Convert VOB to AU — Free Online Tool
Convert VOB files from DVD discs into AU audio format, extracting and transcoding the AC-3 or MPEG audio tracks into PCM signed 16-bit big-endian audio — the native encoding used by Sun AU. This is particularly useful for extracting clean, uncompressed audio from DVD content for use on Unix-based systems or legacy audio pipelines.
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DownloadHow It Works
VOB files are MPEG-2 program streams containing multiplexed video, AC-3 surround audio, subtitles, and menu data. During this conversion, FFmpeg demuxes the VOB container, discards the MPEG-2 video stream entirely (since AU is audio-only), and transcodes the default audio track — typically AC-3 at 192–448 kbps — into PCM signed 16-bit big-endian (pcm_s16be), which is the standard codec used in Sun AU files. This is a full decode-and-re-encode of the audio: the AC-3 compressed audio is fully decoded to raw PCM samples, resulting in an uncompressed waveform. The AU format uses a minimal fixed header storing sample rate, channel count, and encoding type, with no support for chapters, subtitle streams, or multiple audio tracks — so only the primary audio track is extracted.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg command-line tool, which handles all demuxing, decoding, and encoding operations in this conversion pipeline. |
-i input.vob
|
Specifies the input VOB file — a DVD Video Object container holding multiplexed MPEG-2 video, AC-3 audio, and optional subtitle streams. FFmpeg automatically detects the MPEG-2 program stream structure and identifies all contained elementary streams. |
-c:a pcm_s16be
|
Sets the audio codec for the output to PCM signed 16-bit big-endian, which is the standard encoding used in Sun AU files. This fully decodes the compressed AC-3 audio from the VOB and re-encodes it as uncompressed PCM samples in big-endian byte order. |
output.au
|
Specifies the output filename with the .au extension, which causes FFmpeg to use the Sun AU muxer. The AU container wraps the pcm_s16be audio with a simple binary header recording the sample rate, channel count, and encoding type. |
Common Use Cases
- Extracting dialogue or narration audio from a DVD lecture or educational disc for ingestion into a Unix-based audio processing pipeline that expects AU-format input
- Archiving the raw PCM audio from a DVD film's primary AC-3 soundtrack for analysis or editing in legacy Unix audio tools such as sox or audacity on older workstations
- Converting DVD audio tracks to AU format for playback or processing on Sun Solaris or other Unix systems where AU is the natively supported audio format
- Decoding AC-3 surround audio from a VOB file into uncompressed PCM AU for use as source material in audio forensics or academic audio research workflows
- Stripping audio from a homemade DVD recording (e.g., a family event recorded to DVD-R) to obtain an uncompressed audio file without any lossy codec artifacts beyond the original AC-3 decode
- Preparing audio content from DVD source media for streaming or serving over early Unix-era HTTP audio streaming infrastructure that relied on AU format
Frequently Asked Questions
The conversion involves one lossy step: decoding the AC-3 audio from the VOB file into raw PCM. AC-3 is a lossy codec, so the original compression artifacts from the DVD encoding are already baked into the audio. Once decoded to PCM and stored as AU (pcm_s16be), no further lossy compression is applied — the resulting AU file is uncompressed and represents the best fidelity achievable from that AC-3 source. If the VOB used a higher-bitrate AC-3 track (e.g., 448 kbps), the decoded audio will sound very close to the original.
VOB files store audio as AC-3, which is a compressed lossy format typically at 192–448 kbps. The AU output uses pcm_s16be, which is completely uncompressed. For a standard DVD with 2-channel 192 kbps AC-3 audio, the uncompressed PCM equivalent runs at roughly 1411 kbps — more than seven times larger. Additionally, the video stream from the VOB is discarded, so the AU file contains only audio, but that audio is significantly larger per second than the compressed original.
AU is a pure audio format with no support for video, subtitles, chapters, or multiple audio tracks. FFmpeg will automatically select the default (first) audio stream from the VOB and discard everything else, including the MPEG-2 video, any additional language audio tracks, and DVD subtitle streams. If you need a specific audio track from a multi-language DVD, you would need to add a stream selector flag like -map 0:a:1 to the FFmpeg command to choose a particular audio track by index.
Yes. The AU format supports several PCM encodings including pcm_mulaw (µ-law), pcm_alaw (A-law), pcm_s8, and pcm_u8, in addition to the default pcm_s16be. To use µ-law encoding, modify the command to: ffmpeg -i input.vob -c:a pcm_mulaw output.au. µ-law and A-law encodings produce smaller files but with reduced dynamic range, and are primarily useful for telephony or legacy systems expecting 8-bit compressed audio.
On Linux or macOS, you can use a shell loop: for f in *.vob; do ffmpeg -i "$f" -c:a pcm_s16be "${f%.vob}.au"; done. On Windows Command Prompt, use: for %f in (*.vob) do ffmpeg -i "%f" -c:a pcm_s16be "%~nf.au". This processes each VOB file in the current directory and outputs a corresponding AU file with the same base name. This is especially useful for ripping audio from multiple DVD chapter VOB files in sequence.
Yes, by default FFmpeg preserves the sample rate and channel configuration from the source VOB's audio track when writing the AU file. DVD AC-3 audio is typically 48000 Hz (48 kHz), so the output AU file will also be 48 kHz. Channel count — whether stereo, mono, or 5.1 surround — is also preserved unless you add explicit downmix flags. Note that the AU format's simple header stores these parameters directly, so playback tools that support AU will read them correctly.
Technical Notes
VOB files use the MPEG-2 program stream container and almost universally carry AC-3 (Dolby Digital) audio at 48 kHz, with bitrates ranging from 192 kbps (stereo) to 448 kbps (5.1 surround). The Sun AU format, standardized around RFC 2361, uses a compact binary header (24 bytes minimum) followed by raw audio samples with no compression beyond the selected PCM encoding. When FFmpeg writes pcm_s16be into an AU file, samples are stored as 16-bit signed integers in big-endian byte order — the natural byte order of SPARC and Motorola architectures for which AU was originally designed. A significant limitation of this conversion is that AU does not support multi-channel audio in a standardized way across all tools; while FFmpeg can write 6-channel (5.1) pcm_s16be into an AU container, many AU-compatible players will not interpret the channel layout correctly. For 5.1 source audio, consider downmixing to stereo by adding -ac 2 to the command. Metadata such as DVD track titles or language tags carried in the VOB are not preserved in the AU output, as the AU header has very limited metadata fields. No video data is retained in the output.