MyMediaTools

Compress VOB Online — Free File Size Reducer

Compress VOB files by re-encoding with MPEG-2 video and AC3 audio at lower quality settings, reducing DVD-rip file sizes while preserving the VOB container structure, subtitle streams, and multiple audio tracks compatible with DVD players and media servers.

FFmpeg Command

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How It Works

Unlike a simple remux, this tool fully re-encodes both the MPEG-2 video stream and the AC3 audio stream within the VOB container. The video is re-encoded using the MPEG-2 codec at a higher quantizer scale value (q:v 4 by default), which reduces bitrate and file size at the cost of some visual quality compared to the original. The AC3 audio is re-encoded at 192k — a significant reduction from the 384k–448k bitrates commonly found on pressed DVDs. The output retains the VOB container with the -f vob flag, preserving compatibility with DVD playback software and hardware, as well as subtitle stream passthrough.

What Each Flag Does

Flag What it does
ffmpeg Invokes the FFmpeg tool, which is running here as a WebAssembly (FFmpeg.wasm) instance entirely inside your browser — no data is sent to any server.
-i input.vob Specifies the input VOB file. FFmpeg reads the MPEG Program Stream structure of the VOB, detecting the embedded MPEG-2 video and AC3 audio elementary streams for re-encoding.
-c:v mpeg2video Sets the video encoder to MPEG-2, re-encoding the video stream using the same codec as the source. This is required for DVD-Video compatibility — the VOB container does not support modern codecs like H.264.
-q:v 4 Sets the MPEG-2 video quantizer scale to 4 on a range of 1 (highest quality) to 31 (most compressed). A value of 4 targets good visual quality with meaningful file size reduction compared to the high-bitrate video tracks on pressed DVDs.
-c:a ac3 Re-encodes the audio stream using the AC3 (Dolby Digital) codec, which is the standard audio format required for DVD-Video compatibility and is the native audio format in the original VOB.
-b:a 192k Sets the AC3 audio bitrate to 192 kilobits per second. This is lower than the 384k–448k typically used on commercial DVDs, reducing audio file size while maintaining acceptable stereo quality for most content.
-f vob Forces the output container format to VOB (DVD MPEG Program Stream). Without this flag, FFmpeg might not correctly mux the output as a valid VOB file, which is required for DVD player and media server compatibility.
output.vob The filename of the compressed output VOB file. The .vob extension combined with the -f vob flag ensures the result is a valid DVD-Video Object file that can be played by hardware DVD players, VLC, Kodi, and other compatible software.

Common Use Cases

  • Reducing the size of ripped DVD VOB files to fit more content on a NAS or media server without changing container format
  • Archiving old DVD collections at smaller file sizes when storage space is limited and perfect quality is not required
  • Preparing VOB files for playback on older hardware DVD players or set-top boxes that only accept MPEG-2/AC3 streams in a VOB container
  • Trimming down large multi-angle or bonus-feature VOB files that contain AC3 audio at high bitrates you want to reduce
  • Creating lower-bitrate preview or reference copies of DVD content for editorial review without converting to a different format
  • Compressing VOB files from camcorder DVDs where the original recording is oversized for sharing or archiving

Frequently Asked Questions

Yes, because this tool re-encodes the MPEG-2 video stream rather than copying it, each re-encode introduces additional compression artifacts compared to the original DVD source. The default q:v 4 setting preserves reasonably good quality, but VOB files from pressed DVDs typically use higher bitrates than what re-encoding at this setting produces. If you need minimal quality loss, use a lower q:v value (e.g., 1 or 2), though this will result in larger output files.
This specific tool is designed for VOB-to-VOB compression, meaning you want to reduce file size while keeping the DVD-compatible container format intact. VOB is required for compatibility with DVD players, set-top boxes, and software that expects MPEG-2 video and AC3 audio in a DVD container structure. If you need to convert VOB to MP4 or MKV, a different tool on this site handles that conversion.
Subtitle streams (DVD bitmap subtitles encoded as MPEG-2 private streams) are supported by the VOB container, but whether they are carried through depends on the FFmpeg command configuration. The base command shown here focuses on video and audio re-encoding; to explicitly copy subtitle streams, you would add -c:s copy to the command when running it locally. The tool preserves the container's subtitle capability, but complex multi-stream VOB structures from commercial DVDs may require manual stream mapping.
File size reduction depends heavily on the original VOB's bitrate. DVD-Video typically uses 4–8 Mbps for MPEG-2 video and 384k–448k for AC3 audio, while this tool's defaults target a lower quantizer (q:v 4) and 192k AC3. You can expect roughly 30–60% size reduction for typical DVD rips, though the exact result varies by content complexity. High-motion content like action films compresses less efficiently than slow-paced documentaries under MPEG-2 encoding.
The -q:v flag controls MPEG-2 video quality on a scale of 1 (best quality, largest file) to 31 (worst quality, smallest file). The default is 4, which balances quality and size well for most DVD content. To increase compression, raise the value — for example, replacing -q:v 4 with -q:v 8 or -q:v 12 will significantly reduce file size at the expense of visible blocking artifacts in complex scenes. You can also reduce audio size by lowering -b:a, for example changing 192k to 128k, though AC3 at 128k may sound noticeably degraded on surround content.
Yes, when running the command locally you can use a shell loop to process multiple files. On Linux or macOS, use: for f in *.vob; do ffmpeg -i "$f" -c:v mpeg2video -q:v 4 -c:a ac3 -b:a 192k -f vob "compressed_$f"; done. On Windows Command Prompt, use a for loop with %f. This is one of the main advantages of having the exact FFmpeg command — the browser-based tool processes one file at a time, but the command line version handles batch jobs efficiently for large DVD archives.

Technical Notes

VOB files are MPEG Program Stream containers with a DVD-specific structure defined by the DVD-Video specification. Re-encoding within the VOB format requires both the -f vob flag to force the correct container muxer and codecs restricted to what the DVD spec allows — primarily MPEG-2 video and AC3 (Dolby Digital) audio. The q:v parameter for MPEG-2 is a quantizer scale rather than a CRF value (as used in H.264/H.265), meaning quality and bitrate vary by scene complexity rather than being fixed. One important limitation is that commercial DVD VOB files often contain multiple program chains, angle blocks, and copy-protection structures (CSS) that FFmpeg cannot replicate in output — this tool is best suited for already-ripped, unencrypted VOB files. AC3 re-encoding at 192k produces stereo-compatible output but may reduce the perceived surround sound quality of 5.1 original tracks encoded at 448k; for surround preservation, increase -b:a to 384k or 448k. Chapter markers are not supported in the VOB output from FFmpeg, so chapter data from the original IFO/VOB structure will not be retained.

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