Extract Audio from Y4M to WMA — Free Online Tool
Extract audio from Y4M (YUV4MPEG2) video files and convert it to WMA format using the wmav2 codec. Since Y4M is a raw, uncompressed intermediate format that typically carries no audio track, this tool is most useful in pipeline workflows where audio needs to be packaged separately into a Windows Media Audio file for distribution or archival.
to
FFmpeg Command
Copy this command to run the same conversion locally with FFmpeg on your desktop. Download FFmpeg
Drop your Y4M file here
or click to browse
Free — no uploads, no signups. Your files never leave your browser.
Settings
Note: Browser-based encoding uses approximate quality targets. For precise CRF compression, copy the FFmpeg command above and run it on your desktop.
Estimated output:
Conversion Complete!
DownloadHow It Works
Y4M is a raw uncompressed video container primarily used as an intermediate format for piping between video processing tools — and critically, it carries no audio data by default. When you supply a Y4M file that has been muxed with an audio stream, FFmpeg strips the raw video entirely (via the -vn flag) and encodes the audio into WMA format using the wmav2 codec at 128k bitrate. Because Y4M stores no compressed audio of its own, there is no audio 'copy' shortcut available here — the audio must be fully encoded from its raw PCM form into wmav2, Microsoft's second-generation Windows Media Audio codec. The result is a standalone .wma file ready for playback in Windows Media Player or any WMA-compatible application.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg command-line tool, which handles all media reading, processing, and encoding. In the browser version of this tool, FFmpeg runs via WebAssembly (FFmpeg.wasm) without any server involvement. |
-i input.y4m
|
Specifies the input file in Y4M (YUV4MPEG2) format — a raw, uncompressed video container used as an intermediate format in lossless video processing pipelines. FFmpeg reads the raw video frames and any accompanying audio stream from this file. |
-vn
|
Disables video output entirely, telling FFmpeg to ignore the raw YUV video frames in the Y4M file and produce an audio-only output. This is essential for extracting just the audio track without carrying unnecessary (and enormous) uncompressed video data into the WMA file. |
-c:a wmav2
|
Selects the wmav2 encoder for the audio stream — Microsoft's second-generation Windows Media Audio codec. wmav2 provides better compression efficiency than wmav1 and is the standard codec used inside .wma container files for modern Windows Media playback compatibility. |
-b:a 128k
|
Sets the audio encoding bitrate to 128 kilobits per second for the wmav2 output. This is a standard mid-quality bitrate that balances file size and audio fidelity; it is suitable for music and voice content. Increase to 192k or 256k for higher quality, or reduce to 64k for smaller voice-only files. |
output.wma
|
Specifies the output filename and format. The .wma extension tells FFmpeg to wrap the wmav2-encoded audio in an ASF (Advanced Systems Format) container — the underlying Microsoft container format used by all WMA files, which also supports metadata tags and optionally DRM. |
Common Use Cases
- Extracting audio from a Y4M file produced by a lossless video processing pipeline (e.g., AviSynth or VapourSynth output) to distribute the soundtrack separately as a WMA file for Windows-ecosystem users.
- Converting the audio track from a Y4M intermediate file into WMA for use with legacy Windows applications or devices that require Microsoft's proprietary audio format.
- Packaging audio from a Y4M master file into WMA for upload to older Windows Media streaming servers or SharePoint document libraries that expect .wma attachments.
- Archiving the dialogue or commentary track from a Y4M lossless edit as a compressed WMA file to reduce storage footprint while preserving a Windows-compatible format.
- Separating audio from a Y4M file generated during a video quality testing or comparison workflow so it can be reviewed independently in a Windows Media Player environment.
- Producing WMA audio assets from Y4M source files for use in legacy Windows game engines or multimedia authoring tools (e.g., older DirectShow-based applications) that natively support wmav2 streams.
Frequently Asked Questions
Standard Y4M files do not include an audio stream — the format was designed purely for raw uncompressed video interchange between tools like FFmpeg, x264, and VapourSynth. However, some workflows mux an audio stream into a Y4M container alongside the raw video, and FFmpeg can read it. If your Y4M file has no audio track, FFmpeg will produce an empty or error output. You can verify whether your file contains audio by running 'ffprobe input.y4m' before attempting extraction.
Y4M itself is lossless and uncompressed, but WMA (wmav2) is a lossy codec developed by Microsoft. The lossiness comes entirely from the output format: wmav2 uses perceptual audio compression that discards frequency information deemed inaudible by its psychoacoustic model. No amount of lossless input can prevent quality loss when encoding to a lossy codec like wmav2 — the output quality is determined by the chosen bitrate, defaulting here to 128k.
Replace the '128k' value in the '-b:a 128k' flag with your desired bitrate. For example, use '-b:a 192k' for higher quality audio or '-b:a 64k' for a smaller file. Supported wmav2 bitrates typically range from 64k to 320k. Higher bitrates preserve more audio detail but increase file size, while lower bitrates are useful for voice-only content where full fidelity is not required.
WMAv1 is Microsoft's original Windows Media Audio codec, while wmav2 is the second-generation version offering better audio quality at equivalent bitrates through improved compression algorithms. FFmpeg's default WMA codec is wmav2, and it is the more widely supported of the two in modern playback software. You can switch to wmav1 by replacing '-c:a wmav2' with '-c:a wmav1' in the command, but wmav2 is the recommended choice for virtually all use cases.
Y4M files do not carry metadata tags in any standardized way, so there is typically no title, artist, or album information to transfer to the WMA file. WMA natively supports metadata tags (stored as ASF attributes in the container), but since the source Y4M has none, the output WMA will be untagged. You can add metadata to the output by appending FFmpeg flags such as '-metadata title="My Track"' to the command before the output filename.
The FFmpeg command shown operates on one file at a time, but you can batch process multiple Y4M files using a shell loop. On Linux or macOS, run: 'for f in *.y4m; do ffmpeg -i "$f" -vn -c:a wmav2 -b:a 128k "${f%.y4m}.wma"; done'. On Windows Command Prompt, use: 'for %f in (*.y4m) do ffmpeg -i "%f" -vn -c:a wmav2 -b:a 128k "%~nf.wma"'. This is particularly useful for processing large batches of Y4M intermediate files from a render pipeline.
Technical Notes
Y4M (YUV4MPEG2) is an intentionally minimal container format — it carries raw YUV video frames with a simple header and was never designed to be a delivery format, which is why audio support is marginal at best. When audio is present in a Y4M file, it is stored as raw PCM, meaning FFmpeg must fully encode it into wmav2 rather than simply remuxing a compressed stream. The wmav2 codec encodes into an ASF (Advanced Systems Format) container with the .wma extension — ASF is Microsoft's underlying container, and it technically supports DRM, multiple streams, and metadata, though this tool produces a straightforward single-stream audio file. One known limitation is that wmav2 does not support all sample rates equally; unusual sample rates from the source PCM audio may be resampled automatically by FFmpeg. WMA files are natively supported on Windows without additional codecs but may require plugins or third-party players on macOS and Linux. If maximum compatibility is a concern for non-Windows targets, consider MP3 or AAC as alternative output formats.