Y4M to CAF Converter
FileFlip converts Y4M to CAF entirely inside your browser, using FFmpeg compiled to WebAssembly. The file is never uploaded to a server: it is read off your disk, converted on your own machine, and saved back by the browser. That means no file-size limit, no queue and no account.
How do I convert a Y4M file to CAF?#
- Drop your Y4M file onto the converter at the top of this page, or click it to pick one from your computer. You can add as many as you like.
- Leave the target set to CAF and the conversion starts on its own. FileFlip downloads 30.8 MB of WebAssembly the first time and nothing after that, then runs FFmpeg on your own machine.
- Save the CAF file. Your browser writes it straight to your downloads folder, because there was never a server holding it.
Does converting Y4M to CAF lose quality?#
It depends on what is inside the file. Y4M is a container rather than a codec, so whether the CAF conversion copies the streams across untouched or re-encodes them is decided by the codecs that particular file happens to use.
Is it safe to convert Y4M files online?#
Yes, because nothing is uploaded. FileFlip converts Y4M files inside the browser tab you already have open, using WebAssembly builds of the same engines a desktop converter would install. Your file is read from your own disk into the page's memory, and no request carrying it is ever made.
You do not have to take that on trust. Open your browser's network panel, run a conversion, and you will see the engine come down and your file go nowhere. There is no upload, no server-side copy, no retention window, and no account tied to what you converted.
How FileFlip works lists every engine, its version and its download size, and shows how to check for yourself that nothing leaves your machine.
What Y4M to CAF actually does to the file#
Converting Y4M to CAF runs on FFmpeg, downloads 30.8 MB of WebAssembly the first time and nothing after that, re-encodes or copies through depending on the codecs in the file, and drops encoded streams and video tracks.
| Engine | FFmpeg |
|---|---|
| Conversion path | One step: Y4M → CAF |
| Downloaded to your browser | 30.8 MB, once, then cached by your browser |
| Quality | Decided by the codecs inside the file |
| You get back | One file |
| Where it runs | In a background worker, so the page stays responsive |
What survives the conversion
| What is in the file | This conversion | Why |
|---|---|---|
| Encoded streams | Dropped | The target format has nowhere to put it. |
| Video tracks | Dropped | The target format has nowhere to put it. |
What is a Y4M file?#
A Y4M file holds YUV4MPEG2 data, raw uncompressed video frames in planar YCbCr with a short plain-text header, the format codec developers feed into encoders like x264, x265 and vpxenc so nothing but the codec under test touches the pixels.
Use Y4M when testing or comparing video encoders, where the point is to remove every other codec from the pipeline so the one under test is the only variable.
Convert Y4M to a compressed format like MP4 for anything other than encoder testing, since the raw size makes it impractical to store or share.
What is a CAF file?#
A CAF file holds audio in Apple's Core Audio Format, introduced in 2005 to replace AIFF and WAV on the Mac because its 64-bit chunk sizes have no practical file size or duration limit.
Keep audio as CAF while it stays inside Apple's own tools, such as Logic Pro, GarageBand, or an iOS app's own audio recordings, where the format's size and codec flexibility are used directly.
Convert CAF to WAV or M4A when the audio needs to leave the Apple ecosystem, since most non-Apple software has no built-in way to open it.
Y4M to CAF questions people ask#
Why is a Y4M file so much bigger than the video it represents?
A Y4M file stores every pixel of every frame with no compression at all, unlike MP4 or MKV, which is exactly the point: encoder developers use it as clean, unaltered input so nothing but the codec being tested affects the result. A minute of 1080p footage can run to several gigabytes.
What is Y4M used for?
Y4M is the standard input format for testing and benchmarking video encoders such as x264, x265 and libvpx, because raw, uncompressed frames guarantee the encoder is working from an unaltered source rather than one already degraded by another codec.
Does a Y4M file have sound?
No, Y4M carries video only. It was designed purely as a way to pipe raw frames between video tools, with no provision for an audio track at all.
What creates a CAF file?
CAF files come from Apple's own audio software, including Logic Pro, GarageBand, and any iOS or macOS app that records audio through Apple's Core Audio APIs. Apple adopted CAF as its own format specifically to avoid the 4 GB size limit that WAV and AIFF both carry.