CONVERT Y4M → FLV (Y4M to FLV)
Fast, secure Y4M to FLV conversion. No registration required.
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HOW TO CONVERT Y4M → FLV
Upload the Y4M
Drop your Y4M onto the uploader. Files up to 25 MB run on the free tier without registration; paid plans go up to 2 GB.
Stream-copy or re-encode
FFmpeg probes the codecs; if compatible, it stream-copies (no quality loss). Otherwise it transcodes at matching bitrate.
Download the FLV
Fetch the converted FLV as soon as it is ready. Both files auto-delete within two hours.
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 FLV. Repackaging a Y4M file into FLV is one of the fastest video jobs there is. When the codecs already match the target container specification, the bytes are literally copied across — no re-encoding, no quality drop, no long wait. Upload above and watch the progress bar usually fly. One more beat. Y4M is a video container, so playback depends on the codec inside as well as the wrapper itself. Receiving format: FLV is the Adobe Flash Video container, now deprecated but still lingering in archives.
Why convert Y4M to FLV
Flash Video is better supported than YUV4MPEG2 across web uploads, social networks and consumer devices. Converting trades the niche advantages of Y4M for broad playback and fewer "file type not supported" messages. Stream copy (when codecs match) keeps the video bit-identical to the source.
Y4M vs FLV — 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
FLV
- MIME type
- video/x-flv
- Extensions
- .flv, .f4v
- Video codecs
- Sorenson Spark, VP6, H.264 (F4V)
- Audio codecs
- MP3, Nellymoser, AAC
- Status
- Deprecated since December 31, 2020
| Specification | Y4M | FLV |
|---|---|---|
| MIME type | video/x-yuv4mpeg2 | video/x-flv |
| Extension | .y4m | — |
| Pixel format | YUV 4:2:0, 4:2:2, 4:4:4 | — |
| Header | ASCII single line | — |
| Extensions | — | .flv, .f4v |
| Video codecs | — | Sorenson Spark, VP6, H.264 (F4V) |
| Audio codecs | — | MP3, Nellymoser, AAC |
| Status | — | Deprecated since December 31, 2020 |
Y4M vs FLV — 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.
FLV Strengths
- Low overhead — the container is extremely compact.
- Designed for streaming — progressive download and seeking work well.
- Decoded natively by Flash Player on every OS for 20 years.
Limitations
- Flash Player is dead — no modern browser can play FLV without conversion.
- Legacy codecs (Sorenson, VP6) are poorly supported in modern tooling.
- Hardware video decoders never added FLV support.
Quality & Compatibility
Stream-copy is bit-perfect: when the codecs inside Y4M match what FLV can carry, the frames are copied across without re-encoding and the output is visually identical to the source. When transcoding is required, we target CRF 20–23 H.264 — visually transparent for most content — and keep audio bitrate at 192 kbps AAC.
Tips for Best Results
- Stream-copy beats re-encoding by orders of magnitude — check if your Y4M already uses FLV-compatible codecs before picking Advanced settings.
- For social uploads, 1080p at 30 fps strikes the best quality-to-size ratio; 4K is often downscaled server-side anyway.
- Keep the Y4M if you plan further editing — transcoded FLV is fine for final delivery but not for intermediate edits.
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 FLV, 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.
Flash Video
Target formatFLV was the dominant web video format during the Flash era. While Flash is now deprecated, many legacy video files still exist in FLV format and need conversion to modern formats.
Going the other way? Convert FLV back to Y4M with the same engine.
Common Use Cases
Share across platforms
Send FLV files to anyone without worrying about whether they have the right software for Y4M.
Embed in documents
Drop FLV output into Word, Google Docs, PowerPoint, Notion or a website without conversion warnings.
Optimize size
FLV 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 FLV — Typical file sizes
Approximate file sizes for common scenarios.
- 10 sec 1080p Y4M ~600 MB
- 1 min 4K Y4M ~14 GB
- 10-min YouTube 2008-era video 40-80 MB
- 45-min TV show (FLV H.264) 200-500 MB
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Related comparisons
See these formats side by side to understand which fits your use case best.
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