# Pairwise video

Work in progress
This documentation is still a work in progress. Please bear with us as we continue to improve it.

## Encoding

We currently do not perform any transcoding of video files uploaded to our platform. For high
quality and wide browser compatibility, we recommend encoding videos using `ffmpeg` with the
following settings:


```bash
ffmpeg -i INPUT \
  -preset veryslow \
  -keyint_min 2 -g 24 -sc_threshold 0 \
  -c:v libx264 -pix_fmt yuv420p -crf 17 \
  -c:a aac -b:a 256k -ac 2 -ar 48000 \
  -movflags +frag_keyframe+empty_moov+default_base_moof \
  OUTPUT.mp4
```

A CRF value below 18 is generally considered [visually lossless](https://trac.ffmpeg.org/wiki/Encode/H.264).
Similarly for audio, compression at 256 kbps or above is considered unnoticeable [[1, 2](#references)].

#### References

[1] Pras et al. (2009). Subjective Evaluation of MP3 Compression for Different Musical Genres.
[2] Hines et al. (2014). Perceived Audio Quality for Streaming Stereo Music.