MyMediaTools

Convert VOB to MKV — Free Online Tool

Convert VOB files from DVD discs into MKV format, re-encoding the MPEG-2 video to H.264 (libx264) and the AC3 audio to AAC — producing a modern, compact file that preserves subtitle streams and multiple audio tracks in Matroska's flexible open-standard container.

FFmpeg Command

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How It Works

VOB files store DVD content as MPEG-2 video (typically at constant bitrates of 4–9 Mbps) alongside AC3 (Dolby Digital) audio, DVD subtitles (bitmap-based VobSub streams), and sometimes multiple language tracks. During this conversion, the MPEG-2 video is fully re-encoded to H.264 using libx264's CRF mode, which trades the DVD's rigid CBR encoding for a more efficient variable-bitrate output — typically reducing file size by 50–70% at comparable perceptual quality. The AC3 audio is transcoded to AAC, which offers similar or better quality at lower bitrates. Subtitle streams and multiple audio tracks supported by the VOB container are carried over into the MKV container, which natively supports all of them. Because both the video and audio codecs change, this is a full transcode, not a remux.

What Each Flag Does

Flag What it does
ffmpeg Invokes the FFmpeg binary — the open-source multimedia processing engine that performs the actual VOB-to-MKV transcode, including MPEG-2 decoding, H.264 encoding, and AC3-to-AAC conversion.
-i input.vob Specifies the input VOB file. FFmpeg reads the multiplexed MPEG-2 video, AC3 audio, and any subtitle or metadata streams stored in this DVD Video Object container.
-c:v libx264 Re-encodes the MPEG-2 video stream from the VOB using libx264, the gold-standard H.264 encoder. This replaces the DVD's fixed-bitrate MPEG-2 with a far more efficient variable-bitrate H.264 stream, dramatically reducing file size while maintaining comparable visual quality.
-c:a aac Transcodes the AC3 (Dolby Digital) audio track from the DVD into AAC, which is broadly supported across modern devices and browsers. AAC replaces the DVD-native AC3 codec while maintaining similar audio quality at lower or equivalent bitrates.
-crf 23 Sets the Constant Rate Factor for the libx264 encoder to 23, the default quality level. For standard-definition DVD source material, this produces a good balance between file size reduction and perceptual fidelity — the output will be visibly close to the MPEG-2 source while being substantially smaller.
-b:a 128k Sets the AAC audio bitrate to 128 kilobits per second. For stereo audio — which is typical of DVD content after downmix — 128k AAC is generally considered transparent quality. If the source has 5.1 surround audio, consider increasing this to 192k or 256k to preserve more spatial detail.
output.mkv Defines the output file as an MKV (Matroska) container. The .mkv extension tells FFmpeg to wrap the H.264 video and AAC audio into the Matroska format, which supports chapters, multiple audio tracks, and subtitle streams — making it an ideal modern replacement for the VOB container.

Common Use Cases

  • Ripping a DVD and archiving its content as a smaller H.264 MKV file without losing the original subtitle tracks or alternate language audio streams
  • Preparing a DVD movie or concert video for playback on a media server like Jellyfin or Plex, which handles MKV/H.264 far more efficiently than raw MPEG-2 VOB files
  • Converting a home movie burned to DVD into a modern MKV file for long-term storage, reducing the multi-gigabyte VOB size to something more manageable
  • Editing DVD footage in a timeline-based editor that accepts MKV/H.264 but struggles with MPEG-2 VOB's interleaved structure and navigation data
  • Sharing a DVD-sourced recording online or via USB where MPEG-2 VOB playback compatibility is limited, but H.264 MKV plays natively on virtually every modern device
  • Converting VOB files from a DVD training course or lecture series into MKV for offline viewing on a laptop or tablet without a disc drive

Frequently Asked Questions

Yes — MKV natively supports subtitle streams, and FFmpeg will map them from the VOB file into the output MKV by default when they are detected. DVD subtitles are bitmap-based (VobSub format), and they are carried over as-is without re-rendering. If you want to explicitly include all subtitle streams, add '-c:s copy' and '-map 0' to the FFmpeg command.
Significantly smaller in most cases. DVD MPEG-2 video is encoded at fixed high bitrates (often 6–8 Mbps) regardless of scene complexity, while H.264 with CRF 23 adapts the bitrate to the content — typically producing files 50–70% smaller with comparable perceived quality. A 4GB VOB file might yield an MKV of 800MB–1.5GB depending on the source material's complexity and duration.
Yes — this is a lossy-to-lossy transcode. The MPEG-2 source is already lossy, and re-encoding to H.264 introduces a second generation of compression. However, at CRF 23, libx264 typically produces output that is perceptually very close to the source for standard-definition DVD content. If you want higher fidelity, lower the CRF value (e.g., '-crf 18') in the command at the cost of a larger file.
The AC3 audio is transcoded to AAC at 128k by default. AAC is not identical to AC3 — it uses a different psychoacoustic model — so this is a lossy re-encoding step. For most viewers the difference is inaudible at 128k, but if you are preserving a 5.1 surround AC3 track and want to keep it intact, you can replace '-c:a aac' with '-c:a copy' in the command to pass the original AC3 stream through unchanged into the MKV container, which supports it natively.
By default, FFmpeg selects one audio stream (usually the first). To include all audio tracks from the VOB, add '-map 0:v -map 0:a -map 0:s' to the command, or simply '-map 0' to copy every stream. Each audio track will be transcoded to AAC individually unless you use '-c:a copy' to preserve the original AC3 streams.
Adjust the '-crf' value. CRF (Constant Rate Factor) controls the quality-to-size tradeoff for libx264 — lower values mean higher quality and larger files, higher values mean smaller files with more compression. CRF 18 is considered visually near-lossless for DVD-resolution content, CRF 23 is the default, and CRF 28 produces noticeably smaller but softer output. For DVD source material, values between 18 and 23 are typically the sweet spot.

Technical Notes

VOB files are not always standalone — a full DVD title is often split across multiple VOB files (VTS_01_1.VOB, VTS_01_2.VOB, etc.) with a companion IFO navigation file. This tool processes a single VOB file at a time; if you need to concatenate multiple VOBs before converting, the desktop FFmpeg command supports concatenation via the concat demuxer. The MPEG-2 video inside a VOB is interlaced in many DVD productions, particularly older films and broadcast content. FFmpeg will not automatically deinterlace; for cleaner output from interlaced sources, add '-vf yadif' to the command. DVD subtitles (VobSub) are bitmap-image based rather than text-based, so they cannot be searched or restyled in the MKV output without an OCR step. Chapter markers present in the DVD's IFO file are not embedded in VOB files themselves and will not appear in the MKV output. The MKV container fully supports H.264, AAC, AC3, and VobSub, making it an ideal archival destination for DVD content with no container-level feature loss.

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