Extract Audio from WMV to AU — Free Online Tool
Extract audio from WMV video files and convert it to Sun AU format, decoding the WMV's WMA (wmav2) audio stream and re-encoding it as uncompressed 16-bit big-endian PCM — the native codec of the AU container. The result is a lossless-quality AU file suitable for Unix systems, legacy audio pipelines, and Java-based audio 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 typically carry audio encoded with WMA version 2 (wmav2), a lossy Microsoft proprietary codec. During this conversion, FFmpeg discards the video stream entirely and decodes the wmav2 audio to raw PCM samples in memory. Those samples are then re-encoded as 16-bit signed big-endian PCM (pcm_s16be) and wrapped in the Sun AU container — a minimal format consisting of a short fixed header followed by raw audio data. Because the intermediate step is full PCM decoding, the output represents the highest fidelity reconstruction possible from the original lossy WMA source. No further quality is lost after the WMA decode stage, though the original WMA compression artifacts are retained in the output since they were baked into the source.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg command-line tool, which handles all demuxing, decoding, encoding, and muxing steps in this conversion pipeline. |
-i input.wmv
|
Specifies the input WMV file. FFmpeg automatically detects the ASF container and the wmav2 audio codec (and any msmpeg4 video codec) inside, making both streams available for processing. |
-vn
|
Disables video output entirely, discarding the WMV's video stream so that only the audio is processed and written to the AU file. Without this flag, FFmpeg would attempt to include video in the output, which the AU container does not support. |
-c:a pcm_s16be
|
Decodes the WMA (wmav2) audio from the WMV and re-encodes it as 16-bit signed big-endian PCM — the standard and default codec for the Sun AU format, required for compatibility with Unix audio systems and Java's javax.sound API. |
output.au
|
Sets the output filename and triggers FFmpeg to use the Sun AU container format (detected from the .au extension), which wraps the pcm_s16be audio data with the minimal AU header structure. |
Common Use Cases
- Feed WMV lecture or webinar recordings into Unix-based audio processing pipelines that expect AU files as input, such as older signal processing or speech analysis tools.
- Extract a WMV audio track for use in Java applications, which have native javax.sound support for the AU/pcm_s16be format without requiring third-party libraries.
- Recover a clean PCM audio track from a WMV screen recording when you need to analyze or edit the waveform in a tool that does not support WMA-compressed audio.
- Convert WMV audio to AU for compatibility with legacy Sun workstation or early Unix multimedia software that predates modern compressed audio formats.
- Strip and archive the audio commentary from WMV video files in an uncompressed, format-agnostic form (pcm_s16be) that will remain readable without proprietary WMA decoders.
- Prepare WMV-sourced audio for import into NeXT/Sun-era audio editors or emulators that specifically require the AU container and PCM encoding.
Frequently Asked Questions
No — the source WMV file uses WMA (wmav2), which is a lossy codec, meaning some audio information was permanently discarded when the WMV was originally encoded. Converting to AU decodes the WMA stream to raw PCM, so no additional quality is lost during this conversion, but the compression artifacts already present in the WMA audio will still be audible in the AU output. The AU file will be a faithful, uncompressed representation of what the lossy WMA source contained.
WMV stores audio as WMA, a compressed lossy format that typically achieves 6–10x size reduction compared to uncompressed audio. AU with pcm_s16be stores raw, uncompressed 16-bit samples, so a one-minute WMA audio track at 128 kbps might occupy roughly 1 MB in the WMV, but the equivalent AU file will be approximately 10 MB (44100 samples/sec × 2 bytes × 2 channels × 60 seconds). This size increase is expected and not a sign of a problem with the conversion.
Yes, the Sun AU format supports multi-channel PCM audio including stereo, and pcm_s16be handles stereo tracks without issue. FFmpeg will preserve the channel count from the WMV source. However, AU does not support multiple independent audio tracks — if your WMV has more than one audio track (for example, multiple language streams), only the first track will be extracted by default.
By default, FFmpeg preserves the sample rate from the WMV source audio, which is commonly 44100 Hz or 48000 Hz for WMV files. The AU format supports standard sample rates including 8000, 11025, 22050, 44100, and 48000 Hz. If you need a specific sample rate — for example, 8000 Hz for telephony-style audio — you can add '-ar 8000' to the FFmpeg command before the output filename, e.g., 'ffmpeg -i input.wmv -vn -c:a pcm_s16be -ar 8000 output.au'.
Yes — the AU container supports several PCM variants including pcm_s8 (8-bit signed), pcm_u8 (8-bit unsigned), pcm_alaw (G.711 A-law), and pcm_mulaw (G.711 mu-law). You can substitute the codec by changing the '-c:a' value in the command, for example 'ffmpeg -i input.wmv -vn -c:a pcm_mulaw output.au' to produce a mu-law encoded AU file suitable for telephony applications. pcm_s16be is the default because it offers the best fidelity for general-purpose audio.
On Linux or macOS, you can loop over all WMV files in a directory with: 'for f in *.wmv; do ffmpeg -i "$f" -vn -c:a pcm_s16be "${f%.wmv}.au"; done'. On Windows Command Prompt, use: 'for %f in (*.wmv) do ffmpeg -i "%f" -vn -c:a pcm_s16be "%~nf.au"'. This applies the same extraction and pcm_s16be encoding to each file, outputting an AU file with the same base name alongside each original WMV.
Technical Notes
The Sun AU format uses a minimal fixed-length header (or optionally a variable header with annotation text) followed immediately by raw audio data, making it one of the simplest audio containers in existence. The pcm_s16be codec stores samples as 16-bit signed integers in big-endian byte order — note that this byte order is native to SPARC/big-endian Unix systems and differs from the little-endian PCM used in WAV files, so tools that read raw PCM must account for the byte order. WMV files using DRM (Digital Rights Management) protection cannot be processed by FFmpeg or this tool, as the encrypted content is inaccessible without the DRM license. Metadata from the WMV (such as title or artist tags stored in the ASF container) is not preserved in the AU output, since AU has extremely limited metadata support. If your WMV source was encoded at a low WMA bitrate (e.g., 64 kbps), the resulting AU file will be large but will not sound better than the compressed source — the AU format is not a quality upgrade, only an uncompressed representation of the decoded WMA data.