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, Audio Codec defaults to PCM mu-law — the classic telephone-grade .au encoding; switch it to PCM 16-bit Big Endian for an uncompressed, full-fidelity AU file (A-law is also available).
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 keep the default 8-bit μ-law, you add a second lossy step at telephone quality. To minimize further loss, switch the Audio Codec to PCM 16-bit Big Endian 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; μ-law is this converter's default and suits old systems, while switching to PCM 16-bit Big Endian is the choice 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.

Why is my AU file larger than the original ASF?

Because you are trading a compressed stream for raw per-sample storage. ASF usually carries lossy WMA, which packs audio into a small stream; even the default 8-bit μ-law AU stores a full byte per sample per channel (about 5.3 MB per minute at 44.1 kHz stereo), and PCM 16-bit doubles that, so the file can grow several times larger than the source. Choosing 8000 Hz mono μ-law is what keeps an AU truly small, at the cost of telephone-grade fidelity.

Can an AU file hold stereo audio?

Yes. The 24-byte AU header includes a channel-count field, so AU can store mono or stereo — and in principle more channels — in PCM, μ-law, or A-law. The classic 8 kHz μ-law AU associated with old Unix and Java is mono, but nothing in the format requires that; leave Audio Channel on Original to keep a stereo source in stereo.

Is my file kept private during conversion?

Your ASF upload travels over an encrypted connection, is processed on our servers, and is deleted automatically after a few hours. There is no sign-up, no watermark, and your files are never shared or made public.