AU Player
Play Sun/NeXT AU (.au) audio files directly in your browser. Powered by FFmpeg WebAssembly. Open mu-law and linear PCM .au recordings without installing a codec.
Drop your audio file here
or click to browse
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What is AU Player?
The AU Player reads Sun/NeXT audio recordings, including mu-law and linear PCM samples. Drop a .au file onto the page and wait for local FFmpeg decoding. The recording becomes a stereo listening buffer with playback and seeking controls, without altering the original AU file.
How does AU Player work?
An AU header describes the encoding, sample rate, and channel count before the sample data. Tested inputs include 8 kHz mu-law and big-endian linear PCM. FFmpeg WebAssembly decodes them even when the browser's own decoder rejects the file.
The conversion stage creates 16-bit stereo PCM at 44.1 kHz, followed by Web Audio decoding at the browser audio-context rate. Mono reaches both channels. Upsampling an 8 kHz recording does not restore missing high frequencies, so telephone material still has a narrow bandwidth.
Key Features
- Reads the AU header for encoding, sample rate, and channels
- Decodes mu-law and linear PCM AU files with FFmpeg
- Prepares a 44.1 kHz intermediate WAV before browser decoding
- Mono files play on both channels
- Play, pause, and seek controls
- Decoding runs in WebAssembly on your device
Common Use Cases
Open an old Unix sound file
Play a .au file from an old workstation backup or archive that no current media player opens.
Listen to a telephony recording
Play an 8 kHz mu-law recording to hear what was captured on a phone system.
Check a legacy web sound effect
Preview a .au sound from an old website before you decide whether to keep or convert it.
Inspect a file before converting it
Listen first to confirm that an AU file is intact before you convert it to WAV or MP3.
Test audio output from a script
Play the .au file written by a program or a speech tool to hear what it produced.
How to Use This Tool
Choose an AU file
Click the upload area or drop a .au file onto it.
Wait for the decoder
The first file downloads the FFmpeg WebAssembly binary from a CDN. It stays loaded for the rest of the session.
Press play
Start playback to hear the decoded audio.
Seek or pause
Drag the progress control to jump to a position, or pause to stop where you are.
Pro Tips
- 1
Mu-law recordings at 8 kHz hold frequencies up to about 4 kHz. They sound muffled by design, and no player can restore the missing high end.
- 2
An .au extension does not identify the sample encoding on its own; the AU header distinguishes PCM from mu-law.
- 3
Use the WAV Player for .wav files, which the browser decodes without FFmpeg.
- 4
The player does not report the source sample rate. Its listening buffer can use the browser's rate after the intermediate WAV is decoded.
Frequently Asked Questions
How do I open an AU file?
Open the AU Player in a browser, choose the .au file, and press play. FFmpeg decodes it in WebAssembly, so no codec or desktop player is needed.
What is an AU audio file?
An AU file is an audio file in the Sun/NeXT format. It has a small header followed by the audio data, which is often mu-law or linear PCM.
Why does my AU file sound like a phone call?
Many AU files hold 8 kHz mu-law audio, the encoding used for telephone speech. That format keeps only the lower frequencies, so the sound is narrow and muffled.
What is the difference between AU and WAV?
Both can hold uncompressed PCM audio, but they use different headers. AU also commonly stores mu-law audio, while WAV files are usually linear PCM. Browsers play WAV natively, so AU files need a decoder.
What is mu-law audio?
Mu-law is an 8-bit companding scheme from telephony. It compresses each sample's range logarithmically to fit speech into 8 bits. This player decodes it to 16-bit PCM.