Y4M (raw YUV4MPEG)
Also known as: YUV4MPEG2, .y4m file, raw YUV video
Y4M (YUV4MPEG2) is an uncompressed video format that stores raw YUV frames with a simple text header. Because nothing is compressed, files are extremely large; it is used as an intermediate format for encoding and codec testing, not for everyday storage or playback.
- Uncompressed raw YUV video with a text header
- Very large files; used as an encoder input
- Transcode to MP4 or WebM for actual storage
A raw, uncompressed format
Y4M wraps a sequence of raw YUV frames — the color model most video codecs work in — with a plain-text header describing resolution, frame rate, and chroma layout. There is no compression at all, so a few seconds of Y4M can be larger than a full compressed movie.
That rawness is the point: it gives encoders a clean, lossless input, which is why it shows up in video-codec development and quality testing.
Working with Y4M
Y4M is not meant for keeping or sharing. Tools like FFmpeg and VLC read it, and the normal workflow is to feed it into an encoder and output a compressed MP4 or WebM. If you find a Y4M file eating disk space, transcoding it to a real codec recovers most of that space.