MyMediaTools

Convert VOB to MP4 — Free Online Tool

Convert VOB files from DVD-Video discs into MP4, re-encoding the MPEG-2 video stream to H.264 (libx264) and the AC3 audio to AAC — producing a compact, universally playable file that works on phones, browsers, and streaming platforms without requiring a DVD drive.

FFmpeg Command

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How It Works

VOB files store DVD content as multiplexed MPEG-2 video and AC3 (Dolby Digital) audio, a format that modern devices rarely play natively. This conversion fully re-encodes both streams: the MPEG-2 video is decoded and re-encoded to H.264 using libx264 with a CRF of 23, which typically cuts file size dramatically while maintaining visually similar quality. The AC3 audio is decoded and re-encoded to AAC at 128k, which is broadly supported across all MP4-compatible players. The -movflags +faststart flag reorganizes the MP4 metadata to the front of the file, enabling progressive playback in browsers and streaming apps before the file is fully downloaded. Because MPEG-2 is an older, less efficient codec, the resulting H.264 MP4 is usually 40–70% smaller than the original VOB at comparable visual quality.

What Each Flag Does

Flag What it does
ffmpeg Invokes the FFmpeg tool, which handles all demuxing, decoding, encoding, and muxing for this VOB-to-MP4 conversion pipeline.
-i input.vob Specifies the input VOB file. FFmpeg automatically identifies the MPEG-2 Program Stream container and detects the MPEG-2 video and AC3 audio streams inside the DVD structure.
-c:v libx264 Re-encodes the MPEG-2 video stream from the VOB to H.264 using the libx264 encoder, which is far more compression-efficient than MPEG-2 and universally supported in MP4 players, browsers, and mobile devices.
-c:a aac Re-encodes the AC3 (Dolby Digital) audio from the VOB to AAC, the standard audio codec for MP4 files. This ensures the output plays on devices that support MP4 but do not natively decode AC3.
-crf 23 Sets the Constant Rate Factor for libx264 to 23, the default quality level. Lower values (e.g., 18) produce higher quality and larger files; higher values (e.g., 28) produce smaller files with more compression — calibrated here for a good balance given DVD's 480p source resolution.
-b:a 128k Sets the AAC audio bitrate to 128 kilobits per second. This is appropriate for stereo output from a downmixed DVD AC3 track and is the standard quality level for web-compatible MP4 audio.
-movflags +faststart Moves the MP4 MOOV atom (metadata index) to the beginning of the output file, enabling the video to begin playing in a browser or streaming app before the entire file has been downloaded — a critical step for any web-delivered MP4 converted from a DVD source.
output.mp4 Specifies the output filename. The .mp4 extension tells FFmpeg to mux the re-encoded H.264 video and AAC audio into an MPEG-4 Part 14 container, replacing the original VOB's DVD-specific Program Stream structure.

Common Use Cases

  • Ripping a home movie DVD into a portable MP4 you can play on a smartphone, tablet, or smart TV without needing a disc drive
  • Archiving a DVD collection to a NAS or media server like Plex or Jellyfin, which require H.264 MP4 for direct-play without transcoding overhead
  • Uploading a DVD-sourced video to YouTube, Vimeo, or another platform that accepts MP4 but does not support raw VOB files
  • Editing DVD footage in video editing software (e.g., DaVinci Resolve, Premiere Pro) that handles H.264 MP4 far better than MPEG-2 VOB
  • Sending a DVD recording of a family event to relatives who only have devices capable of playing standard MP4 files
  • Reducing storage footprint of large VOB files from dual-layer DVDs (up to 8.5 GB) into a single, smaller MP4 without perceptible quality loss

Frequently Asked Questions

Some quality loss is unavoidable because this conversion re-encodes MPEG-2 video to H.264 — a lossy-to-lossy transcode. However, the default CRF 23 setting for libx264 is specifically tuned to be visually transparent for most content, and standard DVD video is only 480i/480p resolution, so the difference is rarely visible on modern screens. The real benefit is that H.264 at the same perceptual quality is far more efficient than MPEG-2, so file sizes drop significantly. If quality is critical, you can lower the CRF value (e.g., to 18) in the FFmpeg command for a closer match to the source at the cost of a larger file.
MPEG-2, the video codec used in DVDs, was designed in the early 1990s and is much less compression-efficient than H.264. H.264 (libx264) uses advanced prediction and entropy coding techniques that can store the same visual information using far fewer bits. A typical 1-hour VOB at ~4 GB can often be re-encoded to an H.264 MP4 under 1 GB at CRF 23 with no visible degradation. The switch from AC3 to AAC audio also contributes modest additional savings.
The AC3 audio track is decoded and re-encoded to AAC at 128k stereo by default. This means any 5.1 surround sound in the original DVD will be downmixed to stereo during conversion. If you need to preserve the full AC3 surround track — for example, for a home theater setup — you can modify the command to use -c:a copy if your MP4 player supports AC3, or use -b:a 320k with AAC to improve stereo fidelity. Note that MP4 containers do support AC3 audio, but not all players handle it reliably.
DVD titles are often split across multiple VOB files (each capped at 1 GB). You can use FFmpeg's concat demuxer to join them before or during conversion. Replace the input with a concat file listing all VOB parts in order: create a text file with lines like 'file VTS_01_1.VOB', 'file VTS_01_2.VOB', then run ffmpeg with -f concat -safe 0 -i filelist.txt in place of the single input. This processes the entire title as one continuous stream without re-encoding the segments separately.
Yes. To improve quality, lower the CRF value — for example, replace -crf 23 with -crf 18 for near-lossless H.264 output (at a larger file size). To increase compression for smaller files, raise it to -crf 28 or higher. Since DVD source material is 480i or 480p, you may also want to upscale it by adding -vf scale=1280:720 for a 720p output, though this does not recover detail that was never in the source. For audio, replace -b:a 128k with -b:a 192k or -b:a 256k if the source has a dense surround mix being downmixed to stereo.
DVD subtitle tracks (stored as bitmap-based VOBSUB streams) are not carried over by the default command. MP4 supports text-based subtitle tracks but VOBSUB bitmaps require explicit handling. To include subtitles, you would need to add -c:s mov_text for text subtitles or handle VOBSUB conversion separately using tools like SubRip. The default command focuses on the primary video and audio streams to ensure maximum compatibility of the output MP4.

Technical Notes

VOB files are a strict MPEG-2 Program Stream variant defined by the DVD-Video specification, meaning they always carry MPEG-2 (or occasionally MPEG-1) video and AC3, MPEG audio, or DTS audio. FFmpeg requires the -f vob flag to correctly identify the container when the file extension is ambiguous, but for standard .vob files the demuxer is detected automatically. The output H.264 stream uses libx264 in its default configuration, which targets the High profile at level 4.0 — compatible with virtually all devices manufactured after 2010. The -movflags +faststart flag performs a second pass to move the MOOV atom to the beginning of the MP4 file, which is essential for web embedding or streaming scenarios. One known limitation is that this tool processes a single VOB file at a time; multi-file DVD structures require concatenation before processing. Also note that VOB files from commercially pressed DVDs are typically CSS-encrypted, which FFmpeg cannot decrypt — this tool is intended for unencrypted VOB files such as those from home recordings, camcorder DVDs, or previously decrypted backups.

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