DVD Video Object
VOB is the primary video container on DVD-Video discs, holding MPEG-2 video, AC-3 or DTS audio, and bitmap subtitles. FileDex converts VOB to MP4 directly in your browser using FFmpeg WASM — no upload required.
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Common questions
How do I inspect the contents of a VOB file?
Use ffprobe -show_streams input.vob to list all video, audio, and subtitle tracks. VLC (Media > Codec Information) also displays stream details. VOB files often contain multiple audio tracks in different languages.
Why are VOB files limited to 1 GB?
The DVD-Video specification uses the UDF filesystem, which imposes a 1 GB file size limit per VOB. Longer titles are split across multiple files (VTS_01_1.VOB through VTS_01_9.VOB) that play sequentially.
Can I convert VOB to MP4 without losing quality?
No — VOB uses MPEG-2 video and converting to MP4 (H.264) requires re-encoding, which is lossy. However, at CRF 18-20 the quality difference is imperceptible while file size drops by 50-70%. For lossless preservation, remux to MKV instead.
How do I merge multiple VOB files into one video?
Use ffmpeg with the concat protocol: create a text file listing each VOB, then run ffmpeg -f concat -i list.txt -c copy output.mkv. This preserves quality and handles the DVD file splitting transparently.
What makes .VOB special
DVD Video Object files are the core media containers of the DVD-Video specification, holding multiplexed MPEG-2 video, audio, subtitles, and navigation data in a structure defined by the DVD Forum's specification from 1996. Each VOB is technically an MPEG Program Stream with DVD-specific extensions for menus, multi-angle video, and region coding. The 1 GB file size limit per VOB comes from the UDF filesystem specification used on DVDs — a 2-hour movie is typically split across 4-6 files named VTS_01_1.VOB through VTS_01_6.VOB, with the player seamlessly chaining them during playback.
Continue reading — full technical deep dive
File structure on disc
A DVD's VIDEO_TS directory contains three file types:
| File pattern | Purpose |
|---|---|
| VIDEO_TS.VOB | First-play menu and root navigation |
| VTS_xx_0.VOB | Title set menu for title xx |
| VTS_xx_1.VOB through VTS_xx_9.VOB | Actual movie content for title xx |
| VTS_xx_0.IFO / .BUP | Navigation index and backup |
The .IFO files contain the Program Chain (PGC) tables that control playback order, chapter points, and prohibited user operations (like skipping FBI warnings). Without the .IFO, a VOB file plays but loses chapter markers, menu navigation, and audio/subtitle stream selection metadata.
Codec constraints
DVD-Video mandates specific codec and resolution combinations:
- Video: MPEG-2 Part 2 at 720x480 (NTSC) or 720x576 (PAL), maximum 9.8 Mbps
- Audio: AC-3 (Dolby Digital) up to 448 kbps, MPEG-1 Layer II, LPCM at 1536 kbps, or DTS at 1536 kbps
- Subtitles: Bitmap-based subpictures rendered as overlays, not text
The combined bitrate of all streams cannot exceed 10.08 Mbps — the maximum read speed of a 1x DVD drive. Most commercial DVDs target 6-8 Mbps total to leave headroom for layer changes and error correction.
Subtitles in VOB files are bitmapped images, not text. Each subtitle is a small RLE-compressed image with a 4-color palette. This design choice from 1996 meant studios could use any font and avoid text rendering bugs across players, but it makes subtitle extraction require OCR to produce editable text.
CSS encryption and ripping
Most commercial VOBs are encrypted with CSS (Content Scramble System), a 40-bit key encryption scheme that was famously broken in 1999 by DeCSS. The encryption works per-sector, with title keys stored in the .IFO files and a disc key accessible only through a licensed drive's authentication handshake. Raw VOB files ripped without decryption contain scrambled sectors that produce garbled video and audio.
Performance characteristics
A single-layer DVD holds 4.7 GB, a dual-layer disc 8.5 GB. At maximum video bitrate (9.8 Mbps), a single-layer disc stores roughly 60 minutes of video. Most feature films use dual-layer discs with variable bitrate encoding averaging 5-6 Mbps, yielding 120-150 minutes of content.
VOB muxing overhead is minimal — Program Stream headers add less than 1% to the total file size. The real space cost is the mandatory AC-3 audio track (typically 192-448 kbps) plus any additional language tracks and director commentaries.
Converting VOB files
FileDex handles VOB-to-MP4 conversion in the browser by demuxing the MPEG-2 Program Stream and re-encoding the video to H.264. Expect processing speeds of 2-5x realtime on a modern machine, since MPEG-2 decode is computationally light but H.264 encode carries the usual cost. Audio streams can be passed through if the target container supports AC-3, or transcoded to AAC for broader compatibility.
When VOB still appears
DVD rips remain the primary source of VOB files today. Legacy media archives, library digitization projects, and personal DVD collections generate millions of VOB files annually. The format is frozen — no new features will ever be added. For archival purposes, converting to MKV preserves all streams (including subtitle bitmaps and multiple audio tracks) without quality loss through simple remuxing.
.VOB compared to alternatives
| Formats | Criteria | Winner |
|---|---|---|
| .VOB vs .MP4 | Compatibility and file size MP4 with H.264 plays natively on every modern device and browser. VOB requires DVD player software and produces files 3-5x larger than equivalent MP4 due to MPEG-2 compression inefficiency. | MP4 wins |
| .VOB vs .MKV | Archival and feature support MKV supports lossless remuxing of VOB content with chapter markers, multiple audio tracks, and subtitle streams. VOB is limited to the DVD specification constraints including 1 GB file size cap. | MKV wins |
| .VOB vs .AVI | Container flexibility VOB supports multiple audio tracks, subtitle streams, and DVD navigation data. AVI lacks native subtitle support and has limited multi-track audio capabilities. | VOB wins |
Convert .VOB to...
Technical reference
- MIME Type
video/dvd- Magic Bytes
00 00 01 BAMPEG Program Stream pack header.- Developer
- DVD Forum
- Year Introduced
- 1996
- Open Standard
- No
MPEG Program Stream pack header.
Binary Structure
VOB files are MPEG-2 Program Stream containers beginning with a pack header at offset 0x00. The 4-byte pack start code 00 00 01 BA is followed by 2 bits (01) identifying MPEG-2, then a 3-part system clock reference (SCR) encoded across 6 bytes with marker bits, and a 22-bit mux rate field. Packs contain one or more PES (Packetized Elementary Stream) packets, each starting with the 3-byte prefix 00 00 01 followed by a stream ID byte: 0xE0 for video, 0xBD for private stream 1 (AC-3, DTS, or subtitle data), 0xC0-0xDF for MPEG audio. Each PES header carries a 2-byte packet length, flags for PTS/DTS timestamps (33-bit, 90 kHz clock), and optional stuffing bytes. DVD-specific extensions use the private stream 1 sub-stream ID: first byte after the PES header payload identifies the sub-stream (0x80-0x87 for AC-3, 0x88-0x8F for DTS, 0xA0-0xA7 for LPCM, 0x20-0x3F for subtitles). Navigation packs (NAV packs) contain PCI and DSI packets for menu and chapter control. VOB files on disc are limited to 1 GB each; larger titles span VTS_01_1.VOB through VTS_01_9.VOB.
| Offset | Length | Field | Example | Description |
|---|---|---|---|---|
0x00 | 4 bytes | Pack start code | 00 00 01 BA | MPEG-2 Program Stream pack start code. Identifies the beginning of a pack. |
0x04 | 6 bytes | SCR + mux rate | 44 00 04 00 04 01 | System Clock Reference (33-bit + 9-bit extension) and 22-bit mux rate with marker bits. |
0x0D | 1 byte | Pack stuffing length | F8 | Low 3 bits indicate stuffing byte count (0-7). Upper 5 bits are reserved (set to 1). |
PES offset | 4 bytes | PES start code + stream ID | 00 00 01 E0 | 00 00 01 prefix followed by stream ID: 0xE0=video, 0xBD=private (AC-3/DTS/subs), 0xC0=MPEG audio. |
PES + 0x04 | 2 bytes | PES packet length | 07 EC | Length of the PES packet data following this field. 0x0000 signals unbounded video PES. |
PES + 0x06 | 3+ bytes | PES header flags + optional fields | 81 80 05 | Flags indicate PTS/DTS presence, ESCR, ES rate, trick mode. Followed by timestamps and stuffing. |
Attack Vectors
- Malformed MPEG-2 PES packets can trigger buffer overflows in outdated demuxer libraries
- CSS decryption tools may bundle adware or malware in unofficial distributions
Mitigation: FileDex processes files locally using FFmpeg WASM in a sandboxed browser environment.