Convert VOB to AMR — Free Online Tool
Convert VOB files from DVD discs into AMR audio, extracting the AC3 or MPEG audio track and re-encoding it to the Adaptive Multi-Rate Narrowband format optimized for speech. This is particularly useful for pulling dialogue, narration, or voice content from DVD recordings into a compact, mobile-compatible audio format.
to
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 are MPEG-2 program streams containing multiplexed video, AC3 surround audio, subtitles, and sometimes multiple audio tracks. During this conversion, FFmpeg demuxes the VOB container to isolate the default audio track, discards the MPEG-2 video stream entirely (since AMR is audio-only), and re-encodes the audio using the libopencore_amrnb codec at 12200 bps — the highest AMR-NB bitrate. AMR-NB is a narrowband codec engineered for speech signals sampled at 8 kHz, so the AC3 audio (typically 48 kHz, stereo or surround) is downmixed to mono and downsampled to 8 kHz in the process. This means music, sound effects, and wide-frequency content will sound noticeably degraded, but spoken dialogue retains intelligibility well.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg binary. In this browser tool, FFmpeg runs locally via WebAssembly (FFmpeg.wasm) with no file upload; on your desktop, this calls your locally installed FFmpeg executable directly. |
-i input.vob
|
Specifies the input VOB file — a DVD Video Object containing multiplexed MPEG-2 video, AC3 audio, and potentially subtitle and menu data. FFmpeg will demux all streams from this container before processing. |
-c:a libopencore_amrnb
|
Sets the audio encoder to libopencore_amrnb, the open-source implementation of the AMR Narrowband codec. This encoder will re-encode the DVD's AC3 audio track into AMR-NB format, automatically enforcing the 8 kHz mono constraints required by the codec. |
-b:a 12200
|
Sets the AMR-NB bitrate to 12200 bps, which corresponds to the highest quality mode available in AMR Narrowband (MR122). For speech extracted from DVD audio, this gives the best intelligibility the AMR-NB format can deliver. |
output.amr
|
Defines the output filename with the .amr extension. FFmpeg recognizes this extension and writes a raw AMR file containing only the encoded narrowband audio stream — no video, subtitles, or DVD structural data are included. |
Common Use Cases
- Extracting a recorded lecture, sermon, or spoken-word presentation from a DVD to create a small AMR file compatible with older mobile phones and voice memo apps.
- Pulling narration or commentary tracks from DVD documentary discs for use in voice transcription pipelines that accept AMR input.
- Converting DVD-recorded court proceedings or interviews into AMR format for archiving in telephony-oriented case management systems.
- Extracting dialogue from a VOB file to test speech recognition engines that were trained on narrowband 8 kHz telephone audio.
- Creating compact voice samples from DVD training materials to distribute to field staff with low-storage-capacity feature phones.
- Stripping the audio from a DVD menu or instructional VOB to produce a small AMR prompt file for an IVR (Interactive Voice Response) system.
Frequently Asked Questions
No — AMR-NB is specifically engineered for human speech at an 8 kHz sample rate, which captures roughly the 300 Hz–3400 Hz telephone frequency range. DVD audio, typically encoded in AC3 at 48 kHz with full stereo or surround sound, will be drastically downsampled and downmixed to mono. Music, sound effects, and any content with significant high-frequency or stereo information will sound thin, muffled, and degraded. This conversion makes sense only when the VOB's audio content is primarily spoken dialogue or narration.
By default, FFmpeg selects the first audio stream in the VOB file, which is typically the primary language track on a DVD. If your VOB contains multiple audio tracks — such as director's commentary, alternate language dubs, or descriptive audio — you'll need to specify the track explicitly using the '-map' flag on the command line, for example adding '-map 0:a:1' to select the second audio stream before the output filename.
VOB files are inherently large because they contain full MPEG-2 video (often at several Mbps), AC3 audio, subtitle streams, and DVD structural data. The AMR output discards all video and subtitle content entirely and encodes only the audio at 12200 bps — roughly 1.5 KB per second of audio. A 1-hour VOB that might be 4–6 GB will produce an AMR file of only around 5–6 MB, a reduction of roughly 99% or more in file size.
AMR-NB only supports eight fixed bitrate modes: 4750, 5150, 5900, 6700, 7400, 7950, 10200, and 12200 bps. The default used here — 12200 bps — is already the maximum for AMR Narrowband. If you need broader frequency response and better fidelity, you could instead use the AMR Wideband codec (libopencore_amrwb), which operates at 16 kHz and supports bitrates up to 23850 bps, by changing the codec flag in the command to '-c:a libopencore_amrwb'. AMR-WB will preserve more of the audio's original quality, though it is still optimized for speech.
To change the AMR bitrate, replace '12200' in the '-b:a 12200' flag with any of the supported AMR-NB values: 4750, 5150, 5900, 6700, 7400, 7950, or 10200. Lower bitrates produce smaller files with reduced intelligibility; 12200 is the maximum and best-sounding option for AMR-NB. To switch to AMR Wideband instead, replace '-c:a libopencore_amrnb' with '-c:a libopencore_amrwb' and use a supported AMR-WB bitrate such as 23850. Note that FFmpeg must be compiled with libopencore-amrnb and libopencore-amrwb support for these codecs to be available on your local desktop installation.
No. AMR is a bare audio-only format with no container structure capable of holding subtitles, chapter markers, or metadata beyond basic audio stream information. All DVD subtitle streams (VOB subtitles, closed captions) and any chapter data are discarded during conversion. If preserving subtitles or chapters matters, you would need to choose an output format that supports those features, such as MKV or MP4.
Technical Notes
The libopencore_amrnb encoder enforces strict constraints that significantly shape the output: it requires mono audio at exactly 8000 Hz, so FFmpeg automatically inserts a resampler and downmix filter to convert the VOB's AC3 track (commonly 48 kHz, stereo or 5.1 surround) down to the required format before encoding. This automatic channel and sample-rate conversion is lossy and irreversible — spatial audio information and high-frequency content above ~4 kHz are permanently discarded. The 12200 bps default corresponds to AMR-NB mode 7 (the 'MR122' mode), which is the highest quality mode and closest to standard telephone narrowband speech quality. VOB files sourced from dual-layer DVDs or VIDEO_TS folders may contain multiple VOB segments; if you need to process a full DVD title, you should first concatenate the VOB files (e.g., VTS_01_1.VOB, VTS_01_2.VOB) using FFmpeg's concat demuxer before running this conversion. Additionally, AC3 audio in VOBs sometimes carries Dolby Surround encoding — the downmix to mono may produce phase cancellation artifacts on some content, which is a known limitation of the narrowband target format rather than an FFmpeg bug.