How to compress video size

ffmpeg -i $in -c:v libx264 -c:a libfaac -crf 20 -preset:v veryslow $out

• -crf option
  • scale: 0 – 51 (0 is lossless, 23 is the default, and 51 is worst quality possible)
  • Consider 17 or 18 to be visually lossless or nearly so; it should look the same or nearly the same as the input but it isn’t technically lossless
  • The range is exponential, so increasing the CRF value +6 results in roughly half the bitrate / file size, while -6 leads to roughly twice the bitrate.
  • via: shell - FFMPEG convert .mpg video to .mp4 without lose quality - Stack Overflow

自己试了下 0, 无损压缩, 文件大小从 30M → 300M

References

• Encode/H.264 – FFmpeg