CONVERT
MP4 → Y4M
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Fast, secure MP4 to Y4M conversion. No registration required.
Opening note — MP4 is the MPEG-4 Part 14 container, the web's default video format with H.264/H.265 support. The Y4M you want is two clicks away. A MP4 to Y4M conversion rescues a clip that refuses to play somewhere important — a phone, a smart TV, a web uploader. KaijuConverter uses FFmpeg under the hood, the same engine video professionals rely on, and prioritises stream-copy over re-encode so the output stays faithful to the source. Background. MP4 is the MPEG-4 Part 14 container, the web's default video format with H.264/H.265 support. Destination side, Y4M is a video container, so playback depends on the codec inside as well as the wrapper itself.
MP4 Video
Source formatMP4 is the most universally supported video container format. It typically uses H.264 or H.265 video codecs with AAC audio, providing an excellent balance of quality and file size across all devices and platforms.
YUV4MPEG2
Target formatYUV4MPEG2 (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.
Why convert MP4 to Y4M
The usual reason to convert from MP4 into Y4M is the same reason anyone transcodes video: the original container is not accepted where you are trying to send the file. Swapping to Y4M flips that rejection into a clean upload without altering the footage itself.
HOW TO CONVERT
MP4 → Y4M
Provide the MP4 clip
Upload through the browser; transfers are encrypted end-to-end and files are quarantined per session.
Convert to Y4M
The conversion keeps resolution, frame rate and bit depth identical to the source unless you explicitly override them.
Save to your device
Click download to pull the Y4M to local storage; share the short-lived URL with collaborators if needed.
Common Use Cases
Share across platforms
Send Y4M files to anyone without worrying about whether they have the right software for MP4.
Embed in documents
Drop Y4M output into Word, Google Docs, PowerPoint, Notion or a website without conversion warnings.
Optimize size
Y4M often produces smaller files than MP4 for web, email and storage.
Archive & future-proof
Store in a widely-supported format that will still open on future operating systems without legacy plugins.
MP4 vs Y4M — Strengths and limitations
What each format does best, and where it falls short.
MP4 Strengths
- Universal playback — every browser, phone, TV, game console, and editing suite reads MP4.
- Supports modern codecs (H.264, H.265, AV1) with no container changes.
- Progressive streaming works with the "moov atom" at the start of the file.
- Carries subtitles, chapters, multiple audio tracks, and embedded metadata.
- ISO-standardized (ISO/IEC 14496-14) and patent-licensable via MPEG LA.
Limitations
- Codec licensing (H.264, H.265) carries royalty costs for commercial use.
- Streaming requires the moov atom at the start — a misplaced atom breaks web playback.
- Not ideal for lossless or professional editing workflows (use ProRes or DNxHD instead).
Y4M 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.
MP4 vs Y4M — Technical specifications
Side-by-side comparison of the technical details.
MP4
- MIME type
- video/mp4
- Container
- ISO Base Media File Format (ISO/IEC 14496-12)
- Common video codecs
- H.264 (AVC), H.265 (HEVC), AV1, VP9
- Common audio codecs
- AAC, MP3, FLAC, Opus
- Max file size
- Practically ~16 TB; 2^63 bytes theoretical
- Streaming
- Supported with faststart (moov atom at front)
Y4M
- MIME type
- video/x-yuv4mpeg2
- Extension
- .y4m
- Pixel format
- YUV 4:2:0, 4:2:2, 4:4:4
- Header
- ASCII single line
| Specification | MP4 | Y4M |
|---|---|---|
| MIME type | video/mp4 | video/x-yuv4mpeg2 |
| Container | ISO Base Media File Format (ISO/IEC 14496-12) | — |
| Common video codecs | H.264 (AVC), H.265 (HEVC), AV1, VP9 | — |
| Common audio codecs | AAC, MP3, FLAC, Opus | — |
| Max file size | Practically ~16 TB; 2^63 bytes theoretical | — |
| Streaming | Supported with faststart (moov atom at front) | — |
| Extension | — | .y4m |
| Pixel format | — | YUV 4:2:0, 4:2:2, 4:4:4 |
| Header | — | ASCII single line |
MP4 vs Y4M — Typical file sizes
Approximate file sizes for common scenarios.
MP4
- Smartphone video (1080p, 1 min) 60–120 MB
- 4K video (1 min, H.265) 200–400 MB
- Streamed movie (90 min, H.264) 1–4 GB
- Social clip (15s, H.264, 720p) 3–8 MB
Y4M
- 10 sec 1080p Y4M ~600 MB
- 1 min 4K Y4M ~14 GB
Quality & Compatibility
The conversion does not upscale or sharpen the video. A 1080p MP4 produces a 1080p Y4M; a 4K source stays 4K unless you select a lower output resolution explicitly. Picking higher bitrates does not improve perceived quality beyond the source ceiling.
Tips for Best Results
- If your MP4 has variable frame rate, force a constant frame rate in Y4M to avoid stuttering on some players and streaming platforms.
- For screen recordings at high resolution, quality 22 CRF H.264 keeps text perfectly readable at a fraction of the source size.
- Check the audio track after transcoding — some MP4 containers carry unusual audio codecs that downgrade subtly when remapped to Y4M.
Frequently Asked Questions
Only when it has to. If the codecs inside MP4 (usually H.264 or H.265 for video, AAC for audio) are accepted by Y4M, we stream-copy — the bytes are repackaged into the new container with zero re-encoding and no quality loss. When the source uses a codec the target does not support, we transcode at a matching bitrate to keep the visual quality close to the original.
With stream copy, expect the job to finish in seconds to tens of seconds regardless of video length — the work is mostly rewriting the container. Transcoding is slower (roughly real-time: a ten-minute clip takes about ten minutes) because every frame must be decoded and re-encoded. The progress bar shows which mode applies.
Yes. Resolution, frame rate, colour space and bit depth are preserved by default; stream copy is literally bit-identical on these parameters. If you explicitly pick a lower bitrate or a different codec in Advanced, the output is rebuilt to those settings, but the default is always "match the source".
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Read guideAAC: Advanced Audio Coding — The Format Behind Every MP4 and iPhone
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Read guideSecure & Private Conversion
Your files are encrypted during transfer, processed in isolated containers, and automatically deleted within 60 minutes. We never read, share, or store your data.