Convert Y4M to WMA — Free Online Tool
Convert Y4M (YUV4MPEG2) video files to WMA audio by extracting and encoding the audio stream using the wmav2 codec at 128k bitrate. This tool is ideal for pulling Windows Media Audio output from uncompressed intermediate video files used in professional video pipelines.
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FFmpeg Command
Copy this command to run the same conversion locally with FFmpeg on your desktop. Download FFmpeg
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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 format that carries no audio compression — it stores YUV pixel data frame-by-frame and is typically used as a lossless intermediate between video processing tools. Because Y4M files contain no audio stream by definition (audio is not part of the YUV4MPEG2 specification), this conversion extracts whatever audio FFmpeg can associate with the input and encodes it to WMA using the wmav2 codec. In practice, Y4M files piped from tools like x264 or libvpx may carry audio data alongside the raw video. FFmpeg discards the raw video stream and encodes only the audio into a WMA container using lossy wmav2 compression at 128kbps, producing a compact Windows Media Audio file.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg command-line tool, which handles all the demuxing, decoding, encoding, and muxing steps needed to convert the Y4M input into a WMA audio file. |
-i input.y4m
|
Specifies the input Y4M file. FFmpeg reads the raw YUV video frames and any associated audio data from this uncompressed YUV4MPEG2 source file. |
-c:a wmav2
|
Sets the audio codec to wmav2 (Windows Media Audio version 2), the default and higher-quality of the two WMA codec variants, used to encode the audio stream into the proprietary Microsoft WMA format. |
-b:a 128k
|
Sets the audio bitrate to 128 kilobits per second for the wmav2 encoder, balancing file size and audio fidelity — a standard quality level for WMA audio suitable for general listening and distribution. |
output.wma
|
Defines the output filename and tells FFmpeg to write the encoded wmav2 audio into a WMA container, the proprietary Microsoft format used for Windows Media Player and Windows-ecosystem audio distribution. |
Common Use Cases
- Extracting an audio commentary track from a Y4M intermediate file produced during a multi-pass video encoding workflow for distribution as a standalone WMA file
- Converting Y4M files generated by open-source video tools (such as those piped from AviSynth or VapourSynth) to WMA for playback on Windows Media Player or legacy Windows devices
- Archiving the audio component of an uncompressed Y4M master file as a lightweight WMA file for review or client approval without sharing the large raw video
- Preparing audio output from a Y4M intermediate for upload to platforms or enterprise systems that specifically require Windows Media Audio format
- Stripping and converting audio from Y4M files used in broadcast or post-production pipelines into WMA for use in Microsoft-ecosystem digital asset management systems
- Quickly generating a WMA audio preview from a Y4M file during a lossless video editing session without re-encoding the full video
Frequently Asked Questions
The official YUV4MPEG2 specification does not include an audio stream — Y4M is purely a raw video format. However, some tools and pipelines produce Y4M files with accompanying audio data or pass audio through alongside the video pipe. If your Y4M file has no audio, FFmpeg will produce an empty or very short WMA file. You should verify your source file contains audio before converting.
Y4M stores raw, uncompressed YUV video frames with no compression at all, making files extremely large — often several gigabytes per minute. The WMA output contains only the audio stream encoded with lossy wmav2 compression at 128kbps, discarding all video data entirely. The size reduction is dramatic because you are going from uncompressed multi-channel pixel data to a compressed audio-only file.
The audio bitrate is controlled by the '-b:a' flag in the command. Replace '128k' with your desired bitrate — for example, use '-b:a 192k' for higher quality or '-b:a 64k' for a smaller file. Supported bitrate options for wmav2 include 64k, 96k, 128k, 160k, 192k, 256k, and 320k. Higher bitrates preserve more audio detail but increase file size.
Yes. You can substitute '-c:a wmav1' in place of '-c:a wmav2' in the FFmpeg command. wmav1 is an older codec with slightly lower audio quality at equivalent bitrates and is intended for compatibility with very early Windows Media Player versions. For most modern use cases, wmav2 is the better choice as it is still widely supported and produces better audio quality.
Y4M files contain very limited metadata — typically just frame rate, resolution, and colorspace information embedded in the file header, with no standard support for title, artist, or album tags. The WMA container does support rich metadata tags, but since there is no audio metadata in the Y4M source to carry over, the output WMA file will have no embedded tags unless you add them manually using FFmpeg's '-metadata' flag.
The single-file command shown on this page can be adapted for batch processing using a shell loop. On Linux or macOS, you can run: for f in *.y4m; do ffmpeg -i "$f" -c:a wmav2 -b:a 128k "${f%.y4m}.wma"; done. On Windows Command Prompt, use: for %f in (*.y4m) do ffmpeg -i "%f" -c:a wmav2 -b:a 128k "%~nf.wma". This is especially useful for files over 1GB that exceed browser-based processing.
Technical Notes
Y4M (YUV4MPEG2) is one of the few truly uncompressed video formats with a defined, tool-agnostic header structure, making it a popular interchange format between applications like FFmpeg, x264, VapourSynth, and AviSynth. However, audio is not part of the Y4M spec, which means most Y4M files encountered in the wild will produce no WMA output — only files from pipelines that explicitly carry audio alongside Y4M video data are suitable for this conversion. The WMA output uses the wmav2 codec, which is a proprietary Microsoft codec offering reasonable audio quality at low bitrates but lacking the open-source ecosystem support of formats like AAC or Opus. WMA files are not natively supported on macOS or iOS without additional software, and modern streaming platforms generally do not accept WMA uploads. WMA does support DRM (Digital Rights Management) at the container level, though FFmpeg does not apply DRM by default. If your goal is broad compatibility rather than Windows ecosystem integration, consider targeting MP3 or AAC instead of WMA for the audio output.