Convert WMV to AU — Free Online Tool
Convert WMV video files to AU audio format, extracting the audio stream and encoding it as 16-bit big-endian PCM — the native uncompressed format used on Unix and Sun Microsystems systems. This tool strips the WMV container and its WMA audio codec entirely, producing a raw PCM AU file suitable for Unix-based audio pipelines and legacy applications.
to
FFmpeg Command
Copy this command to run the same conversion locally with FFmpeg on your desktop. Download FFmpeg
Drop your WMV 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
WMV files store audio using Windows Media Audio codecs (typically WMAv2), wrapped in Microsoft's Advanced Systems Format (ASF) container. AU is a Sun Microsystems audio format that carries only raw PCM audio with a minimal header — it has no concept of video tracks. During this conversion, FFmpeg discards the video stream entirely (since AU cannot contain video), decodes the WMAv2 audio to raw PCM in memory, and then re-encodes it as 16-bit signed big-endian PCM (pcm_s16be) inside an AU container. Because WMAv2 is a lossy codec, the original audio quality is already bounded by whatever bitrate the WMV was encoded at — the PCM output is lossless in the sense that no further compression is applied, but it cannot recover detail lost during the original WMA encoding. The resulting AU file will be significantly larger than the source WMV audio track.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg command-line tool, which is running here as a WebAssembly (FFmpeg.wasm) instance entirely within your browser — no data is sent to a server. |
-i input.wmv
|
Specifies the input file as a WMV (Windows Media Video) file in Microsoft's ASF container. FFmpeg reads both the video stream and the WMAv2 audio stream from this file. |
-c:a pcm_s16be
|
Sets the audio codec to 16-bit signed big-endian PCM, which is the standard and default encoding for the AU format. This decodes the lossy WMAv2 audio from the WMV and re-encodes it as uncompressed PCM suitable for Unix audio systems. |
output.au
|
Specifies the output filename with the .au extension, which tells FFmpeg to use the Sun AU container format. The video stream from the WMV is implicitly dropped because the AU format supports only audio. |
Common Use Cases
- Feeding audio from Windows Media Video recordings into Unix or Linux audio processing tools (such as SoX or legacy DSP pipelines) that natively read the AU format
- Extracting speech or narration from WMV training videos or presentations for use with older Sun Microsystems or NeXT-based audio software that expects .au files
- Converting WMV audio tracks to uncompressed PCM AU for ingestion into scientific or academic audio analysis software that requires headerless or minimally-headered PCM data
- Archiving the audio content of WMV files in an uncompressed, platform-neutral PCM format before migrating away from Windows Media infrastructure
- Preparing audio extracted from WMV screencasts or recordings for use in Java applications, which historically used the AU format as their default audio format via javax.sound
Frequently Asked Questions
No — the output quality is capped by the original WMAv2 encoding in the WMV file. WMAv2 is a lossy codec, meaning audio detail was permanently discarded when the WMV was first created. Converting to PCM AU produces an uncompressed copy of that already-lossy audio; it does not recover any lost fidelity. The AU file will be larger, but it will not sound better than the source WMV audio.
WMV stores audio as compressed WMAv2, which achieves significant file size reduction through lossy compression — typically at 128 kbps or similar. AU with pcm_s16be is fully uncompressed, storing every audio sample as a raw 16-bit integer. At CD quality (44.1 kHz stereo), uncompressed PCM requires roughly 10 MB per minute, compared to under 1 MB per minute for compressed WMA audio. The video stream is also discarded, but the audio expansion more than compensates.
No. The AU format supports only a minimal annotation field in its header and has no standardized metadata tagging system comparable to ID3 or ASF metadata. Any title, author, copyright, or description metadata stored in the WMV's ASF container will be lost during this conversion. If metadata preservation is important, consider an intermediate format like FLAC or WAV before archiving.
Yes. The FFmpeg command uses pcm_s16be by default, but AU supports other encodings. You can substitute -c:a pcm_u8 for 8-bit unsigned PCM, -c:a pcm_alaw for G.711 A-law (common in telephony), or -c:a pcm_mulaw for G.711 mu-law. For example: ffmpeg -i input.wmv -c:a pcm_mulaw output.au. Note that 8-bit and mu-law/A-law encodings reduce file size but also reduce dynamic range compared to 16-bit PCM.
The displayed command processes a single file, but you can batch process on the command line using a shell loop. On Linux or macOS: for f in *.wmv; do ffmpeg -i "$f" -c:a pcm_s16be "${f%.wmv}.au"; done. On Windows PowerShell: Get-ChildItem *.wmv | ForEach-Object { ffmpeg -i $_.FullName -c:a pcm_s16be ($_.BaseName + '.au') }. Batch processing is particularly useful for large collections that exceed the browser tool's 1 GB per-file limit.
Yes, AU supports multi-channel PCM including stereo. If the WMV file contains a stereo WMAv2 audio track, FFmpeg will decode and write both channels into the AU file as interleaved 16-bit big-endian PCM samples. However, AU does not support multiple separate audio tracks — if your WMV contains more than one audio track, only the default (first) track will be included in the output.
Technical Notes
The AU format uses big-endian byte ordering (pcm_s16be), reflecting its origins on Sun SPARC workstations, which contrasts with the little-endian convention of Windows WAV files. This means AU files are not directly interchangeable with WAV PCM files at the byte level, even though both may carry 16-bit PCM audio. The WMV source uses the ASF container with the special -f asf flag in FFmpeg, but for this conversion FFmpeg auto-detects the input format, so no special input flags are needed. The video stream from the WMV is automatically dropped because AU has no video codec support and FFmpeg will not attempt to encode video into a container that cannot hold it. One known limitation is that AU's header encodes the sample rate and channel count but does not include a MIME type or extended metadata block, making it less descriptive than modern audio containers. If the source WMV was encoded with a non-standard sample rate (e.g., 22050 Hz rather than 44100 Hz), that sample rate will be preserved in the AU output without resampling unless you explicitly add a -ar flag to the command.