Extract Audio from VOB to AU — Free Online Tool
Extract audio from VOB DVD files and save it as a Sun AU file, converting the AC3 (Dolby Digital) audio track to uncompressed 16-bit big-endian PCM. This tool is ideal for Unix/Linux workflows that require raw PCM audio from DVD source material without any lossy re-encoding artifacts beyond the original AC3 decode.
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FFmpeg Command
Copy this command to run the same conversion locally with FFmpeg on your desktop. Download FFmpeg
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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
VOB files store multiplexed MPEG-2 video alongside AC3 (Dolby Digital) audio streams, as used on DVD-Video discs. During this conversion, FFmpeg reads the VOB container, discards the MPEG-2 video stream entirely, and decodes the AC3 audio to raw PCM samples. Those samples are then written into the Sun AU container encoded as PCM signed 16-bit big-endian (pcm_s16be) — the AU format's default and most compatible codec. Unlike AC3, which is a lossy multi-channel format, PCM stores every decoded sample directly, so the output is an uncompressed representation of what the AC3 codec decoded. The AU format itself uses a minimal fixed header followed by raw audio data, making it trivially simple to parse on Unix systems.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg binary, the open-source multimedia processing engine running here as WebAssembly in your browser. All subsequent flags control how it reads, transforms, and writes your VOB audio. |
-i input.vob
|
Specifies the input file — a VOB (Video Object) from a DVD-Video disc. FFmpeg automatically detects the container and demultiplexes the interleaved MPEG-2 video, AC3 audio, and subtitle streams inside it. |
-vn
|
Disables video output entirely, telling FFmpeg to ignore the MPEG-2 video stream in the VOB. Since AU is a pure audio format with no video container capability, this flag ensures no video data is processed or written. |
-c:a pcm_s16be
|
Decodes the VOB's AC3 audio and re-encodes the samples as signed 16-bit big-endian PCM — the default and most compatible codec for the Sun AU format. Big-endian byte order matches the AU specification's native encoding, and 16-bit depth provides CD-quality dynamic range for the decoded Dolby Digital audio. |
output.au
|
Sets the output filename and signals to FFmpeg that the container should be Sun AU format, identified by the .au extension. FFmpeg writes the AU header with the correct sample rate (typically 48 kHz from DVD source) and channel count, followed by the raw PCM audio data. |
Common Use Cases
- Extracting a DVD's audio track on a Unix or Linux system where AU is the native audio format consumed by legacy tools like Sun's audio utilities or older SoX pipelines
- Archiving the decoded AC3 audio from DVD VOB files into uncompressed PCM for lossless further processing, avoiding generational quality loss from re-encoding to another lossy format
- Feeding raw PCM audio from a DVD source into Unix signal-processing or scientific audio analysis tools that expect the simple AU container format
- Stripping video from large VOB rips to produce lightweight audio-only files for transcription or dialogue review, while preserving maximum decoded audio fidelity
- Preparing DVD audio content for import into legacy audio workstations or Unix-based DAWs that natively support the AU/SND file format
- Isolating a specific audio track from a multi-audio-track VOB file (e.g., a commentary track) to decode and store as a flat PCM AU file for archival or comparison
Frequently Asked Questions
There is one decode step: the AC3 (Dolby Digital) audio stored in the VOB is lossy-compressed, so decoding it to PCM does not recover information that AC3 discarded during DVD authoring. However, the PCM stored in the AU file is a bit-perfect representation of the decoded AC3 output — no additional lossy encoding is applied. From this point forward the AU file is lossless, so any further processing you do in a Unix audio pipeline will not suffer additional compression artifacts.
VOB files store audio as AC3, a lossy compressed format typically at 192–448 kbps. The AU output uses uncompressed 16-bit PCM, which for stereo audio at 48 kHz (common on DVDs) requires roughly 1,536 kbps — several times the bitrate of AC3. Additionally, the VOB file also contained a large MPEG-2 video stream that is discarded, but the remaining audio portion expands significantly when decompressed to PCM. This size increase is expected and is the cost of storing fully uncompressed audio samples.
FFmpeg selects the first (default) audio stream in the VOB automatically. If your VOB contains multiple audio tracks — for example, a main feature track and a commentary — and you want to extract a specific one, you would need to run FFmpeg locally with the -map flag, such as adding '-map 0:a:1' to select the second audio stream. The browser-based tool uses the default stream selection, so for multi-track extraction you should copy the displayed FFmpeg command and run it on your desktop with the appropriate stream selector.
AU is a very old format associated with Sun Microsystems and early Unix systems. Most modern media players including VLC and QuickTime can open AU files, but consumer software support is inconsistent. The format is best suited for Unix/Linux tool pipelines, command-line processing with tools like SoX, or import into professional audio software. If you need broad playback compatibility, consider converting the AU file onward to WAV or FLAC, which carry identical PCM data in more universally supported containers.
The AU format supports several codecs beyond pcm_s16be, including pcm_alaw (G.711 A-law), pcm_mulaw (G.711 mu-law), pcm_s8, and pcm_u8. To switch, replace '-c:a pcm_s16be' in the command with your desired codec, for example: 'ffmpeg -i input.vob -vn -c:a pcm_mulaw output.au'. mu-law and A-law are 8-bit companded formats used in telephony and will produce much smaller files but at significantly reduced audio quality — they are lossy codecs optimized for voice, not music.
Yes. On Linux or macOS you can loop over VOB files in a shell: 'for f in *.vob; do ffmpeg -i "$f" -vn -c:a pcm_s16be "${f%.vob}.au"; done'. On Windows PowerShell: 'Get-ChildItem *.vob | ForEach-Object { ffmpeg -i $_.Name -vn -c:a pcm_s16be ($_.BaseName + ".au") }'. The browser tool processes one file at a time; the FFmpeg command is provided precisely so you can run batch jobs locally for large collections or files over 1GB.
Technical Notes
The Sun AU format imposes a straightforward binary structure: a 24-byte minimum header (magic number .snd, data offset, data size, encoding type, sample rate, channel count) followed by raw audio bytes. FFmpeg writes pcm_s16be samples in big-endian byte order, which is native to the AU specification and means no byte-swapping is needed on big-endian architectures. DVD VOB audio is commonly AC3 at 48 kHz sample rate; this sample rate carries through to the AU file, which is worth noting because some legacy Unix audio tools defaulted to 8 kHz and may need to be told the correct rate explicitly. Subtitle streams and chapter data present in the VOB are not mapped to the AU output — AU supports only a single audio stream with no metadata fields for titles, language tags, or timing cues. If the VOB contains Dolby Digital 5.1 (six-channel AC3), FFmpeg will decode all six channels and write them as six-channel PCM into the AU file; check that your downstream tool supports multi-channel AU, as some legacy Unix programs assume stereo or mono. The AU format has no defined maximum file size beyond filesystem limits, so even long DVD audio extractions fit cleanly.