Convert CAVS to AU — Free Online Tool
Convert CAVS video files to Sun AU audio format, extracting the AAC audio track and re-encoding it as uncompressed PCM (16-bit big-endian) — the native encoding for AU files used on Unix systems and legacy audio pipelines.
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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
CAVS files encode video using H.264 and audio using AAC, a lossy compressed format. Because AU files are audio-only containers that do not support video streams or compressed audio codecs like AAC, this conversion performs two operations: the video stream is discarded entirely, and the AAC audio is decoded and re-encoded as PCM signed 16-bit big-endian (pcm_s16be). This means the audio undergoes a lossy-to-lossless transformation in the sense that the output PCM is uncompressed, but any quality loss already introduced during the original AAC encoding in the CAVS file is permanent and cannot be recovered. The resulting AU file will be significantly larger than the audio portion of the source CAVS file because PCM stores raw, uncompressed waveform data.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg tool, the open-source multimedia processing engine that handles decoding the CAVS container, dropping the video stream, transcoding AAC audio to PCM, and writing the AU output file. |
-i input.cavs
|
Specifies the input file in CAVS format. FFmpeg reads the container, identifying the H.264 video stream and the AAC audio stream inside the CAVS file. |
-c:a pcm_s16be
|
Sets the audio codec for the output to PCM signed 16-bit big-endian, which is the native and default encoding for Sun AU files. This decodes the compressed AAC audio from the CAVS file into raw, uncompressed waveform data stored in big-endian byte order. |
output.au
|
Specifies the output filename with the .au extension, which signals FFmpeg to use the Sun AU muxer. Because AU is audio-only, the video stream from the CAVS input is automatically discarded without needing an explicit '-vn' flag. |
Common Use Cases
- Extracting a dialogue or narration audio track from a CAVS broadcast recording for use in a Unix-based audio processing pipeline that expects raw PCM in AU format
- Preparing audio samples from Chinese digital broadcast content (CAVS) for playback or analysis on legacy Sun Microsystems or early Unix workstations that natively support AU files
- Feeding audio extracted from CAVS source material into scientific or signal-processing software that reads AU files as a straightforward PCM container without needing to decode a compressed codec
- Archiving the audio channel of CAVS recordings as uncompressed PCM in AU format for use as a reference source in audio comparison or quality testing workflows
- Converting CAVS broadcast audio to AU for import into older Unix-era audio editors or tools that predate support for AAC or modern container formats
- Stripping video from a CAVS file and producing a clean, headerless-compatible AU audio file for streaming or embedding in legacy internet audio applications that historically used the AU format
Frequently Asked Questions
Not in the decoding step itself — the AU file stores audio as uncompressed PCM, which is technically lossless. However, the audio in your CAVS file was originally encoded as AAC, a lossy codec, so any quality degradation from that original compression is already baked in and cannot be undone. The resulting AU file will be a faithful, uncompressed representation of what the AAC codec preserved, not a restoration of the original pre-compression audio.
CAVS files use AAC audio compression, which typically achieves 10:1 or greater compression ratios over raw PCM. The AU format stores audio as uncompressed 16-bit PCM, so the audio data expands dramatically — a one-minute AAC track at 128k might be around 1 MB, while the equivalent PCM in AU format will be roughly 10 MB. The video stream from the CAVS file is also discarded, but the audio expansion is the dominant size factor.
Yes. The Sun AU format supports multi-channel PCM audio including stereo, so if your CAVS file contains a stereo AAC track, the output AU file will preserve the stereo channels encoded as interleaved 16-bit big-endian PCM samples. The channel count is carried through the conversion without modification by the FFmpeg command shown.
Yes. The AU format supports several PCM variants including pcm_s8, pcm_u8, pcm_alaw, and pcm_mulaw in addition to the default pcm_s16be. To use mu-law encoding, for example, replace '-c:a pcm_s16be' with '-c:a pcm_mulaw' in the FFmpeg command. Mu-law (G.711) was historically common in telephony and early Unix audio and produces smaller files at the cost of reduced dynamic range.
Add the '-ar' flag to resample the audio. For example, to output at 8000 Hz — the classic sample rate for AU files used in early Unix and internet audio — use: ffmpeg -i input.cavs -c:a pcm_s16be -ar 8000 output.au. The original CAVS AAC audio is likely at 44100 Hz or 48000 Hz, so specifying 8000 Hz will downsample it, reducing file size but also audio fidelity.
Yes, on the command line you can loop over files using a shell one-liner. On Linux or macOS: for f in *.cavs; do ffmpeg -i "$f" -c:a pcm_s16be "${f%.cavs}.au"; done. On Windows Command Prompt: for %f in (*.cavs) do ffmpeg -i "%f" -c:a pcm_s16be "%~nf.au". This processes each CAVS file in the current directory and produces a corresponding AU file. Note that the browser-based tool on this page handles one file at a time.
Technical Notes
The Sun AU format uses a straightforward fixed header followed by raw audio data, making it one of the simplest audio containers in widespread use. The default codec for this conversion, pcm_s16be, stores samples as signed 16-bit integers in big-endian byte order — AU's native byte order, inherited from the big-endian architecture of Sun SPARC workstations. The CAVS source file's AAC audio may have been encoded at various sample rates (commonly 44100 Hz or 48000 Hz) and channel configurations; all of these are passed through to the AU container as-is unless you explicitly specify '-ar' or '-ac' flags. Metadata such as titles or artist tags present in the CAVS container are not carried over, as AU's header supports only minimal metadata. There is no subtitle, chapter, or secondary audio track support in either format, so no information of those types will be lost silently. Because the video stream is simply dropped (not remuxed), the conversion is clean and leaves no stub video data in the output.