Convert MOV to AU — Free Online Tool
Convert MOV files to AU (Sun Audio) format by extracting the audio stream and encoding it as 16-bit big-endian PCM — the native lossless format for Unix systems. This tool strips away QuickTime's video, chapters, and multi-track metadata, delivering a raw uncompressed audio file compatible with legacy Unix applications and Sun Microsystems-era software.
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FFmpeg Command
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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
During this conversion, FFmpeg discards the video stream and any additional tracks (subtitles, chapters, secondary audio) from the MOV container entirely. The audio — whether it was AAC, MP3, Opus, FLAC, or Vorbis inside the QuickTime wrapper — is decoded and re-encoded as PCM signed 16-bit big-endian (pcm_s16be), which is the default and most compatible codec for the AU format. This is a full transcode of the audio, not a remux: compressed audio inside the MOV must be fully decoded to raw PCM samples before being written into the AU container. The AU format itself is extremely minimal — it uses a fixed 24-byte header followed by raw audio data — so all QuickTime metadata such as cover art, track titles, chapter markers, and spatial audio information is permanently dropped.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg program, which is running here as a WebAssembly binary (FFmpeg.wasm) entirely inside your browser — no data is sent to any server. |
-i input.mov
|
Specifies the input file as a MOV (QuickTime) container, which may contain video, compressed audio (such as AAC), chapter markers, and multiple tracks that FFmpeg will parse and make available for processing. |
-c:a pcm_s16be
|
Instructs FFmpeg to encode the output audio as PCM signed 16-bit big-endian, which is the native and most compatible audio encoding for the AU format and matches the byte order expected by Sun/SPARC Unix systems. |
output.au
|
Defines the output filename with the .au extension, which causes FFmpeg to write a Sun AU container. The video stream from the input MOV is automatically dropped because the AU format is audio-only with no video container support. |
Common Use Cases
- Preparing audio samples for playback on legacy Sun Microsystems workstations or Unix systems that rely on /dev/audio and the AU format natively
- Extracting raw uncompressed audio from a MOV-based professional video edit to feed into older Unix-based audio processing pipelines or command-line tools that only accept AU input
- Converting a QuickTime field recording to AU for use with Java applets or early Java audio APIs, which historically used AU as their primary supported audio format
- Stripping compressed AAC audio out of a MOV file and converting it to uncompressed PCM AU for bit-accurate analysis or archival on Unix systems without modern codec libraries
- Generating AU files from MOV screen recordings or voiceovers for integration into legacy Unix-based multimedia or e-learning authoring tools that predate widespread MP3/AAC support
- Extracting a clean lossless PCM copy of a MOV audio track for use as a reference signal in audio quality comparison or latency testing tools on Unix environments
Frequently Asked Questions
It depends on what audio codec is inside your MOV file. If the MOV contains lossless audio (such as FLAC or uncompressed PCM), the conversion to pcm_s16be AU will be lossless, assuming the bit depth does not exceed 16 bits. However, if your MOV contains compressed audio like AAC or MP3, those are lossy formats — decoding them and re-encoding to PCM does not recover the quality lost during original compression. The resulting AU file will be an accurate uncompressed representation of the already-compressed audio, but the original lossy artifacts remain.
Yes, the AU format supports mono and stereo audio. If your MOV contains a stereo audio track, FFmpeg will preserve the two channels in the output AU file encoded as pcm_s16be stereo. However, AU does not support surround sound or multi-channel audio beyond stereo in most implementations, so if your MOV contains 5.1 or spatial audio, only the first two channels may be retained or FFmpeg may down-mix depending on your settings.
All of them are discarded. The AU format supports only a single audio stream with no metadata beyond the most basic header fields — there is no container support for chapters, subtitle tracks, cover art, or secondary audio languages. FFmpeg will select the first (or best) audio stream from the MOV and encode only that to AU. If you need to convert a specific audio track from a multi-track MOV, you would need to add a flag like -map 0:a:1 to the FFmpeg command to select a particular stream.
MOV files typically store audio in compressed formats like AAC or MP3, which achieve significant size reductions compared to raw audio. The AU format stores audio as uncompressed PCM — every audio sample is stored at full resolution with no compression. A 3-minute AAC audio track at 128k bitrate might be around 2.8 MB inside the MOV, while the same audio as 16-bit stereo PCM at 44100 Hz in AU format would be approximately 30 MB. This size increase is expected and is the nature of converting from compressed to uncompressed audio.
You can replace pcm_s16be with another AU-compatible codec by changing the -c:a flag. Supported options include pcm_s8 (8-bit signed), pcm_u8 (8-bit unsigned), pcm_alaw (G.711 A-law, used in telephony), and pcm_mulaw (G.711 mu-law, common in North American phone systems). For example, to produce a mu-law AU file suitable for telephony use, you would run: ffmpeg -i input.mov -c:a pcm_mulaw output.au. Note that pcm_alaw and pcm_mulaw are lossy companded formats that reduce dynamic range significantly.
Yes, on the command line you can use a shell loop to process multiple files. On Linux or macOS, the command would be: for f in *.mov; do ffmpeg -i "$f" -c:a pcm_s16be "${f%.mov}.au"; done. On Windows Command Prompt, use: for %f in (*.mov) do ffmpeg -i "%f" -c:a pcm_s16be "%~nf.au". The browser-based tool on this page processes one file at a time, so for batch processing of large collections the local FFmpeg command is the recommended approach.
Technical Notes
The AU format (also known as .au or .snd) was developed by Sun Microsystems and uses a simple 24-byte header encoding the magic number, data offset, data size, encoding type, sample rate, and channel count — followed immediately by raw audio data. This simplicity made it the standard audio format on SunOS and Solaris systems and the default format for Java's early javax.sound API. The pcm_s16be encoding used by default stores samples as 16-bit signed integers in big-endian byte order, reflecting the big-endian architecture of SPARC workstations. MOV files, by contrast, are a complex QuickTime container that can carry multiple video and audio streams, time-coded chapter tracks, spatial metadata, and codec-specific parameter sets. Converting from MOV to AU is a destructive, one-way process in terms of metadata — nothing beyond the raw audio samples and the most basic stream parameters (sample rate, channels, encoding) survives. If your MOV file has a sample rate higher than 44100 Hz or uses floating-point audio, be aware that pcm_s16be will quantize the audio to 16-bit integer resolution. There is no concept of variable bitrate, tagging, or embedded images in AU, and most modern media players on macOS and Windows have limited or no support for the format without additional codecs.