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• Using gcovr with FFmpeg

  6 septembre 2010, par Multimedia Mike — FATE Server

  When I started investigating code coverage tools to analyze FFmpeg, I knew there had to be an easier way to do what I was trying to do (obtain code coverage statistics on a macro level for the entire project). I was hoping there was a way to ask the GNU gcov tool to do this directly. John K informed me in the comments of a tool called gcovr. Like my tool from the previous post, gcovr is a Python script that aggregates data collected by gcov. gcovr proves to be a little more competent than my tool.

  Results
  Here is the spreadsheet of results, reflecting FATE code coverage as of this writing. All FFmpeg source files are on the same sheet this time, including header files, sorted by percent covered (ascending), then total lines (descending).

  Methodology
  I wasn’t easily able to work with the default output from the gcovr tool. So I modified it into a tool called gcovr-csv which creates data that spreadsheets can digest more easily.

  • Build FFmpeg using the '-fprofile-arcs -ftest-coverage' in both the extra cflags and extra ldflags configuration options
  • 'make'
  • 'make fate'
  • From build directory : 'gcovr-csv > output.csv'
  • Massage the data a bit, deleting information about system header files (assuming you don’t care how much of /usr/include/stdlib.h is covered — 66%, BTW)

  Leftovers
  I became aware of some spreadsheet limitations thanks to this tool :

  1. OpenOffice can’t process percent values correctly– it imports the percent data from the CSV file but sorts it alphabetically rather than numerically.
  2. Google Spreadsheet expects CSV to really be comma-delimited– forget about any other delimiters. Also, line length is an issue which is why I needed my tool to omit the uncovered ine number ranges, which it does in its default state.

• Writing x264 from OpenCV 3 with FFmpeg on Linux

  7 septembre 2018, par Greg Kramida

  I’m having trouble writing h264 video with OpenCV 3 via FFmpeg ("’X’,’2’,’6’,’4’" FOURCC). I’ve seen all the related posts so far on SO, but nothing helps. Code :

  cv::VideoWriter writer(output_path.string(),    CV_FOURCC('X','2','6','4'), 60, frame_size);

  Output :

  OpenCV : FFMPEG : tag 0x34363258/’X264’ is not supported with codec id
  28 and format ’mp4 / MP4 (MPEG-4 Part 14)’ OpenCV : FFMPEG : fallback to
  use tag 0x00000021/’ !???’

  The resulting video is extremely small (byte-wise) and unreadable. Setting the four_cc to -1 results in "unknown tag" from FFmpeg, I don’t get any prompt to choose codec as others suggested.

  The OpenCV 3 doc states :

  FFMPEG backend with MP4 container natively uses other values as fourcc
  code : see ObjectType, so you may receive a warning message from OpenCV
  about fourcc code conversion.

  That page they refrence doesn’t have h264 / x264 listed, and I’m not sure how to interpret that statement, since earlier SO posts seem to all list X.2.6.4 as the appropriate code. Using H.2.6.4 actually gives identical output.

  Any suggestions / workarounds ?

  P.S. the ffmpeg is most up-to-date from Ubuntu maintainers, it lists that it was configured with --enable-libx264

  EDIT : I tried to use the mkv container instead of mp4. The warning about tag not being supported went away, but the resulting video is still unreadable.

• Writing x264 from OpenCV 3 with FFmpeg on Linux

  19 février 2016, par Greg Kramida

  I’m having trouble writing h264 video with OpenCV 3 via FFmpeg ("’X’,’2’,’6’,’4’" FOURCC). I’ve seen all the related posts so far on SO, but nothing helps. Code :

  cv::VideoWriter writer(output_path.string(),    CV_FOURCC('X','2','6','4'), 60, frame_size);

  Output :

  OpenCV : FFMPEG : tag 0x34363258/’X264’ is not supported with codec id
  28 and format ’mp4 / MP4 (MPEG-4 Part 14)’ OpenCV : FFMPEG : fallback to
  use tag 0x00000021/’ !???’

  The resulting video is extremely small (byte-wise) and unreadable. Setting the four_cc to -1 results in "unknown tag" from FFmpeg, I don’t get any prompt to choose codec as others suggested.

  The OpenCV 3 doc states :

  FFMPEG backend with MP4 container natively uses other values as fourcc
  code : see ObjectType, so you may receive a warning message from OpenCV
  about fourcc code conversion.

  That page they refrence doesn’t have h264 / x264 listed, and I’m not sure how to interpret that statement, since earlier SO posts seem to all list X.2.6.4 as the appropriate code. Using H.2.6.4 actually gives identical output.

  Any suggestions / workarounds ?

  P.S. the ffmpeg is most up-to-date from Ubuntu maintainers, it lists that it was configured with --enable-libx264

  EDIT : I tried to use the mkv container instead of mp4. The warning about tag not being supported went away, but the resulting video is still unreadable.