Free online AU to AIFF converter

Legacy Unix, Sun/NeXT, Java, or game audio may be supplied as .au, while a Mac-oriented editor, sampler, or delivery requirement accepts AIFF instead. Conversion creates a file the target software can identify as AIFF; it does not improve the source recording.

AU format

AU, also called Sun/NeXT audio, is an audio container developed by Sun Microsystems. Files usually use .au or .snd and commonly start with the signature .snd.

AU appears in Solaris and other Unix-era software, NeXT-derived systems, Java resources, and older multimedia assets. It can contain uncompressed signed PCM, 8-bit G.711 μ-law or A-law, floating-point audio, and other legacy encodings; an AU extension alone does not establish the codec, sample rate, bit depth, or channel count.

AIFF format and advantages

AIFF, Apple’s Audio Interchange File Format, is normally stored as .aif or .aiff. Standard AIFF stores uncompressed PCM samples, conventionally in big-endian byte order, with defined sample rate, channel count, and bit depth.

AIFF is supported by many macOS applications, DAWs, audio editors, and hardware samplers. It can also store markers and metadata chunks. If a program specifically requests AIFF, create standard PCM AIFF rather than AIFF-C/AIFC unless that program explicitly supports the compressed AIFF variant.

Convert an AU file to AIFF

Use the converter on 101convert.com to convert the file without installing software: upload the .au file, select AIFF as the output format, start the conversion, and download the resulting .aiff file. Do not rename input.au to input.aiff; changing an extension does not change the container or audio codec.

For local, repeatable conversion, FFmpeg can decode most AU variants and write standard 16-bit PCM AIFF:

ffmpeg -i input.au -c:a pcm_s16be output.aiff

Use 24-bit PCM when the source has higher than 16-bit integer precision and the destination supports it:

ffmpeg -i input.au -c:a pcm_s24be output.aiff

Audacity provides an interactive alternative. Open the AU file, choose File → Export Audio, select AIFF (Apple/SGI) as the format, select the required sample encoding, and save the file with an .aiff extension. Set the project or export sample rate before exporting when the receiving device specifies one.

Quality and compatibility checks

An uncompressed PCM AU file can be transferred to AIFF without changing its audio samples only when the conversion retains compatible sample rate, channel count, and bit depth. Converting 24-bit or floating-point audio to 16-bit PCM reduces stored precision; resampling or changing stereo to mono also changes the audio data.

Many AU files contain 8-bit μ-law, often at 8 kHz mono. Decoding μ-law to 16-bit PCM AIFF improves compatibility, but cannot restore detail removed by μ-law companding or the original low sample rate. Standard PCM AIFF will also usually be larger than a μ-law AU file.

Inspect the source before choosing export settings when compatibility matters. FFmpeg can report the detected codec and stream properties:

ffprobe -v error -select_streams a:0 -show_entries stream=codec_name,sample_rate,channels,bits_per_raw_sample -of default=nw=1 input.au

Some samplers accept only 16-bit, 44.1 kHz, mono AIFF. Apply those requirements explicitly rather than relying on defaults:

ffmpeg -i input.au -ac 1 -ar 44100 -c:a pcm_s16be output.aiff

Open the converted file in the intended application to confirm that its AIFF variant, sample rate, channel layout, and bit depth are accepted.