FFmpeg is an open source command-line tool for manipulating audio and video files: converting formats, compressing, trimming, assembling, adding subtitles or streaming.

Converting social networks

ffmpeg -i INPUT.ext \
  -c:v libx264 \
  -profile:v main \
  -level 4.0 \
  -pix_fmt yuv420p \
  -movflags +faststart \
  -c:a aac \
  -b:a 128k \
  OUTPUT.mp4

Sources