# 视频压制技术笔记

## 不同视频网站的不同标准

* [Youtube](https://support.google.com/youtube/answer/1722171)

## Youtube

* Progressive scan (no interlacing)
  * Default: <https://blog.p2hp.com/archives/7328>
* High Profile
* 2 consecutive B frames
  * <https://www.reddit.com/r/ffmpeg/comments/g708bz/show\\_the\\_consecutive\\_bframes\\_before\\_encoding/>
  * <https://sites.google.com/site/linuxencoding/x264-ffmpeg-mapping>
* Closed GOP. GOP of half the frame rate.
  * Default: <https://streaminglearningcenter.com/blogs/open-and-closed-gops-all-you-need-to-know.html>
* CABAC
  * Default: <https://sites.google.com/site/linuxencoding/x264-ffmpeg-mapping>
* Variable bitrate. No bitrate limit required, though we offer recommended bit rates below for reference
  * Default
* Chroma subsampling: 4:2:0
  * <https://trac.ffmpeg.org/wiki/Chroma%20Subsampling>

Test commands:

```bash
ffmpeg -hwaccel_output_format qsv -hwaccel qsv -i input.mp4 -c:v h264_qsv -bf 2 -b:v 6M -maxrate 24M -global_quality 25 -look_ahead 1 -pix_fmt yuv420p output.mp4
ffmpeg -i input.mp4 -c:v libx264 -bf 2 -b:v 7M -maxrate 24M -crf 30 -movflags +faststart -pix_fmt yuv420p output.mp4
# Youtube compress
ffmpeg -i input.mp4 -vf yadif,format=yuv422p -force_key_frames 'expr:gte(t,n_forced/2)' -c:v libx264 -crf ${CRF_VALUE} -maxrate 12M -bf 2 -c:a aac -ac 2 -ar 44100 -use_editlist 0 -movflags +faststart output.mp4
```

## Bilibili

## References

* <https://trac.ffmpeg.org/wiki/Encode/H.264>


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