WebM to AU Converter

How to Convert WebM to AU Online

1. Upload Your WebM File: Drag and drop, paste a URL, or click "+ Add Files" to load one or more WebM clips. The page accepts WebM containers with either Vorbis or Opus audio (the two codecs allowed by the WebM spec).
2. Pick Sample Rate and Audio Channel: Defaults are Original (passes through the source rate and channel layout). Set Audio Sample Rate to 8000 Hz for classic mu-law telephony and Java applet compatibility, 22050 Hz for legacy Sun workstation audio, or 44100/48000 Hz for full-fidelity PCM. Set Audio Channel to Mono for voice payloads and 8 kHz mu-law, or Stereo for music and high-rate PCM.
3. Trim (Optional): Open the Trim panel and enter Start and Duration in hours:minutes:seconds.milliseconds to clip the AU to the segment you actually need — useful for voice prompts, lecture excerpts, or telephony IVR snippets.
4. Convert and Download: Click Convert. Files are uploaded over an encrypted connection, processed on our servers, and deleted automatically after a few hours — no sign-up, no watermark, never shared. The output is a true .au file with the .snd magic header (0x2E736E64) and audio/basic MIME type that Java AudioClip, Solaris audioplay, and FFmpeg all recognize.

Why Convert WebM to AU?

WebM is a modern web container holding Vorbis or Opus audio inside a Matroska-based wrapper, optimized for HTML5 <video> streaming. AU (Sun/NeXT audio, file extension .au or .snd, MIME audio/basic) is the opposite: a minimal 1992-era format with a 24-byte big-endian header, originally shipped with Sun Microsystems' SPARCstation /dev/audio device and adopted as the default sound format for NeXTSTEP and early Java applets. Converting WebM to AU extracts the audio track and re-encodes it into a format that legacy Unix tooling, embedded systems, and JVM-based players can decode without any extra codec library.

• Java AudioClip and Clip playback — javax.sound.sampled and the older java.applet.AudioClip API have historically guaranteed support for 8 kHz, 8-bit, mono mu-law AU. Convert a podcast clip from WebM to that exact profile and it will play in any JVM without bundling JLayer or Tritonus.
• Solaris and legacy Unix workstations — SPARC, AIX, and IRIX boxes treat .au as the native audio format; audioplay, sox, and play open it directly. WebM with Opus needs a recent FFmpeg build that older Unix shops may not maintain.
• Asterisk and FreeSWITCH IVR prompts — open-source PBX systems often ingest 8000 Hz mono PCM mu-law (G.711) for voice prompts. AU is a clean container for that payload, smaller than WAV's RIFF wrapper by 20-something bytes per file.
• Game audio for retro/indie engines — engines like Allegro 4 and SDL 1.2 read AU natively. Indie devs targeting MS-DOS, classic Mac OS, or NeXT-style demos use .au to ship voice clips that play without external decoders.
• Academic speech corpora — phonetics tools (Praat, Wavesurfer, ESPS/Waves+) standardized on AU decades ago for read-aloud and forced-alignment datasets. Extracting the audio from a WebM lecture recording into AU keeps it in the toolchain.
• Tiny header overhead — AU's 24-byte fixed header is the smallest of the common audio containers (WAV is 44 bytes, FLAC has a STREAMINFO block, Ogg pages add ~28 bytes each). For millions of short voice snippets, the savings add up.

WebM vs AU — Format Comparison

AU Encoding Quick Guide

Frequently Asked Questions

Why does my AU file sound muffled compared to the WebM source?

If you exported at 8000 Hz mu-law (the Java-applet default), you've band-limited to roughly 3.4 kHz — that's the G.711 telephony bandwidth and it intentionally clips everything above the human-voice range. Re-export at 44100 or 48000 Hz with 16-bit PCM (S16BE) to keep music-quality fidelity; mu-law was designed for speech, not Opus-encoded music.

What's the difference between .au and .snd?

They're the same format. Sun used .au and NeXT used .snd; both files start with the magic number 0x2E736E64 (the ASCII bytes ".snd"). Some Solaris tools still emit .snd, but audio/basic MIME and most modern decoders expect .au. You can rename either extension to the other and the file still parses.

Will my AU file play in a Java applet or modern JVM app?

Yes if you target the supported profile: 8000 Hz, 8-bit, mono, mu-law. java.applet.AudioClip historically guaranteed that profile; javax.sound.sampled decodes it without third-party SPI. Higher-rate PCM AU also works in modern Java Sound, but mu-law is the safest choice for cross-version compatibility — including older J2SE applets still embedded in industrial control panels.

Why is the AU file larger than the WebM, even though I shortened it?

WebM with Opus compresses at roughly 32-64 kbps for voice and 96-192 kbps for stereo music. AU with 16-bit PCM at 44100 Hz stereo is uncompressed at ~1411 kbps — roughly 10-40x larger per second. Switch to 8 kHz mu-law mono and AU drops to 64 kbps, which is comparable to a low-bitrate Opus voice stream.

Can browsers play AU files natively?

No. Chrome, Firefox, Edge, and Safari all dropped or never supported audio/basic playback for <audio> tags. AU is decoded by Java Sound, FFmpeg, VLC, Audacity, Praat, sox, and Solaris audioplay, but not by any HTML5 media element. If you need browser playback, use WebM to MP3 or WebM to WAV instead.

Is mu-law really still used in 2026?

Yes, in two big places: the global PSTN/SIP voice network still runs G.711 mu-law (North America/Japan) and A-law (Europe/most of the world) for narrowband calls, and a long tail of Java enterprise apps (IVR, kiosk software, industrial HMIs) ship with mu-law .au assets. Asterisk and FreeSWITCH treat 8 kHz mono mu-law as a first-class prompt format.

What sample rate and channel count should I choose?

For Java applet compatibility and telephony, pick 8000 Hz mono with mu-law. For Sun/NeXT-era music playback, 22050 or 44100 Hz mono/stereo with 16-bit PCM matches what those workstations originally output. For modern archival on Unix, 48000 Hz stereo at 24-bit PCM keeps full fidelity at the cost of ~280 KB per second.

Can I batch-convert a folder of WebM clips at once?

Yes. Drop multiple .webm files onto the upload area and each is converted with the same settings (sample rate, channel, trim window). For very large batches (hundreds of files) on a Unix workstation, FFmpeg's CLI is faster: ffmpeg -i input.webm -ar 8000 -ac 1 -c:a pcm_mulaw output.au. The browser tool is the easier path when you don't have FFmpeg installed or you're working from a locked-down corporate machine.

What happens to video, subtitles, and chapters in the WebM?

They're dropped. AU is an audio-only container — no video track, no subtitles, no chapters, no cover art, no metadata beyond the optional annotation field in the header. If you need to keep the video, convert to a video container instead; if you want lossless audio with metadata, WebM to FLAC preserves tags. If your goal is the reverse direction, see AU to WAV or AU to MP3.