Convert WMA to AU — Free Online Tool
Convert WMA (Windows Media Audio) files to Sun AU format, decoding the lossy wmav2-encoded audio and re-encoding it as uncompressed 16-bit big-endian PCM — the native codec of the AU container. This is useful for Unix/Linux workflows and legacy audio toolchains that expect raw PCM in the classic Sun Microsystems format.
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FFmpeg Command
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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
WMA files store audio as lossy wmav2 (or wmav1) compressed data inside Microsoft's proprietary ASF container. The AU format, developed by Sun Microsystems, is a simple header-based container designed to hold raw PCM audio. Because these two formats share no common codec, a full decode-and-re-encode is required: FFmpeg decodes the WMA bitstream to raw PCM samples in memory, then writes those samples as 16-bit signed big-endian PCM (pcm_s16be) into the AU container. The result is a lossless representation of the decoded audio — meaning no further compression loss occurs after the initial WMA decode, but the quality ceiling is already set by the original lossy WMA encoding. File sizes will increase substantially because uncompressed PCM at 16-bit/stereo is far larger than a compressed WMA file at the same duration.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg binary — the core multimedia processing engine that handles decoding the WMA input, converting the audio samples in memory, and muxing the result into the AU container. |
-i input.wma
|
Specifies the input file, a WMA file containing audio encoded with Microsoft's wmav2 (or wmav1) codec inside an ASF container. FFmpeg auto-detects both the container and the codec from the file. |
-c:a pcm_s16be
|
Sets the output audio codec to 16-bit signed big-endian PCM, which is the standard and most capable codec supported by the Sun AU container. This fully decodes the lossy WMA audio and stores the raw PCM samples in big-endian byte order as required by the AU format specification. |
output.au
|
Specifies the output filename with the .au extension, which tells FFmpeg to use the Sun AU muxer. The resulting file will have a minimal AU header followed by the raw pcm_s16be audio data, ready for use with Unix audio tools and any application that supports the AU format. |
Common Use Cases
- Feeding WMA audio into Unix-based audio processing pipelines (e.g., SoX, legacy DSP tools) that natively read AU files without requiring additional codec libraries
- Preparing audio assets for older Java applications or applets that used the AU format as their default supported audio type via the javax.sound API
- Archiving WMA audio in a simple, well-documented, header-minimal format for long-term storage on Unix systems where proprietary codecs may not be available in the future
- Converting DRM-free WMA files from a Windows Media Player library into AU format for use on a Sun Solaris or legacy Unix workstation audio environment
- Creating test audio fixtures in AU format for software that performs low-level PCM audio analysis, since AU's pcm_s16be encoding provides direct, unambiguous sample access
- Stripping Microsoft-proprietary encoding from WMA files when delivering audio to an audio engineering environment that standardizes on uncompressed PCM containers
Frequently Asked Questions
No. WMA is a lossy format, meaning audio quality is permanently reduced at the time of the original WMA encoding. Converting to AU produces uncompressed pcm_s16be output, which accurately preserves every decoded sample from the WMA file — but it cannot recover the detail lost during the original lossy compression. The AU file will be a lossless representation of already-lossy audio, so the quality ceiling is fixed by the original WMA bitrate.
WMA uses lossy compression (wmav2) that typically achieves ratios of 10:1 or more compared to raw PCM. The AU format stores audio as uncompressed 16-bit big-endian PCM with no compression whatsoever. A 5-minute WMA file at 128k bitrate might be around 4.8 MB, while the equivalent AU file at CD-quality (44.1 kHz, stereo, 16-bit) would be approximately 50 MB. This size increase is expected and not a sign that anything went wrong.
No. The Sun AU format has an extremely minimal header that includes only basic technical fields (sample rate, channel count, encoding type, and an optional ASCII annotation field). It has no support for rich metadata tags like artist, album, or title. Any ID3-style or ASF metadata present in the WMA file will be lost during conversion to AU.
Yes. The AU container supports several PCM-based codecs including pcm_mulaw, pcm_alaw, pcm_s8, and pcm_u8 in addition to the default pcm_s16be. To use µ-law encoding, for example, you would modify the command to: ffmpeg -i input.wma -c:a pcm_mulaw output.au. Note that µ-law and A-law are 8-bit companding formats historically used in telephony, and they will reduce audio fidelity compared to pcm_s16be.
Yes, with a shell loop. On Linux or macOS you can run: for f in *.wma; do ffmpeg -i "$f" -c:a pcm_s16be "${f%.wma}.au"; done. On Windows Command Prompt: for %f in (*.wma) do ffmpeg -i "%f" -c:a pcm_s16be "%~nf.au". The browser-based tool processes one file at a time, so the FFmpeg command shown on this page is especially useful for bulk conversions of large collections locally.
No. WMA supports DRM through Microsoft's PlayReady and older Windows Media DRM systems, and FFmpeg cannot decrypt DRM-protected WMA files. Only DRM-free WMA files will convert successfully. If you attempt to convert a DRM-protected file, FFmpeg will either produce an error or output silence. You must obtain a DRM-free version of the file to perform the conversion.
Technical Notes
The WMA format encodes audio using Microsoft's wmav2 codec (or the older wmav1), both of which are lossy transform codecs conceptually similar to MP3 or AAC but proprietary to Microsoft's ASF container. The target AU format is one of the oldest audio container formats still in use, developed by Sun Microsystems for SunOS/Solaris and adopted early on for internet audio delivery due to its trivial header structure. AU's default and most capable codec, pcm_s16be (16-bit signed big-endian PCM), is entirely lossless — big-endian byte order is a requirement of the AU spec and reflects the Motorola/SPARC architecture origins of the format. Because modern systems are predominantly little-endian (x86/x64), audio tools reading AU files must perform a byte-swap internally, which all compliant AU readers handle transparently. The AU format does not support DRM, chapters, subtitles, or multiple audio tracks. Sample rates are preserved from the source WMA file during conversion, so a 44.1 kHz WMA becomes a 44.1 kHz AU file. One practical limitation: AU files larger than 2 GB may cause issues with some legacy AU readers that use 32-bit offset fields in the header, though this is rarely a concern for typical audio content.