About Y4M Files
YUV4MPEG2
YUV4MPEG2 (Y4M) is a simple uncompressed video format that stores raw YUV pixel data with a minimal header. It is widely used as an intermediate format for video processing and quality benchmarking where no compression artifacts are acceptable.
Family
Video Files
Extension
.y4m
MIME Type
video/x-raw-yuv
Can Use As
59 34 4D 46 00 01 00 00 4B 41 49 4A
ASCII: Y4MF....KAIJ
📈 Target Minimum File Size (Guaranteed ≥ KB)
Lossless JPEG Q100 + standard COM segment padding for government & exam portals
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HOW Y4M CAME TO BE.
Y4M — YUV4MPEG2 — is a raw uncompressed video container used almost exclusively by codec developers. The format is brutally simple: a one-line ASCII header (`YUV4MPEG2 W1920 H1080 F30:1 Ip A1:1 C420 XCS=100`), then alternating frames prefixed with `FRAME\n` markers, then raw YUV pixel data. No compression, no timecodes beyond the framerate — a video codec’s perfect ground-truth input.
X264, x265, SVT-AV1, every video codec encoder on Earth accepts .y4m as test input. A 10-second 1080p Y4M weighs 600 MB uncompressed, which is the entire point: no prior codec decisions have been baked in, so codec-quality comparisons use Y4M as the source of truth.
Technical Specifications
- MIME type
- video/x-yuv4mpeg2
- Extension
- .y4m
- Pixel format
- YUV 4:2:0, 4:2:2, 4:4:4
- Header
- ASCII single line
Typical Sizes & Weights
10 sec 1080p Y4M
~600 MB
1 min 4K Y4M
~14 GB
STRENGTHS & LIMITATIONS.
Strengths
- Uncompressed raw YUV — codec benchmark truth.
- Dead-simple header.
- Universal codec development support.
Limitations
- Enormous file sizes.
- Development-only — not for consumption.
- No metadata beyond basic stream params.
CURIOSITIES & TRIVIA.
Every video codec benchmark on the planet uses Y4M as ground-truth source — x264, x265, AOM AV1, SVT-AV1.
Y4M's header is one ASCII line — trivially parseable and human-readable.
10 seconds of 1080p Y4M is about 600 MB — codec developers work with terabytes of Y4M test data.
The `FRAME\n` marker between frames is deliberately simple — parsers can seek by scanning.
Y4M's simplicity is why codec papers always cite Y4M inputs: no ambiguity about pre-processing.
Specialized Utilities for .Y4M Files
Reduce Video Size
Compress video files to reduce size for sharing and uploading. Adjustable quality settings let you balance file size and visual quality.
Convert Video for WhatsApp
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Video to GIF
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Video to MP3 Audio Extractor
Extract high-bitrate MP3 audio tracks from MP4, MOV, MKV, AVI, and WebM video recordings in seconds—ideal for podcasts, lectures, and interviews.
Extract Audio from Video
Extract the audio track from any video file and save it as MP3, WAV, or other audio formats. Perfect for creating podcasts, music rips, or voice-only recordings.
CONVERT FROM Y4M
Common Use Cases
Video quality benchmarking, uncompressed intermediate, codec testing
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Y4M vs MP4
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Popular Y4M conversions
The most-requested destinations when starting from Y4M.
Frequently Asked Questions
Y4M (YUV4MPEG2) is a video container format that bundles one or more video streams, audio tracks, and optional subtitles into a single file. The container format determines how metadata is organised and which codecs can live inside; the visual quality itself depends on the codec (H.264, H.265, VP9, AV1) rather than the Y4M wrapper. It is part of the video files family.
VLC, MPV and PotPlayer play nearly every Y4M file on desktop. Browser support varies: modern Chromium, Firefox and Safari play common containers via the HTML5 <video> tag, but niche Y4M variants may fail. If a device refuses your Y4M, convert to MP4 with our Y4M to MP4 converter for universal playback.
Upload your Y4M to KaijuConverter and pick MP4, MOV, MKV, WebM, or any other target. Our pipeline uses FFmpeg under the hood and stream-copies when codecs are compatible (no quality loss) or transcodes at high-quality defaults otherwise. Conversion runs server-side; both files delete within two hours.
Only when the target requires re-encoding. If the codecs inside Y4M match what the target container supports, FFmpeg stream-copies the streams and the output is bit-identical to the source. Transcoding uses transparent quality defaults (CRF 20–23 H.264) and produces output indistinguishable from the original at normal viewing distance.
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