Convert VOB to AC3 — Free Online Tool
Extract and convert the AC3 Dolby Digital audio track from a VOB file into a standalone AC3 file, preserving the original surround sound encoding with no re-encoding quality loss. This is ideal for archiving DVD audio or feeding Dolby Digital audio directly into home theater systems and video editors.
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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
VOB files from DVD-Video discs store multiplexed streams — MPEG-2 video, AC3 Dolby Digital audio, subtitles, and navigation data all packed into a single container. This conversion demultiplexes the VOB and extracts just the AC3 audio stream, writing it into a raw AC3 file. Because the source audio in a VOB is almost always already encoded as AC3, FFmpeg can stream-copy or re-encode at the target bitrate with minimal processing. The video stream is discarded entirely. The result is a standalone Dolby Digital audio file that retains the original 5.1 surround channel layout from the DVD source.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg binary — the open-source multimedia processing engine that powers this conversion both in the browser via WebAssembly and locally on the desktop command line. |
-i input.vob
|
Specifies the input VOB file from a DVD-Video disc. FFmpeg parses the MPEG-2 Program Stream container and identifies all multiplexed streams, including MPEG-2 video, AC3 audio, and subtitle tracks. |
-c:a ac3
|
Sets the audio codec for the output to AC3 (Dolby Digital). Since the VOB source already contains AC3 audio, this encodes the extracted audio stream into a standard AC3 bitstream compatible with home theater receivers, broadcast systems, and authoring tools. |
-b:a 192k
|
Sets the AC3 output audio bitrate to 192 kilobits per second. For stereo DVD tracks this is a common DVD bitrate; for 5.1 surround content you may want to raise this to 448k or 640k to match the original DVD encoding and preserve all surround channel detail. |
output.ac3
|
Specifies the output filename with the .ac3 extension, which tells FFmpeg to write a raw Dolby Digital bitstream file. The video and subtitle streams from the VOB are automatically discarded since the AC3 format is audio-only. |
Common Use Cases
- Extract the Dolby Digital 5.1 surround sound track from a DVD VOB file to use as source audio in a video editing or mastering project
- Archive the original AC3 audio from a DVD rip separately from the video, reducing storage footprint while keeping lossless-relative audio fidelity
- Feed a standalone AC3 file into a home theater receiver or AV processor that accepts raw Dolby Digital bitstreams via S/PDIF or HDMI
- Strip the audio from a DVD concert or live performance VOB to create an AC3 audio track for remuxing into an MKV or MP4 container
- Prepare AC3 audio extracted from a VOB for broadcast or authoring workflows that require Dolby Digital as a deliverable format
- Isolate a specific language audio track from a multi-audio VOB file for subtitle translation or dubbing work
Frequently Asked Questions
If the VOB's audio track is already encoded as AC3 at or above your target bitrate, the quality loss is minimal — you are essentially re-encoding one lossy AC3 stream into another AC3 stream at 192k by default. For the highest fidelity, set the output bitrate to match the original DVD track, which is typically 192k, 224k, or 384k for stereo, and 448k or 640k for 5.1 surround. Avoid downgrading the bitrate below the source, as that compounds lossy compression artifacts.
Yes, as long as the source VOB contains a 5.1 AC3 track and your target bitrate is sufficient to carry all six channels, the channel layout is preserved in the output AC3 file. AC3 natively supports up to 5.1 channels, so no downmixing occurs by default. If you need to force a stereo downmix, you would add '-ac 2' to the FFmpeg command.
By default, FFmpeg selects the first audio stream it finds in the VOB. To extract a specific track — for example, the second audio stream — add '-map 0:a:1' to the command before the output filename, where the index is zero-based. You can inspect all available streams in the VOB by running 'ffmpeg -i input.vob' without an output file, which lists every video, audio, and subtitle stream with their indices and language tags.
Replace the value after '-b:a' with your desired bitrate. For a 5.1 surround track, common DVD values are 448k or 640k; for stereo, 192k or 256k is typical. For example, to encode at 448k use: ffmpeg -i input.vob -c:a ac3 -b:a 448k output.ac3. Setting a bitrate higher than the source provides no quality benefit, since the VOB audio is already lossy.
Yes. On Linux or macOS, use a shell loop: 'for f in *.vob; do ffmpeg -i "$f" -c:a ac3 -b:a 192k "${f%.vob}.ac3"; done'. On Windows Command Prompt, use: 'for %f in (*.vob) do ffmpeg -i "%f" -c:a ac3 -b:a 192k "%~nf.ac3"'. This processes each VOB in the current directory and writes a matching AC3 file. Batch processing from the command line is especially useful for large DVD rip collections that exceed the browser tool's 1GB file limit.
AC3 (Dolby Digital) is the native audio format stored inside DVD VOB files, making it the most direct and lossless-chain-preserving extraction target — no codec translation is needed. MP3 and AAC are different codec families that would require fully decoding the AC3 audio and re-encoding it, introducing an additional generation of lossy compression. If your downstream workflow specifically requires MP3 or AAC, those conversions are possible but will result in greater accumulated quality loss compared to staying within the AC3 format.
Technical Notes
VOB files follow the MPEG-2 Program Stream specification and frequently contain multiple AC3 audio streams at varying bitrates, typically between 192k and 640k, depending on whether the disc carries stereo or 5.1 surround tracks. When demuxing to a raw AC3 file, FFmpeg writes the Dolby Digital bitstream with standard sync frames; this format is directly playable by most AV receivers via digital coaxial or optical S/PDIF without a separate decoder. The output AC3 format does not support chapters, embedded subtitles, or multiple simultaneous audio tracks — it is a single-stream audio container. Metadata such as track title or language tags from the VOB are not preserved in the raw AC3 output. If the VOB contains LPCM or DTS audio rather than AC3, FFmpeg will transcode those streams to AC3 rather than demux them, which is a full decode-and-re-encode operation. For DVD content protected with CSS encryption, the VOB must first be decrypted using appropriate tools before FFmpeg can read it.