Convert AU to AIFF — Free Online Tool
Convert Sun AU audio files to Apple AIFF format using a direct PCM-to-PCM stream transfer — no quality loss, no re-encoding. Both formats share the same default pcm_s16be codec, making this a clean lossless migration from Unix-era audio to a macOS-native container.
to
FFmpeg Command
Copy this command to run the same conversion locally with FFmpeg on your desktop. Download FFmpeg
Drop your AU file here
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Settings
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
AU and AIFF both store uncompressed PCM audio data, so this conversion is essentially a container swap rather than a transcoding operation. The tool reads the PCM audio stream from the AU file (encoded as 16-bit big-endian PCM, which is the AU default) and rewrites it into an AIFF container using the same pcm_s16be encoding. No audio samples are altered, decoded, or re-encoded — the raw audio data is preserved bit-for-bit. The AIFF container adds Apple-compatible metadata framing, including a COMM chunk describing the sample rate and channel count, and a SSND chunk holding the audio data itself. The resulting file is immediately compatible with macOS applications like Logic Pro, GarageBand, QuickTime, and the Finder's built-in audio preview.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg program — the same engine running in your browser via WebAssembly. The command is identical whether run locally on your desktop or executed in-browser. |
-i input.au
|
Specifies the input file in Sun AU format. FFmpeg detects the AU container from its magic number (0x2e736e64) and selects the appropriate demuxer automatically, reading the embedded sample rate, channel count, and PCM encoding type from the AU header. |
-c:a pcm_s16be
|
Sets the output audio codec to 16-bit signed big-endian PCM — the same encoding used by default in AU files and AIFF files. Since input and output codecs match, no transcoding occurs and the raw audio samples pass through unchanged, guaranteeing lossless conversion. |
output.aiff
|
Defines the output file as an AIFF container. FFmpeg infers the AIFF muxer from the .aiff extension and wraps the PCM audio stream in Apple's IFF chunk structure, producing a file natively compatible with macOS audio applications and the Apple ecosystem. |
Common Use Cases
- Importing legacy Unix workstation audio recordings or sound effects into Logic Pro or GarageBand, which prefer AIFF over the AU format
- Migrating a library of early internet audio samples (downloaded as .au files from 1990s websites) into a format that macOS Finder can preview and Spotlight can index
- Preparing AU-format audio assets from a NeXT or Sun workstation archive for use in a modern macOS audio production workflow
- Converting AU sound files exported by scientific or telephony software (which commonly outputs AU) into AIFF for archival in a professional audio asset management system
- Enabling AU-format voice recordings or speech samples to be opened directly in Apple's audio tools without needing third-party plugins or format bridges
- Standardizing a mixed collection of Unix system sounds (many distributed as .au) into AIFF for consistent metadata handling and compatibility across Apple devices
Frequently Asked Questions
No — this conversion is completely lossless. Both AU and AIFF store uncompressed PCM audio, and since both default to pcm_s16be (16-bit big-endian PCM), the audio data is transferred directly without any decoding or re-encoding. The waveform in the output AIFF file is mathematically identical to the waveform in the source AU file.
AIFF files carry slightly more container overhead than AU files. The AU format has a famously minimal header — as few as 24 bytes — while AIFF structures its data using IFF-style chunks (FORM, COMM, SSND, and optionally NAME or ANNO chunks) which add a small amount of framing data. The raw audio payload is identical in size; the difference is purely structural metadata.
The AU format supports an optional text annotation field in its header, but FFmpeg does not automatically map this to an AIFF ANNO or NAME chunk during this conversion. The audio data is preserved completely, but any embedded AU text annotations will not appear in the AIFF output. If preserving that text is important, you should note it separately before converting.
The command as written explicitly sets the output codec to pcm_s16be, so if your AU file contains mulaw or alaw compressed audio, FFmpeg will decode it to linear PCM and encode it as 16-bit big-endian PCM in the AIFF container. This is still a high-quality conversion — mulaw and alaw are low-bitrate telephony codecs, so the AIFF output will actually have higher dynamic range headroom than the source. You can confirm your AU file's codec by running ffprobe on it before converting.
Yes — AIFF supports pcm_s24be, pcm_s32be, pcm_f32be, and pcm_f64be, which AU does not. To convert to 24-bit AIFF, change the command to: ffmpeg -i input.au -c:a pcm_s24be output.aiff. Note that upsampling bit depth from a 16-bit source does not recover lost detail — it simply provides more headroom for further processing in a DAW without accumulating rounding errors.
On macOS or Linux, you can loop over all AU files in a directory with: for f in *.au; do ffmpeg -i "$f" -c:a pcm_s16be "${f%.au}.aiff"; done. On Windows (Command Prompt), use: for %f in (*.au) do ffmpeg -i "%f" -c:a pcm_s16be "%~nf.aiff". This applies the same pcm_s16be codec used by the browser tool and produces one AIFF file per AU input.
Technical Notes
The AU format (also called SND or .snd on NeXT systems) encodes audio with a minimal fixed header containing magic number, data offset, data size, encoding type, sample rate, and channel count. FFmpeg maps AU's encoding field directly to PCM codec identifiers, supporting signed 8-bit, unsigned 8-bit, signed 16-bit big-endian, A-law, and mu-law variants. AIFF, by contrast, uses Apple's IFF-derived chunk structure and supports a wider range of linear PCM bit depths (16, 24, 32-bit integer and 32/64-bit float). Because both formats store audio in big-endian byte order natively, no byte-swapping is required during this conversion — an efficiency advantage over converting to little-endian formats like WAV. One known limitation: AU files can technically encode mu-law or A-law audio, which are lossy telephony codecs; when those are encountered, FFmpeg decodes them to linear PCM for the AIFF output, which is the correct behavior but means the AIFF will not be a pure container remux. Sample rate and channel count metadata are faithfully preserved in the AIFF COMM chunk. AU files do not support chapters, multiple audio tracks, or embedded subtitles, and neither does AIFF, so there are no compatibility gaps in that regard.