Y4M to FLV Converter
Processing entirely on your device — large files may take a moment.
YUV4MPEG2 Raw Video and Flash Video exist for different jobs: Y4M is uncompressed video with a text header — the interchange format of video-filter pipelines (avisynth/vapoursynth) and encoder test suites. Rescuing FLV recordings means converting them to MP4 before Flash compatibility disappears completely.
Because the whole conversion happens on your device, it is instant, unlimited and genuinely private — no accounts, no watermarks, no files on anyone's server. Multiple files are converted in one go.
How Y4M compares to FLV
| Y4M | FLV | |
|---|---|---|
| Compatibility | ffmpeg, x264, vapoursynth | Legacy players only |
| Best for | Filter-pipeline interchange | Early web video archives |
How to convert Y4M to FLV
- 1
Select your files
Drag & drop your Y4M files onto the area above, or click to browse. You can add multiple files at once for batch conversion.
- 2
Convert instantly
Click "Convert to FLV". The conversion runs entirely inside your browser using WebAssembly — no upload, no queue, no waiting.
- 3
Download results
Download each converted FLV file individually, or grab everything at once as a ZIP archive.
About the Y4M format
Y4M (YUV4MPEG2) is uncompressed video with a one-line text header: resolution, framerate and color space, then raw YUV frames. It is the lingua franca of video-filter pipelines — AviSynth, Vapoursynth and encoder test suites pass frames around as Y4M because there is nothing to misparse.
A Y4M of any real length is enormous (30MB per second of 1080p), so conversion to MP4/WEBM with H.264 or VP9 is always the destination — the value is in the zero-ambiguity input, not the format itself.
+ Strengths
- ✓Zero-ambiguity pixel format declaration
- ✓Standard between filter frameworks
- ✓Lossless by construction
! Limitations
- −No compression whatsoever
- −Color space variants (limited/full) trip decoders
- −Not natively playable in browsers
About the FLV format
FLV (Flash Video) was the video format of the early streaming web — YouTube's original delivery container from 2005 to ~2010, played by Adobe Flash Player. Later versions carried H.264/AAC, but the container lived and died with Flash, which reached end-of-life in 2020.
Modern browsers cannot play FLV at all, and only niche players (VLC) bother. If you have an FLV archive, converting to MP4 recovers the same H.264 video into a container every device accepts.
+ Strengths
- ✓Only relevant for early-web video archives
! Limitations
- −Dead ecosystem — Flash ended in 2020
- −No browser support at all
Why convert Y4M to FLV?
Think of it as moving your file to the container that fits the job. No compression whatsoever FLV works differently: Only relevant for early-web video archives If any of that sounds like your task, run the conversion — it takes seconds and nothing leaves your device.
Frequently asked questions
Is this Y4M to FLV converter really free?
Yes — completely free, with no sign-up, no watermark and no daily conversion limits. The site is supported by advertising.
Are my files uploaded to a server?
No. The conversion runs entirely inside your browser using WebAssembly, so your files never leave your device — that is what makes it instant and private.
Does it work on Windows, Mac, iPhone and Android?
Yes. Anything with a modern browser works: Windows, macOS, Linux, Android and iOS. No software installation is required.
Is there a file size limit for Y4M to FLV?
The only limit is your device's memory, since nothing is uploaded. Files up to a few hundred megabytes work fine on a modern desktop browser; very large files simply take a little longer.
Will the audio track be kept?
Yes. The audio is carried over and re-encoded to the standard audio codec of FLV, staying in sync with the video. If your Y4M file has multiple audio tracks, the first one is used.
Why is video conversion slower than image conversion?
Every frame has to be decoded and re-encoded. This site runs that work on your own CPU via WebAssembly — nothing is uploaded, but a multi-minute video reasonably takes a few minutes. Images, by comparison, are single-frame jobs.