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• Where to inject code to print out motion vectors and DC coefficients inside ffmpeg lib

  12 juin 2018, par Kindermann

  For research purposes, I need to extract information about motion vectors and DC coefficients from an MPEG4 video.

  I have inserted many printf into virtually each function inside mpeg4videodec.c and recompiled the ffmpeg library then executed demuxing_decoding.c which is available at : http://ffmpeg.org/doxygen/trunk/demuxing_decoding_8c-example.html

  Surprisingly none of those printf I inserted was shown in the console. Can you give me some hints which file(s) in the ffmpeg library should I touch in order to print out MVectors and DC coefficients of a MPEG4 video file ?

• Where to inject code to print out motion vectors and DC coefficients inside ffmpeg lib

  6 mai 2016, par Kindermann

  For research purposes, I need to extract information about motion vectors and DC coefficients from an MPEG4 video.

  I have inserted many printf into virtually each function inside mpeg4videodec.c and recompiled the ffmpeg library then executed demuxing_decoding.c which is available at : http://ffmpeg.org/doxygen/trunk/demuxing_decoding_8c-example.html

  Surprisingly none of those printf I inserted was shown in the console. Can you give me some hints which file(s) in the ffmpeg library should I touch in order to print out MVectors and DC coefficients of a MPEG4 video file ?

• ffmpeg unexpected exit code 1 for -list_devices and -list_options

  8 janvier 2024, par djvg

  Description

  


  If I run any of the following commands from the examples in the documentation, using ffmpeg 4.2.2 on Windows 10, the requested information is successfully displayed in the console, but the process exits with exit code 1, instead of the expected 0 (success).

  


  ffmpeg -list_devices true -f dshow -i dummy

ffmpeg -list_options true -f dshow -i video="MyCamera"


  


  As far as I know, exit code 1 on Windows implies "Incorrect function", so I consider this behavior to be unexpected.

  


  If I stream camera input to disk, using e.g. ffmpeg -f dshow -i video="MyCamera" "myfile.mp4", then stop using q, the exit code is 0, as expected.

  


  Question

  


  Does the exit code 1 constitute normal behavior for ffmpeg, or am I doing something wrong ?

  


  Relevance

  


  When running the commands manually, from the command line, the exit code does not make much difference, as long as the requested information is displayed.

  


  However, when running the commands programmatically, it may cause trouble. For example, using Python's subprocess.run(..., check=True), the nonzero exit code causes a CalledProcessError.

  


  Of course there are ways around this, e.g. use check=False, but the point is that a workaround would not be necessary if ffmpeg behaved as expected, i.e. returned 0.