Video format
The Y4M format
Y4M is raw, uncompressed video frames used for codec testing. Y4M comes from the mjpegtools project; it stores raw frames with a short header and is the standard test format for video codecs.
When to use Y4M
Use Y4M as lossless input for encoder tests; convert it to MP4 to watch.
It is best for testing and comparing video encoders, and it opens on FFmpeg, mpv, VLC and codec research tools.
How to open it: mpv and VLC play Y4M files.
| Full name | YUV4MPEG2 |
|---|---|
| Extensions | .y4m |
| MIME type | video/x-yuv4mpeg |
| Introduced | 2001 |
| Compression | Uncompressed |
| Usually contains | uncompressed YUV frames, no audio |
| Support | Specialist format |
| Typical size | About 150 MB per second of 1080p |
Good at
- No compression, so nothing is lost
- Trivial for encoders to read
Not so good at
- Gigantic files: a minute of 1080p is several gigabytes
- No audio
The common mistake
Y4M has no compression at all, so browsers must hold a lot of data; very long clips may be too large for a phone to convert.
Questions
What is a Y4M file?
Y4M (YUV4MPEG2) is raw, uncompressed video frames used for codec testing. Y4M comes from the mjpegtools project; it stores raw frames with a short header and is the standard test format for video codecs.
How do I open a Y4M file?
mpv and VLC play Y4M files.