MyMediaTools

Convert VOB to WebM — Free Online Tool

Convert VOB files from DVD-Video discs to WebM format, re-encoding the MPEG-2 video stream with VP9 and the AC3 audio with Opus — producing a compact, web-native file that plays directly in modern browsers without plugins. This is ideal for archiving DVD content in an open, royalty-free format optimized for online sharing and HTML5 video embedding.

FFmpeg Command

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Estimated output:

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How It Works

VOB files contain MPEG-2 video and AC3 (Dolby Digital) audio multiplexed together in a DVD-specific container. Because WebM only supports VP9 (or VP8) video and Opus/Vorbis audio, this conversion requires full re-encoding of both streams — no stream copying is possible. The MPEG-2 video is decoded frame-by-frame and re-encoded using the VP9 codec in constant-quality mode (CRF), which produces a significantly smaller file than the original MPEG-2 stream while often matching or exceeding its visual quality. The AC3 audio is decoded and re-encoded as Opus, a modern codec that delivers excellent quality at lower bitrates than AC3. The resulting WebM file is wrapped in a Matroska-based container that supports chapters, subtitles, and multiple audio tracks — features also present in VOB, though subtitle streams from VOB (typically bitmap-based DVD subtitles) require separate handling and are not automatically carried over in this conversion.

What Each Flag Does

Flag What it does
ffmpeg Invokes the FFmpeg program. In the browser-based version of this tool, this runs via FFmpeg.wasm compiled to WebAssembly — no files leave your device. On the desktop, this requires FFmpeg to be installed and accessible in your system PATH.
-i input.vob Specifies the input VOB file. FFmpeg automatically detects the MPEG-2 Program Stream container and identifies the MPEG-2 video and AC3 audio streams inside it, even though the .vob extension is DVD-specific.
-c:v libvpx-vp9 Selects the VP9 video encoder, which is the only video codec supported by the WebM container. This re-encodes the MPEG-2 video from the VOB from scratch — there is no way to copy MPEG-2 into a WebM file.
-c:a libopus Selects the Opus audio encoder to replace the AC3 (Dolby Digital) audio from the VOB file. Opus is the preferred audio codec for WebM and delivers better quality than AC3 at lower bitrates, making it well-suited for web delivery.
-crf 33 Sets the VP9 constant-quality level to 33 on a scale of 0 (lossless) to 63 (lowest quality). A value of 33 is a balanced default for DVD-quality source material; lower values like 24 or 28 will produce sharper output at the cost of a larger WebM file.
-b:a 128k Sets the Opus audio bitrate to 128 kilobits per second. Opus is highly efficient at this bitrate and will sound transparent for most stereo content, though if the source VOB contains a 5.1 surround AC3 track, increasing this to 256k is recommended to better preserve the extra channels.
-b:v 0 This flag is required alongside -crf when encoding VP9 — it explicitly disables average-bitrate mode and tells the encoder to use pure constant-quality mode driven entirely by the CRF value. Without this flag, VP9 may ignore the CRF setting and produce inconsistent quality.
output.webm Specifies the output filename and tells FFmpeg to wrap the VP9 video and Opus audio in a WebM container. The .webm extension triggers automatic container selection, producing a file that plays natively in Chrome, Firefox, Edge, and other modern browsers without any plugins.

Common Use Cases

  • Ripping a DVD movie or home video and converting it to WebM for embedding directly in an HTML5 <video> tag on a website without relying on proprietary formats
  • Archiving a personal DVD collection in an open, royalty-free format that does not depend on licensed MPEG-2 or Dolby Digital decoders for playback
  • Preparing DVD lecture recordings or training videos for upload to a web platform or intranet that requires WebM for bandwidth-efficient streaming
  • Converting VOB files from a camcorder or DVD recorder to a smaller WebM file for sharing via a web link, where MPEG-2 playback support on the recipient's device is uncertain
  • Reducing the file size of large VOB recordings (DVD-quality MPEG-2 is bitrate-heavy) by leveraging VP9's superior compression efficiency for long-term storage
  • Converting DVD-sourced video content to WebM for use in a Chromium-based kiosk or web app where native HTML5 WebM playback is guaranteed

Frequently Asked Questions

Some generation loss is unavoidable because this conversion re-encodes the MPEG-2 video rather than copying it — WebM cannot contain MPEG-2 streams. However, VP9 is a significantly more efficient codec than MPEG-2, so at a comparable file size the VP9 output can actually look sharper, especially in motion-heavy scenes where MPEG-2 blocking artifacts are common. Using the default CRF 33 setting produces a visually good result for most DVD-quality (480p/576i) content; lowering the CRF value (e.g., to 24 or 20) increases quality at the cost of a larger file.
The AC3 audio track is fully decoded and re-encoded as Opus at 128k by default. Opus is a modern, royalty-free codec that generally outperforms AC3 at equivalent or lower bitrates, particularly for speech-heavy content. However, if your VOB contains a 5.1 surround AC3 track, Opus at 128k will downmix and compress it — consider raising the audio bitrate to 256k or higher with -b:a 256k to better preserve multi-channel audio fidelity.
DVD subtitles in VOB files are stored as bitmap image streams (DVD subtitles, also called VobSub), not as text. WebM supports WebVTT text subtitles, but bitmap subtitle streams cannot be directly copied into a WebM container. To include subtitles, you would need to either burn them into the video with a filter (-vf subtitles) or use a separate tool to OCR the VobSub images into a text-based format first. This conversion does not automatically transfer DVD subtitle streams.
The -crf 33 flag controls VP9 quality on a scale from 0 (lossless) to 63 (lowest quality). Lower values mean higher quality and larger files. For DVD-sourced 480p/576i content, a CRF between 24 and 33 is typically the sweet spot — try -crf 28 for noticeably better detail without a dramatic file size increase. Always keep -b:v 0 in the command alongside -crf, as VP9 requires this flag to enable true constant-quality mode rather than average-bitrate mode.
Yes. On Linux or macOS, you can loop over all VOB files in a directory with: for f in *.vob; do ffmpeg -i "$f" -c:v libvpx-vp9 -c:a libopus -crf 33 -b:a 128k -b:v 0 "${f%.vob}.webm"; done. On Windows Command Prompt, use: for %f in (*.vob) do ffmpeg -i "%f" -c:v libvpx-vp9 -c:a libopus -crf 33 -b:a 128k -b:v 0 "%~nf.webm". Note that VP9 encoding is computationally slow, so batch processing large VOB files will take significant time.
MPEG-2 was designed in the early 1990s for real-time hardware encoding on dedicated DVD authoring equipment. VP9 is a far more computationally complex codec that achieves better compression through advanced techniques like larger block sizes, recursive partitioning, and more sophisticated motion estimation — all of which require significant CPU work during encoding. You can speed up VP9 encoding by adding -speed 4 (or up to 8) to the command at the cost of slightly reduced compression efficiency, which is useful when processing many VOB files from a DVD collection.

Technical Notes

VOB files are essentially MPEG-2 Program Stream containers with a DVD-specific extension, and they frequently arrive as a series of 1GB-split files (VTS_01_1.VOB, VTS_01_2.VOB, etc.) from a DVD rip. If you need to convert an entire DVD title spread across multiple VOB files, you should concatenate them first using FFmpeg's concat demuxer before applying this conversion. The default VP9 encoding in this command uses CRF mode with -b:v 0, which is the recommended approach for quality-driven encoding — omitting -b:v 0 would switch VP9 to a different rate control mode and produce unpredictable quality. VOB files often contain interlaced video (typical of PAL and NTSC DVD standards), and VP9 encodes in progressive mode; for best results with interlaced source material, add a deinterlacing filter such as -vf yadif before encoding. Audio quality in WebM is generally excellent with Opus even at 128k, but original AC3 bitrates on DVDs commonly range from 192k to 448k, so audiophiles converting high-quality DVD audio may want to raise -b:a to 192k or 256k. The WebM output supports chapters and multiple audio tracks at the container level, but multiple audio tracks from a VOB must be explicitly mapped with -map flags to be included.

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