CONVERT
Y4M → MJPEG
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Fast, secure Y4M to MJPEG conversion. No registration required.
Here is the short version — Y4M is a video container, so playback depends on the codec inside as well as the wrapper itself. Hence the need for MJPEG. A Y4M to MJPEG conversion makes a recording portable. Video containers matter more than you might expect: players that handle MJPEG natively sometimes stutter or flat-out reject Y4M with the same codec inside. Uploading above triggers a stream-level rewrap when possible, keeping the visible quality identical to the source. Worth knowing: Y4M is a video container, so playback depends on the codec inside as well as the wrapper itself. Meanwhile MJPEG is a video container, so playback depends on the codec inside as well as the wrapper itself.
YUV4MPEG2
Source 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.
Motion JPEG
Target formatMotion JPEG (MJPEG) is a video format where each frame is independently compressed as a JPEG image. This intraframe-only approach enables easy frame-accurate editing and is widely used in security cameras and digital camera video modes.
Why convert Y4M to MJPEG
Sending Y4M to someone on a non-matching operating system frequently leads to "file cannot be opened". MJPEG avoids that by sitting in the middle of everyone's compatibility list. The repackage runs quickly and without generational loss when codecs already align.
HOW TO CONVERT
Y4M → MJPEG
Drop the video file
Select a Y4M file. We read the container and stream descriptors to plan the conversion.
FFmpeg handles the repackage
When codecs align, FFmpeg rewraps the existing streams into a MJPEG container — no quality loss, near-instant finish.
Retrieve the MJPEG
The MJPEG download is ready in seconds for stream-copy jobs, minutes for full transcodes.
Common Use Cases
Share across platforms
Send MJPEG files to anyone without worrying about whether they have the right software for Y4M.
Embed in documents
Drop MJPEG output into Word, Google Docs, PowerPoint, Notion or a website without conversion warnings.
Optimize size
MJPEG often produces smaller files than Y4M 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.
Y4M vs MJPEG — Strengths and limitations
What each format does best, and where it falls short.
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.
MJPEG Strengths
- Trivially simple — any JPEG decoder handles frames.
- Every frame is a keyframe — instant seek and edit.
- No inter-frame dependencies — recover from packet loss easily.
- Hardware cost is minimal — any JPEG decoder works.
- Lossless across edits — cutting and rejoining doesn't degrade quality.
Limitations
- 3-5× larger than MPEG-2; 8-10× larger than H.264 at comparable quality.
- No audio — requires a separate track.
- No standard container — appears inside AVI, MOV, MKV, MJPEG-over-HTTP.
Y4M vs MJPEG — Technical specifications
Side-by-side comparison of the technical details.
Y4M
- MIME type
- video/x-yuv4mpeg2
- Extension
- .y4m
- Pixel format
- YUV 4:2:0, 4:2:2, 4:4:4
- Header
- ASCII single line
MJPEG
- MIME type
- video/x-motion-jpeg
- Extension
- .mjpeg, .mjpg
- Frame format
- Sequential JPEG (Baseline, usually 4:2:0)
- Typical containers
- AVI, MOV, MP4 (rare), raw stream
- Common in
- IP security cameras, USB webcams, scientific imaging
| Specification | Y4M | MJPEG |
|---|---|---|
| MIME type | video/x-yuv4mpeg2 | video/x-motion-jpeg |
| Extension | .y4m | .mjpeg, .mjpg |
| Pixel format | YUV 4:2:0, 4:2:2, 4:4:4 | — |
| Header | ASCII single line | — |
| Frame format | — | Sequential JPEG (Baseline, usually 4:2:0) |
| Typical containers | — | AVI, MOV, MP4 (rare), raw stream |
| Common in | — | IP security cameras, USB webcams, scientific imaging |
Y4M vs MJPEG — Typical file sizes
Approximate file sizes for common scenarios.
Y4M
- 10 sec 1080p Y4M ~600 MB
- 1 min 4K Y4M ~14 GB
MJPEG
- 1-min VGA webcam clip 40-80 MB
- 1-min 1080p IP camera stream 300-500 MB
- Canon DSLR 720p video (1 min) ~550 MB
Quality & Compatibility
Resolution, frame rate and colour space are preserved end-to-end. If the MJPEG container does not support some Y4M features (chapters, multiple subtitle tracks, DRM-protected streams), those are flattened or dropped with a warning. Hard-coded subtitles in the video frames always survive.
Tips for Best Results
- Embedded subtitle tracks convert between Y4M and MJPEG when both containers support the same subtitle codec; otherwise burn the subtitles into the video first.
- For portrait (9:16) clips, make sure the MJPEG encoder preserves the correct display aspect ratio — some players default to 16:9 if SAR is ambiguous.
- Long recordings (over an hour) benefit from chapter metadata; MJPEG may not preserve Y4M chapters — check before relying on them.
Frequently Asked Questions
Only when it has to. If the codecs inside Y4M (usually H.264 or H.265 for video, AAC for audio) are accepted by MJPEG, 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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Secure & 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.