Convert VOB to M4B — Free Online Tool
Convert VOB files from DVD discs into M4B audiobooks, extracting and transcoding the AC3 audio track to AAC while preserving chapter structure for audiobook players. Ideal for turning DVD audio content — lectures, spoken word recordings, or language courses — into a portable audiobook format compatible with Apple Books, Overcast, and other podcast apps.
to
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 and AC3 (Dolby Digital) audio streams inside a DVD-Video container. Since M4B is a pure audio format with no video track, the video stream is completely discarded during this conversion. The AC3 audio — which VOB files use as their default codec — is not compatible with M4B, so it must be fully transcoded (re-encoded) into AAC, the native codec for MPEG-4 audio containers. The resulting M4B file uses the -movflags +faststart flag to place the MP4 metadata atom at the beginning of the file, enabling progressive playback and fast seeking in audiobook apps. Chapter markers supported by M4B can be defined separately if the source DVD had distinct title boundaries.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg binary, the open-source multimedia processing engine running in your browser via WebAssembly (FFmpeg.wasm) for this tool. |
-i input.vob
|
Specifies the input VOB file, which FFmpeg reads as a DVD-Video Object container holding multiplexed MPEG-2 video and AC3 audio streams. |
-c:a aac
|
Transcodes the audio stream to AAC, which is required because M4B's MPEG-4 container does not support the AC3 (Dolby Digital) codec found in VOB files. |
-b:a 128k
|
Sets the AAC audio bitrate to 128 kilobits per second, a reasonable default for speech-based audiobook content extracted from a DVD source. |
-movflags +faststart
|
Relocates the MOOV metadata atom to the start of the M4B file, enabling audiobook players like Apple Books to begin playback and seek through the file immediately without reading the entire file first. |
output.m4b
|
The output filename with the .m4b extension, which signals to Apple Books, Overcast, and other audiobook-aware players that the file supports bookmarking and chapter navigation. |
Common Use Cases
- Converting a DVD-based language course or audio lecture series into an M4B audiobook that can be loaded into Apple Books with chapter navigation and bookmarking
- Ripping a spoken-word or comedy DVD you own and converting it to M4B so you can listen on an iPhone or iPad without carrying physical media
- Transforming a DVD recording of a conference keynote or workshop into an M4B podcast episode compatible with Overcast, Pocket Casts, or Castro
- Extracting the narration audio from a DVD documentary for archival as an M4B audiobook, discarding the video to dramatically reduce file size
- Converting an old recorded stage production or radio drama preserved on DVD-Video into a portable M4B file for listening on long commutes
Frequently Asked Questions
No — M4B is a strictly audio-only format derived from MPEG-4, so the MPEG-2 video stream inside the VOB file is automatically discarded during conversion. Only the audio track is extracted and re-encoded to AAC. If preserving the video is important, you should target a different output format such as MP4 or MKV instead.
M4B files use the MPEG-4 container, which does not support AC3 (Dolby Digital) — the default audio codec in VOB files. Because there is no compatible pass-through option, FFmpeg must fully transcode the AC3 stream into AAC, which is the native and only widely supported lossy codec for M4B. This transcoding step does introduce a small amount of additional quality loss since you are going from one lossy codec to another, so choosing a higher bitrate like 192k or 256k can help compensate.
Adjust the -b:a flag to change the AAC bitrate. The default is 128k, which is adequate for speech-heavy content like audiobooks. For music or higher-fidelity source audio, increasing to 192k or 256k will noticeably improve quality: ffmpeg -i input.vob -c:a aac -b:a 256k -movflags +faststart output.m4b. Avoid going below 96k for AC3 sources, as the double-lossy transcoding from AC3 to low-bitrate AAC can produce audible artifacts, especially with multi-channel Dolby Digital input.
FFmpeg alone does not automatically map DVD title boundaries from VOB files into M4B chapter atoms, because VOB chapter data is stored at the IFO file level rather than inside the VOB container itself. To add chapters, you would need to create an FFmpeg chapter metadata file manually or use a tool like mp4chaps after conversion. If you are processing a full DVD, reading the VIDEO_TS folder with dvdnav or demuxing with tools like HandBrake first will give you better chapter control before the final M4B conversion.
M4B supports only stereo or mono AAC audio for maximum compatibility with audiobook players like Apple Books. FFmpeg will automatically downmix a 5.1 or other multi-channel AC3 stream to stereo AAC during transcoding. For spoken-word content this is completely transparent, but for VOBs containing music or cinematic audio, the downmix may collapse spatial effects. You can explicitly control this with -ac 2 in the command to force stereo output.
DVD chapters are often split across multiple VOB files (VTS_01_1.VOB, VTS_01_2.VOB, etc.). To concatenate them into one M4B, use FFmpeg's concat demuxer: create a text file listing each VOB path, then run ffmpeg -f concat -safe 0 -i filelist.txt -c:a aac -b:a 128k -movflags +faststart output.m4b. Alternatively, you can pass the entire VIDEO_TS folder directly with some FFmpeg builds using the dvd protocol, which handles the joining automatically.
Technical Notes
VOB files carry AC3 audio at bitrates typically between 192k and 448k, often in multi-channel configurations (2.0, 5.1). Transcoding to AAC at the default 128k represents a significant bitrate reduction, which is generally acceptable for mono or stereo speech but may be perceptible on music-heavy content. The M4B format is structurally identical to M4A but with the .m4b extension, which signals to Apple Books and compatible players that the file supports bookmarking and resume-on-open behavior. The -movflags +faststart flag moves the MOOV atom to the beginning of the output file, which is important for streaming and seeking in audiobook apps even for local files. M4B does not support subtitle streams, so any DVD subtitle tracks present in the VOB will be silently dropped. ID3-style metadata (title, author, cover art) can be added post-conversion with tools like AtomicParsley or ffmpeg's -metadata flags. If the source VOB is from a commercial DVD, be aware of DRM (CSS encryption) — FFmpeg cannot process encrypted VOB files directly, and decryption must be handled separately with tools like libdvdcss.