ASF to AU Converter

ASF to AU Converter

ASF (Advanced Systems Format) is Microsoft's streaming container, usually holding a WMA audio track alongside WMV video. AU (.au, also .snd) is one of the oldest digital audio formats — Sun Microsystems' Unix sound format, classically 8-bit μ-law at 8000 Hz. This converter is an audio extraction: it pulls the audio out of the ASF, re-encodes it to AU, and discards any video. It exists mainly to feed legacy Unix, NeXT, or old Java systems that expect .au input.

ASF Format at a Glance

AU Format at a Glance

How to Convert ASF to AU

1. Upload Your ASF File: Drag and drop your .asf file onto the page or click "+ Add Files." You can queue several files to convert with the same settings.
2. Pick the Audio Codec: Under Advanced Options, set Audio Codec to PCM mu-law for a classic telephone-grade .au, or PCM 16-bit Little Endian for an uncompressed, higher-fidelity AU file.
3. Set Audio Sample Rate and Channel: Leave both at Original to preserve the source, or choose 8000 Hz / Mono to match the historical μ-law profile. Use Trim if you only need a section.
4. Convert and Download: Click "Convert" and download your AU file. No sign-up, no watermark. Files are uploaded over an encrypted connection, processed on our servers, and deleted automatically after a few hours.

Frequently Asked Questions

Does converting ASF to AU keep the video?

No. AU is an audio-only format, so the video stream is discarded during conversion. Only the audio track is extracted, re-encoded to AU, and saved. If you need to keep the picture, convert the ASF to a video format instead.

Will the AU file sound as good as the original ASF audio?

It cannot sound better, and often sounds worse. ASF usually carries lossy WMA, so detail is already gone — converting to AU cannot restore it. If you then pick 8-bit μ-law, you add a second lossy step at telephone quality. To minimize further loss, choose an uncompressed PCM codec (such as PCM 16-bit) at the original sample rate.

What is the difference between μ-law and PCM in an AU file?

μ-law (G.711) is an 8-bit companded encoding designed for telephone audio — small files, limited fidelity, and a lossy step. Linear PCM stores raw uncompressed samples (8, 16, 24, or 32-bit), so it is larger but does not throw away detail. The AU container can hold either; pick μ-law for compatibility with old systems and PCM when you care about quality.

What software can open a .au file?

Java applications open AU natively through AudioSystem, and it remains a de facto sound format on legacy Unix and NeXT systems. On the desktop, media players such as VLC and audio editors like Audacity also read .au. Because it is a niche legacy format, modern phones, browsers, and consumer apps frequently do not play it.

Should I really convert to AU, or to something more common?

For everyday playback and sharing, AU is rarely the right target — it is a legacy Unix/Java format. Convert ASF to MP3 for a small, near-universally compatible file, or convert ASF to WAV for a standard uncompressed track that works across editors. Choose AU only when a specific old system or toolchain requires .au input.

Is the AU format still maintained or standardized?

There is no actively maintained formal standard the way WAV or MP3 have. AU's structure — a 24-byte header, the .snd magic bytes, and a handful of encodings (μ-law, A-law, PCM, ADPCM) — has stayed stable for decades precisely because it is legacy. It persists mainly through Java's sound API and old Unix tooling rather than ongoing development.