CONVERT Y4M → H264 (Y4M to H264)
Fast, secure Y4M to H264 conversion. No registration required.
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HOW TO CONVERT Y4M → H264
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 H264 container — no quality loss, near-instant finish.
Retrieve the H264
The H264 download is ready in seconds for stream-copy jobs, minutes for full transcodes.
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 H264. A Y4M to H264 conversion makes a recording portable. Video containers matter more than you might expect: players that handle H264 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. One more beat. Y4M is a video container, so playback depends on the codec inside as well as the wrapper itself. Receiving format: H264 is a video container, so playback depends on the codec inside as well as the wrapper itself.
Why convert Y4M to H264
Sending Y4M to someone on a non-matching operating system frequently leads to "file cannot be opened". H264 avoids that by sitting in the middle of everyone's compatibility list. The repackage runs quickly and without generational loss when codecs already align.
Y4M vs H264 — 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
- MIME Type
- video/x-raw-yuv
- Category
- Video Files
- Full Name
- YUV4MPEG2
- Conversion Engine
- FFMPEG
H264
- MIME type
- video/h264
- Extension
- .h264
- MIME Type
- video/h264
- Category
- Video Files
- Full Name
- H.264 Raw Stream
- Conversion Engine
- FFMPEG
- Extensions
- .h264, .264, .avc (raw bytestream)
- Standard
- ITU-T Rec. H.264 / ISO/IEC 14496-10 (AVC)
- Typical containers
- MP4, MKV, MOV, TS, FLV
- Profiles
- Baseline, Main, High, High 10, High 4:2:2, High 4:4:4
| Specification | Y4M | H264 |
|---|---|---|
| MIME type | video/x-yuv4mpeg2 | video/h264 |
| Extension | .y4m | .h264 |
| Pixel format | YUV 4:2:0, 4:2:2, 4:4:4 | — |
| Header | ASCII single line | — |
| MIME Type | video/x-raw-yuv | video/h264 |
| Category | Video Files | Video Files |
| Full Name | YUV4MPEG2 | H.264 Raw Stream |
| Conversion Engine | FFMPEG | FFMPEG |
| Extensions | — | .h264, .264, .avc (raw bytestream) |
| Standard | — | ITU-T Rec. H.264 / ISO/IEC 14496-10 (AVC) |
| Typical containers | — | MP4, MKV, MOV, TS, FLV |
| Profiles | — | Baseline, Main, High, High 10, High 4:2:2, High 4:4:4 |
Y4M vs H264 — 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.
H264 Strengths
- Universal hardware decode on every device since ~2010.
- 40-50% smaller than MPEG-2 at equal quality.
- Mature ecosystem with dozens of encoders (x264 is the open-source gold standard).
- Every browser, phone, TV, and car infotainment supports H.264.
- Supports everything from 144p vertical phone video to 8K HDR masters.
Limitations
- Patent-encumbered — encoding royalties apply for commercial use.
- 30-50% larger than H.265/AV1 at equivalent quality.
- Raw .h264 bytestreams have no timecode — containers (MP4/MKV) add that.
Quality & Compatibility
Resolution, frame rate and colour space are preserved end-to-end. If the H264 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 H264 when both containers support the same subtitle codec; otherwise burn the subtitles into the video first.
- For portrait (9:16) clips, make sure the H264 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; H264 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 H264, 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".
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.
H.264 Raw Stream
Target formatH.264 raw stream is an elementary bitstream containing only the video data encoded with the H.264/AVC codec without any container. It is commonly used as an intermediate format in video processing pipelines and for hardware encoder output.
Going the other way? Convert H264 back to Y4M with the same engine.
Common Use Cases
Share across platforms
Send H264 files to anyone without worrying about whether they have the right software for Y4M.
Embed in documents
Drop H264 output into Word, Google Docs, PowerPoint, Notion or a website without conversion warnings.
Optimize size
H264 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 H264 — Typical file sizes
Approximate file sizes for common scenarios.
- 10 sec 1080p Y4M ~600 MB
- 1 min 4K Y4M ~14 GB
- 1080p 30fps @ 5 Mbps (1 min) ~37 MB
- 4K 60fps @ 35 Mbps (1 min) ~260 MB
- HD streaming (1 hour, 6 Mbps) ~2.7 GB
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Related comparisons
See these formats side by side to understand which fits your use case best.
Related Guides
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