tools/ffmpeg holds FFmpeg n9.0.2-17-g2a571b6068 (ffmpeg, ffprobe and their libraries), built by
BtbN/FFmpeg-Builds under the GPL version 3 (ffmpeg.txt). Its corresponding source is
FFmpeg at the commit it was built from, and the build scripts, which name the source
of every library linked into it at the version used:

  https://github.com/FFmpeg/FFmpeg/tree/2a571b6068
  https://github.com/BtbN/FFmpeg-Builds/tree/6c9aec5fc9a72ec3abedd1fa84db141fa18cf52b
