg.org/doxygen/trunk/avcodec_8h_source.html). I hope this does not mean I would have to settle back into avcodec_encode_video2() type of functions ?

  Update :

  For reference, it seems it has also popped up here : https://github.com/Motion-Project/motion/issues/338. The issue seems to be resolved if you can rebuild your ffmpeg stack.

  Update :

  To resolve the version API mingle, I ended up wiping out any ffmpeg reference and rebuilding ffmpeg from sources. This seems to push things further along in the right direction ; I have my source compiling correctly but there is still something wrong with the way I’m linking things together.

  Also, I’m using CMake to set up my makefiles, and using find_package for some of the dependencies and handwritten find_path / find_library stuff for everything else. I’ve seen other people complain about the following linking issue, and a ton of case-specific replies but none of them really shed some light on what the actual problem is. My installed Ubuntu version of ALSA is 1.1.xx but still I get complaints about a 0.9 version I’m supposedly linking. Anyone knows what’s wrong with this ?

  Also, my libasound.so is symbol linked into libasound.so.2.0.0 if that clears anything up. (Hope that double slashed path at the end is correct also).

  /usr/bin/ld: /usr/lib/ffmpeg/libavdevice.a(alsa.o): undefined reference to symbol 'snd_pcm_hw_params_any@@ALSA_0.9' //usr/lib/x86_64-linux-gnu/libasound.so.2: 

• avformat : add fields to AVProgram/AVStream for PMT change tracking

  18 mai 2018, par Aman Gupta

  avformat : add fields to AVProgram/AVStream for PMT change tracking
  These fields will allow the mpegts demuxer to expose details about
  
  the PMT/program which created the AVProgram and its AVStreams.
  In mpegts, a PMT which advertises streams has a version number
  
  which can be incremented at any time. When the version changes,
  
  the pids which correspond to each of it's streams can also change.
  Since ffmpeg creates a new AVStream per pid by default, an API user
  
  needs the ability to (a) detect when the PMT changed, and (b) tell
  
  which AVStream were added to replace earlier streams.
  This has been a long-standing issue with ffmpeg's handling of mpegts
  
  streams with PMT changes, and I found two related patches in the wild
  
  that attempt to solve the same problem :
  The first is in MythTV's ffmpeg fork, where they added a
  
  void (*streams_changed)(void*) ; to AVFormatContext and call it from
  
  their fork of the mpegts demuxer whenever the PMT changes.
  The second was proposed by XBMC in
  
  https://ffmpeg.org/pipermail/ffmpeg-devel/2012-December/135036.html,
  
  where they created a new AVMEDIA_TYPE_DATA stream with id=0 and
  
  attempted to send packets to it whenever the PMT changed.
  Signed-off-by : Aman Gupta <aman@tmm1.net>
  

  • [DH] doc/APIchanges
  • [DH] libavformat/avformat.h
  • [DH] libavformat/utils.c
  • [DH] libavformat/version.h