DVD-Video

DVD-Video is a disc format: a physical medium, a filesystem, a set of navigation tables, and a stream layout. It is the ancestor of the HD DVD Standard Content model, which reuses its Video Manager, Video Title Set, Program Chain, cell and navigation-pack structures at higher bit rates. This page documents the DVD-Video format itself, then the copy-protection mechanisms associated with DVD media.

Physical and logical basics

A DVD is a 120 mm disc (an 80 mm variant exists), 1.2 mm thick, built from two 0.6 mm substrates bonded together. It is read with a 650 nm laser. Data is organized in 2048-byte logical sectors; on disc, 16 sectors are grouped into one 32 KB ECC block protected by a Reed-Solomon product code. Each sector is carried as a 2064-byte data frame: a 12-byte header, 2048 bytes of main data, and a 4-byte error-detection code.

Disc types

Type	Sides	Layers per side	Nominal capacity
DVD-5	1	1	4.7 GB
DVD-9	1	2	8.5 GB
DVD-10	2	1	9.4 GB
DVD-18	2	2	17 GB

Capacities are in decimal gigabytes. Double-sided discs (DVD-10, DVD-18) are read by flipping the disc over; each side is an independent volume.

Dual-layer track paths

A dual-layer side can be laid out in one of two ways:

• PTP (Parallel Track Path) — both layers are read from the inside of the disc to the outside. The second layer’s addresses restart at the inside. Used for discs whose layers hold independent content.
• OTP (Opposite Track Path) — the first layer is read inside to outside, then the pickup refocuses on the second layer and reads it outside to inside. The two layers form one continuous address space, and the point where reading switches layers is the layer break. DVD-Video dual-layer movie discs use OTP.

Filesystem

DVD-Video uses the UDF 1.02 filesystem, with an ISO 9660 structure written alongside it as a bridge so that older readers can still see the files. The disc root contains two directories:

/  (UDF 1.02 + ISO 9660, 2048-byte sectors)
├── VIDEO_TS/    The DVD-Video content (.IFO .BUP .VOB)
└── AUDIO_TS/    Reserved for DVD-Audio; empty on a DVD-Video disc

The files in VIDEO_TS are stored contiguously, and the format caps each file at 1 GiB, which is why title content is split across several VOB files as described below.

Edge cases in the UDF structures

• A single UDF allocation descriptor carries a 30-bit length, so one extent covers at most 2^30 − 2048 bytes (0x3FFFF800, a whole number of sectors). A file of the full 1 GiB is therefore described by two or more consecutive descriptors.
• The top two bits of the same length field give the extent type: 0 = recorded and allocated, 1 = allocated but not recorded, 2 = neither, 3 = continuation of the descriptor list. A file’s first descriptor can be type 1: its address is where space is reserved, not where data lives, and the extent reads as zeros. The hole occupies logical file offsets; subsequent recorded extents must not be shifted down over it. An IFO with a leading hole does not have a valid header at file offset zero. Resolve file offsets through the allocation descriptors before deriving disc addresses.
• UDF 1.02 describes files and directories with a File Entry (descriptor tag 261: extended attribute length at byte 168, allocation descriptors from byte 176 plus that length). The Extended File Entry (tag 266: lengths at byte 208, descriptors from byte 216) belongs to later UDF revisions.
• The Main Volume Descriptor Sequence is located through the Anchor Volume Descriptor Pointer at sector 256, not at a fixed sector number.
• A UDF directory lists its files in the order the authoring tool wrote them, not in playback order. Playback order of the title VOBs is the order of their numbers _1 to _9.

VIDEO_TS structure

A disc consists of one Video Manager (VMG) and from 1 to 99 Video Title Sets (VTS). The VMG holds disc-level information and the top-level menus. Each VTS holds a group of titles that share a common set of attributes (video format, audio and subpicture stream layout) plus that group’s own menus.

File	Role
VIDEO_TS.IFO	Video Manager Information (VMGI) — disc-level control tables
VIDEO_TS.BUP	Backup copy of VIDEO_TS.IFO
VIDEO_TS.VOB	Video Manager menu objects (disc-level menus)
VTS_nn_0.IFO	Video Title Set Information (VTSI) for title set nn (01–99)
VTS_nn_0.BUP	Backup copy of VTS_nn_0.IFO
VTS_nn_0.VOB	Menu objects for title set nn
VTS_nn_1.VOB … VTS_nn_9.VOB	Title objects for title set nn

A VOB (Video Object) is an MPEG-2 Program Stream. The title VOBs of one VTS are logically one continuous stream that is divided into files of at most 1 GiB each, up to nine files (_1 through _9); the files are concatenated in numeric order. A BUP file is a byte-for-byte copy of the matching IFO, kept so that a damaged IFO can be recovered.

IFO structures

An IFO contains top-level tables located by sector pointers and nested structures located by byte offsets. Not every structure starts on a sector boundary; the First Play PGC, for example, has a byte-addressed pointer. The first sector holds a management table that begins with a 12-byte identifier — DVDVIDEO-VMG for VIDEO_TS.IFO, DVDVIDEO-VTS for a VTS_nn_0.IFO — followed by the specification version, attributes, and the sector pointers that locate every other table in the file. Pointers to tables are expressed in sectors relative to the start of the IFO file; the addresses inside tables that refer to VOB data are expressed in sectors relative to the start of the VOB set.

Video Manager Information (VMGI)

Table	Contents
VMGI_MAT	Management table: identifier, version, region mask, number of VTSs, pointers to every other table, the First Play PGC, and the VMG menu video, audio and subpicture attributes
TT_SRPT	Title search pointer table: one entry per title (see below)
VMGM_PGCI_UT	Menu PGC information, organized by menu language
PTL_MAIT	Parental management information table
VTS_ATRT	Attributes of every VTS on the disc, so that the VMG can know a title set’s video and stream layout without opening its IFO
TXTDT_MG	Text data manager (disc, title and chapter names; see Text data)
VMGM_C_ADT	Cell address table for the VMG menu VOB
VMGM_VOBU_ADMAP	VOBU address map for the VMG menu VOB

The TT_SRPT holds one 12-byte entry per title, up to 99 titles per disc. Each entry records the title type (including how the title may be entered and whether it has multiple angles), the number of angles, the number of chapters (PTTs), the parental ID mask, the VTS number the title lives in, the title number within that VTS (VTS_TTN), and the start sector of that VTS. Its layout:

Offset	Size	Field
0x00	2	Number of titles (at most 99)
0x08	12 each	Title entries, in disc title order (title 1 first)

Entry offset	Size	Field
+2	2	Number of chapters (PTTs) in the title
+6	1	VTS number (1-based)
+7	1	Title number within that VTS, VTS_TTN (1-based)

Two entries with the same VTS number and VTS_TTN resolve to the same content.

Video Title Set Information (VTSI)

Table	Contents
VTSI_MAT	Management table: identifier, version, pointers to every other table, and the video, audio (up to 8) and subpicture (up to 32) attributes of both the menu and title domains
VTS_PTT_SRPT	Part-of-Title search pointer table: for each title, the list of chapters, each as a (PGC number, program number) pair
VTS_PGCIT	The PGC information table for the title domain: every PGC in the title set
VTSM_PGCI_UT	Menu PGC information, organized by menu language
VTS_TMAPTI	Time map table: time-to-sector lookup used for time search
VTSM_C_ADT	Cell address table for the menu VOB
VTSM_VOBU_ADMAP	VOBU address map for the menu VOB
VTS_C_ADT	Cell address table for the title VOBs
VTS_VOBU_ADMAP	VOBU address map for the title VOBs

• C_ADT (Cell Address Table) lists each cell by VOB ID and cell ID with its start and end sector within the VOB set.
• VOBU_ADMAP is a flat list of the start sector of every VOBU in the VOB set, in order.
• VTS_TMAPTI contains one time map per PGC. A time map has entries at a fixed interval (1 to 255 seconds, set per map); each entry gives the sector of the VOBU nearest that time, so a player can seek by time without scanning.
• PGCI_UT tables (both VMGM_ and VTSM_) hold one language unit per menu language, identified by an ISO 639 two-letter code. Each language unit lists its menu PGCs with a menu type: title, root, subpicture, audio, angle, or chapter (PTT) menu.

Fixed field offsets

All multi-byte values in IFO files are big-endian. The management tables hold these fields at fixed byte offsets from the start of the IFO file.

File	Offset	Size	Field
VIDEO_TS.IFO	0x00	12	Identifier DVDVIDEO-VMG
VIDEO_TS.IFO	0x22	4	VMG category: byte 0x23 is the region mask (see Region codes)
VIDEO_TS.IFO	0x3E	2	Number of title sets
VIDEO_TS.IFO	0x84	4	Byte offset of the First Play PGC, from the start of the file (0 = none)
VIDEO_TS.IFO	0xC0	4	Sector of the menu VOB (VMGM_VOBS)
VIDEO_TS.IFO	0xC4	4	Sector of TT_SRPT
VIDEO_TS.IFO	0xD4	4	Sector of TXTDT_MG (0 = none)
VTS_nn_0.IFO	0x00	12	Identifier DVDVIDEO-VTS
VTS_nn_0.IFO	0xC0	4	Sector of the menu VOBs (VTSM_VOBS)
VTS_nn_0.IFO	0xC4	4	Sector of the title VOBs (VTSTT_VOBS)
VTS_nn_0.IFO	0xC8	4	Sector of VTS_PTT_SRPT
VTS_nn_0.IFO	0xCC	4	Sector of VTS_PGCIT
VTS_nn_0.IFO	0x200	2	Title-domain video attributes
VTS_nn_0.IFO	0x202	2	Number of audio streams (at most 8)
VTS_nn_0.IFO	0x204	8 each	Audio stream attributes
VTS_nn_0.IFO	0x254	2	Number of subpicture streams (at most 32)
VTS_nn_0.IFO	0x256	6 each	Subpicture stream attributes

Offset 0xC4 means different things in the two files: in VIDEO_TS.IFO it locates a table inside the same IFO (TT_SRPT), while in a VTS_nn_0.IFO it locates the title VOBs. Offset 0xC0 is the menu VOB in both. A title set’s menu VOB holds its own menu screens (for example a ratings notice), so the film does not start there.

Table sectors are counted from the start of the IFO file. The VTS title-VOB sector (0xC4) is also counted from the start of the IFO file, so the absolute disc sector of a VTS’s first title sector is the IFO file’s own first sector plus that value.

Video attributes (the first byte, at 0x200):

Bits	Field	Values
7–6	MPEG version
5–4	Video format	0 = NTSC, 1 = PAL; 2 and 3 are reserved
3–2	Display aspect ratio	0 = 4:3, 3 = 16:9; 1 and 2 are reserved
1–0	Permitted display modes

Audio attributes (8 bytes per stream):

Byte	Bits	Field	Values
0	7–5	Coding mode	0 = AC-3, 2 = MPEG-1 or MPEG-2 without extension stream, 3 = MPEG-2 with extension stream, 4 = LPCM, 6 = DTS
0	4	Multichannel extension present
0	3–2	Language type	0 = unspecified, 1 = language code in bytes 2–3
0	1–0	Application mode	0 = unspecified, 1 = karaoke, 2 = surround
1	5–4	Sample frequency	0 = 48 kHz, 1 = 96 kHz
1	2–0	Channel count minus one
2–3		Language code	Two lowercase ASCII letters (ISO 639-1); 00 00 = unspecified
4		Language code extension	Reserved
5		Code extension	See the table below

Subpicture attributes (6 bytes per stream):

Byte	Field	Values
0	Coding mode (bits 7–5), language type (bits 1–0)	Coding mode 0 = 2-bit run-length; language type 0 = unspecified, 1 = language code in bytes 2–3
2–3	Language code	Same form as the audio language code
4	Language code extension	Reserved
5	Code extension	See the table below

Code extension. Byte 5 of each audio attribute and byte 5 of each subpicture attribute states what kind of stream it is. Values not listed are unassigned.

Value	Audio stream	Subpicture stream
0	Not specified	Not specified
1	Normal	Normal
2	For the visually impaired	Large
3	Director’s comments	Children
4	Alternate director’s comments
5		Normal captions
6		Large captions
7		Children’s captions
9		Forced
13		Director’s comments
14		Large director’s comments
15		Director’s comments for children

The audio values are the values a player’s preferred-audio-extension register (SPRM 17) is compared against, and the subpicture values are those of the preferred-subpicture-extension register (SPRM 19). Several streams can carry the same language code and differ only in this byte, for example a normal track and a director’s-comments track in one language. A subpicture stream with code extension 9 holds forced subpictures (see Forced subpictures).

Language codes. The code is two lowercase ASCII letters. The language type bits of byte 0 say whether the field is meaningful: when the type is 0 the field is unspecified and can hold 00 00 or FF FF. The code is an ISO 639-1 two-letter code, so it needs mapping to a three-letter code for use where those are required. Spellings withdrawn from ISO 639-1 also occur: iw (Hebrew), in (Indonesian), ji (Yiddish), jw (Javanese) and mo (Moldavian).

What describes a stream. The IFO describes an audio stream by coding mode, channel count, sample rate, language and code extension, and a subpicture stream by language and code extension. The code extension is the field that marks commentary, caption, visually-impaired or forced streams; the IFO carries no title text for a stream. A stream’s physical ID comes from the PGC stream control, not from its position in the attribute list.

Title to PGC resolution

VTS_PTT_SRPT begins with a 2-byte count of titles at offset 0 and a 4-byte last-byte address at offset 4. From offset 8 there is one 4-byte offset per title, counted from the start of the table. Each offset locates that title’s list of 4-byte chapter entries, which runs to the next title’s offset (or to the last byte for the final title). The first two bytes of each chapter entry are the PGC number (1-based) of that chapter. The entries of one title may name different PGCs: a title can be stored as one PGC per chapter.

VTS_PGCIT begins with a 2-byte PGC count at offset 0. From offset 8 there is one 8-byte search entry per PGC, in PGC-number order; bytes 4–7 of each entry are the byte offset of that PGC, counted from the start of VTS_PGCIT.

A title is resolved by taking its VTS_TTN, looking up its first chapter entry in VTS_PTT_SRPT, and reading the PGC number from it.

Navigation model

Domains

Playback occurs in one of four domains, each with its own PGCs:

Domain	Purpose
First Play (FP)	A single PGC (FP_PGC, held in VMGI_MAT) that runs when the disc is loaded
Video Manager Menu (VMGM)	Disc-level menus, in VIDEO_TS.VOB
Video Title Set Menu (VTSM)	Per-title-set menus, in VTS_nn_0.VOB
Title (TT)	The program content, in VTS_nn_1..9.VOB

Titles, chapters, PGCs, programs and cells

• A title is the unit a user selects. Its structure is given in VTS_PTT_SRPT.
• A Part-of-Title (PTT) is a chapter: a (PGC, program) entry point within the title. A title can have more than 99 chapters; do not confuse the disc title limit with the PTT count. libdvdread checks for fewer than 1000 PTTs, and the on-disc count is a 16-bit field.
• A Program Chain (PGC) is the playback sequence. A PGC groups cells and is the object to which navigation commands, stream selections and the palette attach.
• A program is a run of consecutive cells within a PGC that marks an entry point. A PGC stores its program count in an 8-bit field, and a program map lists the first cell of each. The program count must not exceed the cell count.
• A cell is a contiguous run of VOBUs and the smallest independently addressable playback unit. A PGC has up to 255 cells. A cell is identified by its VOB ID (16 bits) and cell ID (8 bits).

A PGC contains:

Part	Contents
General information	Playback time, prohibited user operations, audio and subpicture stream control, next/previous/go-up PGC numbers, still time, and playback mode (sequential, random, shuffle)
Palette	16 colors in YCbCr, 4 bytes each
Subpicture control	Per-stream mapping of subpicture streams for each display mode (4:3, wide, letterbox, pan-scan)
Command table	Pre-commands, post-commands and cell commands
Program map	Entry cell of each program
Cell playback information table	One entry per cell
Cell position information table	VOB ID and cell ID of each cell

PGC fields sit at fixed byte offsets from the start of the PGC:

PGC offset	Size	Field
0x02	1	Number of programs
0x03	1	Number of cells
0x04	4	Playback time of the whole PGC (BCD time)
0x0C	8 × 2	Audio stream control, one 16-bit entry per logical audio stream
0x1C	32 × 4	Subpicture stream control, one 32-bit entry per logical subpicture stream
0xA4	16 × 4	Colour palette
0xE4	2	Offset of the command table, from the start of the PGC (0 = none)
0xE6	2	Offset of the program map, from the start of the PGC (0 = none)
0xE8	2	Offset of the cell playback information table, from the start of the PGC (0 = none)

For a sequential PGC, sum the cells on the selected playback path, taking one alternative from each angle block. Summing every angle cell overcounts the duration; commands, stills and non-sequential playback can also change the time experienced by a viewer.

BCD time

A playback time is 4 bytes: hours, minutes and seconds each as two BCD digits, then a fourth byte whose top two bits give the frame rate and whose low six bits are the frame count as BCD. Frame-rate bits 01 mean 25 frames per second and 11 mean 30000/1001 frames per second; 00 and 10 are not defined.

NTSC conversion needs an explicit convention. freemkv interprets this value as non-drop-frame timecode, not elapsed real time. Under that convention the seconds field advances every 30 frames at the NTSC rate, so conversion proceeds through a frame count: frames equal ((hours × 3600 + minutes × 60 + seconds) × 30 + frames) at the NTSC rate, or (… × 25 + frames) at the PAL rate, and real time is frames × 1001/30000 or frames / 25. This produces a duration 0.1 percent longer than treating the nominal frame count as 30 fps; it must not be applied indiscriminately to every DVD timestamp. A digit above 9 in a field is invalid.

NTSC timecode drift. Thirty frames of 1001/30000 s each last 1.001 s, so the timecode runs 0.1 percent behind real time: about 3.6 s per hour, growing with elapsed time (a chapter mark about 67 minutes in is roughly 4 s early when the fields are read as seconds). Under this interpretation no frame numbers are skipped to compensate. PAL has no such drift, because 25 frames last exactly 1 s. Worked examples at the NTSC rate:

Timecode	Frames	Real time
00:19:58:24	35 964	1 199.999 s (just under 20 minutes)
01:59:30:00	215 100	7 177.17 s (7170 s read as seconds)

This is freemkv’s conversion policy, not a settled statement of DVD conformance. libdvdnav’s dvdnav_convert_time uses literal hours/minutes/seconds and adds the frame component separately; it does not apply the 1.001 factor to the whole value. Check IFO-derived times against NAV presentation times and the elementary stream before applying a global NTSC correction. The examples above describe the frame-count interpretation used in freemkv’s IFO parser.

Damaged IFOs

A VTS_nn_0.BUP has the same layout and sector pointers as its VTS_nn_0.IFO, so when the IFO is damaged the BUP can be read in its place.

Cell playback information

The cell playback information table holds one 24-byte entry per cell, in playback order, at the PGC offset given by 0xE8:

Entry offset	Size	Field
+0	1	Category (bit fields below)
+1	1	Bit 7: playback mode (when set, the player enters still mode after each VOBU); bit 6: restricted
+2	1	Still time: 0 = none, 1–254 = seconds, 255 = infinite
+3	1	Cell command number
+4	4	Cell playback time (BCD time)
+8	4	Sector of the first VOBU
+20	4	Sector of the last VOBU’s last sector (the cell’s final sector)

The remaining bytes hold the end of the first ILVU (+12) and the start of the last VOBU (+16). A finite still therefore lasts at most 254 s, and a menu or still cell can hold one picture for that long, so a gap of many seconds between video timestamps in such a cell is content, not a clock fault. Sector values are counted from the start of the VTS title VOBs (VTSTT_VOBS); a cell spans its first sector through its last sector inclusive.

The category byte:

Bits	Field	Values
7–6	Block mode	0 = not in a block, 1 = first cell of the block, 2 = a cell inside the block, 3 = last cell of the block
5–4	Block type	0 = not in a block, 1 = angle block
3	Seamless playback	Seamless playback information is linked in the PCI; the cell can still carry the STC discontinuity flag, so seamless does not imply a continuous clock
2	Interleaved allocation	The cell’s sector range is shared with other cells’ interleaved units
1	STC discontinuity	The system clock restarts at the start of this cell
0	Seamless angle change

A cell position information table, with 4 bytes per cell, gives each cell’s VOB ID and cell ID.

Programs and chapters

The program map holds one byte per program, at the PGC offset given by 0xE6: the 1-based number of the first cell of that program. A chapter (PTT) points at a program.

Within one sequential PGC, the start time of a chapter is the sum of the playback times of the selected cells that come before the first cell of its program. The sum is taken in frames at the PGC’s frame rate and converted once, so that chapter marks land on frame boundaries; adding rounded seconds per cell drifts. The first chapter of that path starts at 0. A title spanning several PGCs also needs the preceding PGC paths and its navigation behavior; a PGC-local sum is not a title-wide time. A cell that is a non-first piece of an angle block (below) contributes no time, because only one angle of a block plays; an angle block counts once.

Chapter names. A chapter has a name only where the disc supplies one in TXTDT_MG. Discs may omit the text data entirely. A title’s chapter names are listed in TXTDT_MG in the order of the chapters as TT_SRPT counts them.

Angles and interleaving

A title can offer up to nine camera angles. The cells of an angle block are consecutive entries in the PGC’s cell table: the block’s first cell has block mode 1 and block type 1, the following cells of the block have block mode 2, and the final cell has block mode 3. Each of these cells is one angle’s version of the same scene. The first cell of the block is angle 1; the cells with block mode 2 and 3 are the other angles. Only one angle plays, so the other angles’ cells are not part of the playback timeline and their durations are not added to the time of the PGC.

To allow seamless switching, and seamless branching in general, the data of the cells involved is divided into Interleaved Units (ILVUs) that are interleaved on disc: one ILVU from angle 1, then one from angle 2, and so on, repeating. Cells with the interleaved allocation flag set therefore do not occupy their sector range alone: the range also holds other cells’ units (an alternate angle, or a second version of a branch).

Interleaved cells holding another program’s units. The other units need not be camera angles. A disc can store two language versions of the same programme in one VOB, sharing the picture of the scenes that are alike and interleaving units only where the versions differ (for example an English and a German cut of each episode). The cell of one version then spans sectors that also hold the other version’s units. Its first-to-last sector range is not what that cell plays: only the cell’s own units are, and playing every sector mixes the two versions and makes the timeline jump where they differ.

Walking interleaved units. In the DSI of a NAV pack (see NAV pack), two fields in the seamless playback information give, relative to the NAV pack’s own sector, the last sector of this interleaved unit and the first sector of the next interleaved unit of the same angle or scene. The unit therefore occupies the sectors from the NAV pack through the unit-end sector inclusive. The next unit begins at the NAV pack’s sector plus the next-unit offset. The chain ends when the next-unit offset is 0xFFFFFFFF (the end of interleaving); both fields are 0 for a non-interleaved unit, so a unit-end offset of 0 is not a valid unit. The chain belongs to an angle or scene within one VOB, not to a single cell: its units and next-unit pointers can run past the last sector of a cell, and a cell can begin or end in the middle of a unit. A unit can hold VOBUs of several consecutive cells of the same VOB. VTS_C_ADT lists an interleaved cell as one entry per interleaved unit, giving the cell’s sector pieces; a unit shared by two cells is listed under both.

Titles that share cells

A title is nothing more than a PGC’s list of cell sector ranges, resolved from TT_SRPT and VTS_PTT_SRPT. The tables do not give each title its own data: the cell tables of different titles, and of different PGCs, can name the same sector ranges, and no field marks a range as owned by one title. The disc stores each range once. The consequences:

• Play-all titles. A title can be the concatenation of other titles’ cells. A TV disc usually lists each episode as a title, plus one play-all title whose cell list contains every episode’s cell ranges, exactly, one after another. Its runtime is approximately the sum of the episodes’ runtimes, and its size is larger than any one episode. The episodes it holds start at different sectors. Because the play-all repeats the episodes’ sectors rather than carrying data of its own, adding the sizes of all titles counts the same sectors more than once.
• Shared opening and closing cells. Episodes can share a cell, for example an opening sequence or an end card; such a cell appears in every episode that uses it and appears once in the play-all. Sharing one cell does not make a title a play-all: a title is a play-all of another only when its cell list holds all of that title’s cell ranges. Two cuts that share most of their sectors but not all overlap partially, so neither contains the other.
• Parts that are not episodes. A short title inside a play-all, such as a logo or a recap, is contained by it without being an episode.
• The same episode twice. A disc can list one episode more than once, for example with a different audio track set. These titles begin at the same sector and may list identical cell ranges and the same duration. An episode that merely opens on the same intro clip as another has a different cell list and is different content.
• Decoy and duplicate titles. Some discs list many titles whose cell lists are identical to the feature’s; none is smaller than another, so none contains the others. A title with no cell ranges has no identity at all.

Registers

The navigation machine has two register banks, both 16 bits wide:

• 16 General Parameter Registers (GPRM 0–15) — scratch storage for disc authors. A GPRM can operate as a normal register or as a counter that counts elapsed time.
• 24 System Parameter Registers (SPRM 0–23) — player state. Selected entries:

SPRM	Meaning
0	Menu language
1	Audio stream number
2	Subpicture stream number and display flag
3	Angle number
4	Title number
5	Title number within the VTS
6	Current PGC number
7	Part-of-Title (chapter) number
8	Highlighted button
12	Parental management country code
13	Parental level
20	Player region code

Navigation commands

Navigation commands are 8 bytes each. They are stored in a PGC’s command table (pre-, post- and cell commands) and in the highlight button definitions of the NAV pack. The command set provides:

• Compare and branch — conditions on registers or immediates, with Goto and Break.
• Set — arithmetic and logic on GPRMs, and setting of system state such as audio stream, subpicture stream, angle, and parental level.
• Link — move within the current domain (to a PGC, program, cell, or the previous or next of these).
• Jump — leave the current domain to a title, a specific title in a VTS, a PGC, or a menu.
• Call — enter a menu from the title domain, with a resume point so that playback can return afterward.

Commands that combine a Set with a Link exist in a single 8-byte form.

Command tables

A PGC’s command table is located by the 16-bit offset at PGC 0xE4. Its first 16-bit field is the number of pre-commands; the commands themselves follow from table offset 8, 8 bytes each. The pre, post and cell command lists together hold at most 128 commands. The First Play PGC of VIDEO_TS.IFO is read the same way; its pre-commands may select a title directly with a JumpTT (commonly a logo or warning title rather than the feature) or jump to a menu.

Command encoding

The 8 bytes read as a big-endian value. Byte numbers below are counted from 0.

Byte 0 bits 7–5	Command family
0	Special: Goto, Break, SetTmpPML
1	Link (bit 4 = 0) or Jump/Call (bit 4 = 1)
2	SetSystem
3	SetGPRM
4–6	Compound forms that combine a Set with a Compare and a Link

Byte 1 bits 3–0 select the sub-command within a family. Byte 1 bits 6–4 hold an optional compare operator that guards the command; when the comparison is false the command has no effect and execution continues with the next line. Byte 1 bit 7 says whether the right-hand operand is an immediate.

Compare operator	Meaning
0	No comparison (always executes)
1	Bitwise AND is non-zero
2	Equal
3	Not equal
4	Greater than or equal
5	Greater than
6	Less than or equal
7	Less than

The compare operands sit in different bytes by family:

Family	Left register	Right operand
Special, Link	byte 3	immediate in bytes 4–5, or register in byte 5
Jump/Call, SetSystem	byte 6	register in byte 7
SetGPRM	byte 2	immediate in bytes 6–7, or register in byte 7

A register operand below 16 names a GPRM; a value of 0x80 or more names SPRM number (value minus 0x80).

Family	Sub-command (byte 1 bits 3–0)	Operands
Special	1 Goto	line number in byte 7 (1-based, within the same list)
Special	2 Break	ends the list
Special	3 SetTmpPML	sets the parental level in SPRM 13, then goes to the line in byte 7
Jump	1 Exit
Jump	2 JumpTT	VMG title number in byte 5 (low 7 bits)
Jump	3 JumpVTS_TT	title number within the current VTS in byte 5 (low 7 bits)
Jump	5 JumpVTS_PTT	title number in byte 5 (low 7 bits), chapter in bytes 2–3 (low 10 bits)
Jump	6 JumpSS	target in byte 5 bits 7–6: 0 First Play; 1 VMG menu (menu id in byte 5 low 4 bits); 2 VTS menu (VTS number in byte 4, title in byte 3, menu id in byte 5 low 4 bits); 3 a VMG menu PGC (PGC number in bytes 2–3, low 15 bits)
Jump	8 CallSS	target selector in byte 5 bits 7–6
Link	1 LinkSub	link code in byte 7 (low 5 bits); codes above 0x10 are undefined
Link	4 LinkPGCN	PGC number in bytes 6–7 (low 15 bits)
Link	5 LinkPTTN	chapter in bytes 6–7 (low 10 bits)
Link	6 LinkPGN	program number in byte 7 (low 7 bits)
Link	7 LinkCN	cell number in byte 7

A Link with sub-command 0 links nowhere. SetSystem and SetGPRM commands also carry a trailing link in byte 1 bits 3–0, using the same codes as the Link family.

SetGPRM. Byte 0 bit 4 says whether the source value is an immediate (bytes 4–5) or a register (byte 5); the destination GPRM is the low 4 bits of byte 3; byte 0 bits 3–0 give the operation:

Operation	Meaning
1	Move
2	Swap: exchange the destination with the register named by the low 4 bits of byte 5
3	Add
4	Subtract
5	Multiply
6	Divide
7	Modulo
8	Random
9	AND
10	OR
11	XOR

Reference players saturate addition and multiplication at 0xFFFF, clamp subtraction at 0, and return 0xFFFF for division or modulo by zero.

SetSystem. Byte 0 bits 3–0 give the operation. Operation 3 is SetGPRMMD: it stores a value (an immediate in bytes 2–3, or the register in byte 3, chosen by byte 0 bit 4) into the GPRM given by the low 4 bits of byte 5, and sets that register’s mode from byte 5 bit 7 (1 = counter mode, where the register counts elapsed time). The mode is applied even when the command’s compare is false. The other SetSystem operations write SPRMs.

Program stream

A VOB is an MPEG-2 Program Stream made of 2048-byte packs, one pack per sector. Each pack begins with a 14-byte pack header (start code 00 00 01 BA) carrying the System Clock Reference (SCR): a 33-bit base counting at 90 kHz plus a 9-bit extension at 27 MHz. The combined multiplex rate is limited to 10.08 Mbit/s, of which video may use at most 9.8 Mbit/s.

Video Object Units

A VOB is divided into VOBUs. A VOBU holds a whole number of video groups of pictures and nominally covers between 0.4 and 1.0 second of presentation time. It starts with a NAV pack, and its video begins with a sequence header and an I-picture, so a VOBU is an entry point for random access. A cell is a run of whole VOBUs.

NAV pack

The NAV pack is the first pack of every VOBU. It contains a pack header, a system header, and two packets on private_stream_2 (stream ID 0xBF). A sector is a NAV pack when it starts with the pack start code 00 00 01 BA, has the start code 00 00 01 BF at byte 0x400, and has sub-stream ID 0x01 at byte 0x406. The PCI packet comes first, in the space after the system header; the DSI packet starts at byte 0x400 of the pack and runs to the end of the sector. Each packet’s data begins with a one-byte sub-stream ID after its 6-byte PES header, so the DSI data starts at pack byte 0x407.

• PCI (Presentation Control Information), sub-stream ID 0x00:
  • PCI_GI — general information: the pack’s logical block number, a VOBU category field (which includes the Macrovision APS bits), user operation control, the VOBU start and end presentation times, and the elapsed time of the cell.
  • NSML_AGLI — angle information for non-seamless angle changes.
  • HLI — highlight information for menus: button groups, up to 36 buttons, the position, colour and contrast selection of each, and each button’s navigation command.
• DSI (Data Search Information), sub-stream ID 0x01:
  • DSI_GI — general information: the NAV pack’s SCR and logical block number, the end addresses of the VOBU and of its first, second and third reference pictures, and the VOB ID and cell ID.
  • SML_PBI — seamless playback information, including the ILVU addresses and sizes.
  • SML_AGLI — angle information for seamless angle changes, with a destination address for each of the nine angles.
  • VOBU_SRI — search information: relative addresses of VOBUs at forward and backward time offsets, for fast play.
  • SYNCI — synchronisation information tying audio and subpicture packets to the VOBU.

PCI_GI, counted from the first byte after the PCI sub-stream ID:

Offset	Size	Field
0	4	Logical block number of this NAV pack
4	2	VOBU category
6	2	Reserved
8	4	User operation control
12	4	VOBU start presentation time (90 kHz)
16	4	VOBU end presentation time (90 kHz)

DSI_GI, counted from the first byte after the DSI sub-stream ID (it is 32 bytes long):

Offset	Size	Field
0	4	SCR of this NAV pack
4	4	Logical block number of this NAV pack
8	4	End address of the VOBU
12	4	End address of the first reference picture
16	4	End address of the second reference picture
20	4	End address of the third reference picture
24	2	VOB ID
26	1	Reserved
27	1	Cell ID

SML_PBI follows DSI_GI directly, at DSI offset 32:

SML_PBI offset	Size	Field
0	2	Category flags
2	4	End of this interleaved unit, in sectors from this NAV pack
6	4	Start of the next interleaved unit, in sectors from this NAV pack; 0xFFFFFFFF means there is none (0 in a non-interleaved unit); 0x7FFFFFFF is the corresponding “none” value of the SML_AGLI angle entries

Which cell a VOBU belongs to. The VOB ID and cell ID in DSI_GI name the cell that owns the VOBU. The first NAV pack of a cell names that cell. Where the sector range of one cell also holds interleaved units of another program, a NAV pack that names a different pair opens a VOBU of another cell; within a unit shared by two cells of the same VOB, these IDs place the boundary.

Timestamps

Elementary-stream packets carry PTS (and, for video with reordered pictures, DTS) values on the 90 kHz clock. A PTS or DTS is a 5-byte field of 33 bits with a marker bit that must be set at the end of bytes 0, 2 and 4; a field with a cleared marker is malformed. The PES header carrying them has its PTS/DTS flags in the top two bits of its second flags byte: 10 = PTS only, 11 = PTS and DTS; the PTS follows the 3-byte fixed part of the PES header (flags, flags, header length), and the DTS follows the PTS.

Clock restarts. Each VOB, and each cell whose STC discontinuity flag is set, may restart the system clock, so PTS values are continuous only within a stretch of seamless playback. The PCI gives the presentation window of every VOBU: its start and end time. Within a continuous stretch each VOBU starts exactly where the previous VOBU ended. Where a VOBU’s start time does not follow the previous VOBU’s end time, the clock has restarted and the timestamps of everything from that VOBU onward are on a new base. A change of VOB can restart the clock, and the cell that begins it then has the STC discontinuity flag set. Example: one VOB’s clock ran from 0.1 s to 126.6 s and the next VOB restarted at 0.07 s.

Edge cases in timing

• Timestamps are therefore not monotonic across a title: playback timing across a VOB or cell join is defined by the PCI times, not by the raw PES timestamps. A restart shifts the timestamps of every track at once.
• Streams are multiplexed with different lead times, so at a join the audio and subpicture packets of the next segment can arrive before the first video picture of that segment. Such audio can already carry the new clock’s timestamps (for example a value near 0) while video of the previous segment is still running.
• A PTS or DTS is a 33-bit count of 90 kHz ticks and wraps after 2^33 ticks, about 26.5 hours. A drop of about 2^33 ticks followed by normal spacing is a wrap, not a clock restart.
• The SCR values of successive packs in a program stream are at most 0.7 s apart.
• The pack header’s program mux rate field is in units of 50 bytes per second; the DVD maximum of 10.08 Mbit/s is 25 200 units.
• A PES header carries a PTS only on a packet in which an access unit starts, and the PTS belongs to the first access unit that starts in that packet. A video picture that starts after a preceding picture’s tail takes that packet’s PTS if it is the first picture beginning there; a picture merely continuing from an earlier packet does not. Video PTS values are typically present once per group of pictures; pictures without one are timed from temporal_reference and the field durations of the pictures before them.

Elementary streams

Audio other than MPEG audio, and all subpictures, are carried on private_stream_1 (stream ID 0xBD); the first payload byte is the sub-stream ID.

Stream ID	Carries
0xE0	Video
0xC0–0xC7	MPEG-1 or MPEG-2 audio (up to 8 streams)
0xBD	Private stream 1: AC-3, DTS, LPCM audio and subpictures, selected by sub-stream ID
0xBF	Private stream 2: NAV pack PCI and DSI

Sub-stream ID on 0xBD	Carries
0x20–0x3F	Subpicture streams (32)
0x80–0x87	AC-3 audio (8)
0x88–0x8F	DTS audio (8)
0xA0–0xA7	LPCM audio (8)

Other packet types between payload packets are the system header (0xBB), the program stream map (0xBC) and padding (0xBE); padding carries no data. A conforming program-stream PES has a non-zero packet length. H.222.0 permits zero-length video PES in transport streams. A tolerant demuxer may recover such a malformed program-stream packet by scanning for the next pack, system header, program end or valid PES start code; that is recovery behavior, not DVD framing. A raw 00 00 01 also occurs inside video data and is insufficient to identify a packet boundary. The low 3 bits of byte 13 of the pack header give the number of stuffing bytes after it, which extend the header past 14 bytes.

Sub-stream headers. After the sub-stream ID byte:

Sub-stream IDs	Header after the sub-stream ID	Then
0x80–0x8F (AC-3, DTS)	3 bytes: number of frame headers (1 byte), first access unit pointer (2 bytes)	The elementary stream
0xA0–0xA7 (LPCM)	The same 3 bytes	A 3-byte LPCM audio header, then the samples
0x20–0x3F (subpicture)	None	The subpicture data

In an AC-3 or DTS packet the PTS belongs to the first access unit that starts in the packet; the pointer locates it. A packet can hold several complete frames and still carry only that one PTS, so the times of the later frames follow from the frame duration (a DTS core frame of 512 samples at 48 kHz lasts 10.667 ms). A frame can straddle two packets.

Video

Video is MPEG-2 Main Profile at Main Level or MPEG-1, on stream ID 0xE0. Only 4:3 and 16:9 display aspect ratios are allowed. The pixel grid is anamorphic at 720×480 or 720×576 either way; the display shape comes from the aspect ratio, not from the frame size.

System	Frame rate	MPEG-2 resolutions	MPEG-1 resolution
NTSC	29.97	720×480, 704×480, 352×480, 352×240	352×240
PAL	25	720×576, 704×576, 352×576, 352×288	352×288

• Film material. NTSC film material at 23.976 frames per second is coded as 29.97 frames per second with 3:2 pulldown signalled by flags in the MPEG-2 picture coding extension (repeat_first_field and top_field_first) rather than by repeating pictures in the stream. PAL film material is normally coded at 25 frames per second.
• Widescreen. 16:9 pictures are coded anamorphically in the same frame size. The VTS video attributes specify which display modes are permitted on a 4:3 display: letterbox, pan-scan, or both. Pan-scan uses horizontal offsets carried in the MPEG-2 sequence display and picture display extensions.
• Sequence header fields. Counted from the first byte of the sequence start code 00 00 01 B3: the horizontal size is 12 bits starting at byte 4, the vertical size is the following 12 bits (bytes 5–6), and byte 7 holds the aspect ratio code in its high nibble and the frame rate code in its low nibble. Aspect codes: 1 = square samples, 2 = 4:3, 3 = 16:9, 4 = 2.21:1; 0 is forbidden. Frame rate codes: 1 = 24000/1001, 2 = 24, 3 = 25, 4 = 30000/1001, 5 = 30, 6 = 50, 7 = 60000/1001, 8 = 60; 0 is forbidden. DVD-Video uses 1, 3 and 4.
• Picture flags. The picture coding extension is the extension start code 00 00 01 B5 whose first byte has the identifier nibble 1000. Counted from the start code, byte 6 holds picture_structure in its low 2 bits (11 = frame picture, 01 = top field, 10 = bottom field); byte 7 holds top_field_first in bit 7 and repeat_first_field in bit 1; byte 8 holds progressive_frame in bit 7. The sequence extension is the 00 00 01 B5 whose identifier nibble is 0001; progressive_sequence is bit 3 of the byte at offset 5 from its start code.
• Field count per picture. A field picture lasts one field period. A frame picture with repeat_first_field clear lasts two. With repeat_first_field set, a frame picture lasts three field periods when progressive_sequence is 0 and progressive_frame is 1 (the film case), and two when progressive_frame is 0; when progressive_sequence is 1 it lasts six (top_field_first set) or four (clear). A film-sourced NTSC stream therefore alternates two- and three-field pictures, and the start of each picture follows the sum of the field periods before it rather than a fixed 1/29.97 s grid.

Soft telecine, interlaced and mixed material

• 23.976 coded inside 29.97. A film title on an NTSC disc declares 29.97 frames per second in its sequence header and in the IFO, but its pictures are progressive frames coded at 24000/1001 per second; the pulldown is carried by repeat_first_field. The coded frame count is 80 percent of what the declared rate implies. A field lasts 1001/60000 s (16.68 ms), so a two-field picture lasts 33.37 ms and a three-field picture 50.05 ms; the 2:3 cycle of two pictures covers five fields (83.42 ms), an average of 41.71 ms per picture.
• Flags are per picture. progressive_frame, top_field_first and repeat_first_field are set in each picture’s coding extension, so one title can change character mid-stream: film sections (progressive frames, repeat_first_field set on alternate frames, 23.976) can be followed by video sections (interlaced frames, repeat_first_field clear, 29.97), and back. The picture duration then changes at the switch, and no single frame rate describes the title; one rate describes only the dominant material.
• progressive_sequence and progressive_frame. progressive_sequence is a property of the whole sequence and progressive_frame of one picture. A picture is progressive when either is 1. The two flags do not have to agree with the declared scan.
• Progressive coding under an interlaced declaration. The IFO video attributes and the sequence header describe 480-line or 576-line interlaced video whether or not the pictures are coded progressive. Film and animation discs commonly set progressive_frame on every picture while progressive_sequence stays 0, so the content is progressive on a disc that declares interlace.
• Leaders. A progressive leader (a logo or studio card) can open an interlaced feature, and an interlaced leader can open a progressive one, so the first picture does not represent the title.
• Field order. Interlaced material is top-field-first or bottom-field-first, and the order is carried per frame picture in top_field_first. A frame can instead be coded as two field pictures, each with its own picture header, whose parity is given by picture_structure (01 = top field, 10 = bottom field); one displayed frame is then two coded pictures.
• Closed captions. NTSC line-21 caption data may be carried in the video stream’s user data, with its presence flagged in the video attributes.
• Groups of pictures. temporal_reference (10 bits, display order within the group) restarts at 0 at every GOP header. The last bits of the GOP header (byte 7 counted from the start code 00 00 01 B8) are closed_gop (bit 6) and broken_link (bit 5). A GOP with closed_gop clear is open: its leading B-pictures were coded with a forward reference in the previous GOP, so a stream that begins at that GOP (a title start, or a join after a broken_link GOP) has leading B-pictures that cannot be decoded. The I-picture of an open GOP comes first in coding order but is displayed after those B-pictures, so the display start of the GOP lies before the I-picture’s own PTS.
• Aspect code in MPEG-1. In MPEG-1 video the aspect codes are pel aspect ratios, so code 3 is not 16:9.
• Colour. Standard-definition DVD video is BT.470 B/G (PAL) or SMPTE 170M (NTSC) unless a sequence display extension carries colour_description; its colour_primaries and matrix_coefficients values are 1 = BT.709, 5 = BT.470 B/G, 6 = SMPTE 170M. Video is limited range (luma 16–235). A 720×480 frame is not 3:2: with no square pixels, the display shape comes only from the aspect field.

Audio

Each title set and menu declares its audio streams in its management table: up to 8 audio streams in a title set, each with a coding mode, channel count, language code and extension, and a quantisation or sample-rate field.

Coding	Notes
AC-3 (Dolby Digital)	Up to 5.1 channels, 48 kHz, maximum 448 kbit/s
DTS	Up to 5.1 channels, 48 kHz, optional in players; commonly 754 or 1509 kbit/s
LPCM	48 or 96 kHz, 16, 20 or 24 bits, up to 8 channels, maximum 6.144 Mbit/s
MPEG-1 / MPEG-2 audio	Layer II; up to 8 streams on stream IDs 0xC0–0xC7

An audio attribute entry describes one logical stream. The audio stream control field of a PGC (16 bits per logical stream, at PGC 0x0C) says which physical stream that logical stream is in this PGC: bit 15 set means the stream is present; bits 10–8 are the physical stream number n (bits 14–11 are reserved). The physical stream’s ID is derived from the coding mode and n:

Coding	Stream carrying physical stream n
AC-3	private_stream_1 sub-stream 0x80 + n
DTS	private_stream_1 sub-stream 0x88 + n
LPCM	private_stream_1 sub-stream 0xA0 + n
MPEG audio	PES stream ID 0xC0 + n

The number n is the physical stream number, not a count within a codec: a DTS stream declared after an AC-3 stream uses its own physical number, not a number restarted at 0. A PGC can mark several logical streams with the same physical stream, and some PGCs mark none present. Coding mode 3 declares an additional extension bit stream that carries the multichannel part of an MPEG-2 audio stream beyond its MPEG-1-compatible base channels.

Edge cases in audio streams

• Physical order does not follow quality or declaration order. The i-th declared audio stream does not have to sit on the i-th physical stream. A disc can place a 2.0 downmix on sub-stream 0x80 and the 5.1 main mix on another AC-3 sub-stream, while the attribute entry declares 5.1 for the stream. The PGC audio stream control, not the sub-stream number, says which physical stream a logical stream plays. A DTS stream on physical number 1 is sub-stream 0x89, not 0x88.
• A programme can open as 2.0. A feature often opens with logos or warnings whose audio is a 2.0 AC-3 stream on 0x80, and the 5.1 main mix begins a fraction of a second later on the same sub-stream. The first frames of a sub-stream therefore do not show its channel count: the first AC-3 frames can carry the 2/0 channel mode (acmod 2) and later frames the 3/2 mode with LFE (acmod 7, lfeon set). The AC-3 channel count is acmod (channels 2, 1, 2, 3, 3, 4, 4, 5 for values 0 to 7) plus lfeon.

LPCM audio header. The three bytes that follow the sub-stream header of an LPCM packet:

Byte	Bits	Field
0	7	Emphasis flag
0	6	Mute flag
0	4–0	Audio frame number within its group of frames
1	7–6	Quantisation: 0 = 16 bit, 1 = 20 bit, 2 = 24 bit; 3 is reserved
1	5–4	Sample rate: 0 = 48 kHz, 1 = 96 kHz; 2 and 3 are not used on DVD
1	2–0	Channel count minus one
2	7–5	Dynamic range X
2	4–0	Dynamic range Y (linear gain 2^(4 − (X + Y/30)))

Samples are big-endian and interleaved by channel. 16-bit samples are stored as plain 16-bit words. For 20-bit and 24-bit audio, samples are stored in groups: a group of g samples (2 for mono, 4 for every other channel count) is g 16-bit words holding the most significant 16 bits of each sample, followed by the remaining low bits of the whole group: one byte per sample for 24-bit audio, and one nibble per sample for 20-bit audio (the first sample of a pair in the high nibble), so a 20-bit group has g / 2 extra bytes.

Subpictures

Subpictures carry subtitles, menu highlights and graphics. A subpicture unit holds run-length-encoded bitmaps of 2 bits per pixel, so each pixel selects one of four colours. The four colours are taken from the 16-entry YCbCr palette of the current PGC, and each of the four has its own 4-bit contrast (transparency) value. The unit also holds display control sequences that give the display area, the colour and contrast selection, the start and stop times, and the addresses of the top-field and bottom-field pixel data, so the bitmap is interlaced. Up to 32 subpicture streams can be declared, selected by sub-stream IDs 0x20–0x3F. A PGC maps each declared stream to a physical stream number separately for each display mode (4:3, wide, letterbox, pan-scan).

Subpicture unit. A unit begins with a 2-byte size giving the unit’s total length including those two bytes. A unit can span several PES packets of the same sub-stream: only the first carries a PTS, and the continuation packets carry none. A unit is therefore complete when the bytes gathered reach the declared size. The size is at most 65535 bytes.

Palette. The PGC colour table (16 entries of 4 bytes, from PGC 0xA4) stores each entry as padding, Y, Cr, Cb, in that byte order: Cr precedes Cb. The values are studio range (luma 16–235, chroma 16–240).

Subpicture stream control. Each logical subpicture stream has a 32-bit entry at PGC 0x1C: bit 31 set means the stream is present in this PGC; bits 28–24 are the sub-stream number used when the display is 4:3, and bits 20–16 the number used when the display is wide (16:9). The physical sub-stream ID is 0x20 plus that number. Anamorphic discs interleave the separate 4:3, wide, letterbox and pan-scan variants of a stream, so a logical stream’s sub-stream number is not simply its position. Two logical streams may name the same number. A stream whose present bit is clear is not presented by that PGC, but its packets can still be multiplexed in the PGC’s cells, for example in cells shared with the PGC of another language.

Menu buttons are drawn by overlaying a highlight subpicture on the menu’s video; the HLI in the NAV pack selects which colours and contrast apply to the buttons in their normal, selected and activated states.

Display control sequences

After the pixel data, bytes 2–3 of the unit give the offset of the first display control sequence (SP_DCSQ). Each sequence is:

Offset	Size	Field
0	2	Delay: time after the unit’s PTS at which the commands run
2	2	Offset of the next sequence; equal to the sequence’s own offset in the last one
4		Commands, ending with 0xFF

The delay counts the 90 kHz clock divided by 1024, so one tick is 1024/90000 s (about 11.38 ms) and 0x0100 is about 2.91 s. A subpicture’s display time is the delay of the sequence that holds its stop command, and the stop can sit in a later sequence than the start.

Code	Name	Length (bytes)	Meaning
0x00	FSTA_DSP	1	Forced start display
0x01	STA_DSP	1	Start display
0x02	STP_DSP	1	Stop display
0x03	SET_COLOR	3	Colour indices into the PGC palette: 2 data bytes, four 4-bit values
0x04	SET_CONTR	3	Contrast values: 2 data bytes, four 4-bit values
0x05	SET_DAREA	7	Display area: 6 data bytes, x and y start and end (12 bits each)
0x06	SET_DSPXA	5	Offsets of the top-field and bottom-field pixel data: two 16-bit values
0x07	CHG_COLCON	variable	Change colour and contrast in parts of the display area; a 16-bit length follows
0xFF	CMD_END	1	End of the command list of this sequence

Forced subpictures

FSTA_DSP (0x00) and STA_DSP (0x01) both start the display of the unit and take no operands. They differ in when the unit may be shown. A unit started with STA_DSP is shown only when the viewer has subpictures switched on (the display flag, bit 6 of SPRM 2, set) and has selected the stream carrying it. A unit started with FSTA_DSP is a forced unit: it is shown even when subtitles are switched off. The stream-number field of SPRM 2 takes the value 63 for forced display (62 means no stream).

Forced units carry text that must always be readable, such as the translation of a foreign-language passage or an on-screen sign. A subpicture stream made only of forced units is a forced-subtitle stream; its subpicture attribute can carry code extension 9 (see Code extension). A stream that holds both ordinary and forced units displays the ordinary ones only when subtitles are on. Menu subpictures also begin with FSTA_DSP, since menu buttons are shown whatever the viewer’s subtitle setting.

Stream limits

Item	Limit
Video Title Sets	99
Titles	99
Chapters (PTTs) per title	99
Programs per PGC	99
Cells per PGC	255
Angles	9
Audio streams per title set	8
Subpicture streams	32
Highlight buttons per menu	36
GPRM / SPRM	16 / 24
Title VOB files per VTS	9, each at most 1 GiB
Commands per PGC (pre, post and cell lists combined)	128
Multiplex rate	10.08 Mbit/s
Video bit rate	9.8 Mbit/s

Text data (TXTDT)

TXTDT_MG in VIDEO_TS.IFO can hold optional text: the disc name, title names, and chapter names, in one or more languages. It is entirely optional and many discs omit it. The structure has no official public specification; the layout below is the commonly documented one.

The 4-byte value at VIDEO_TS.IFO offset 0xD4 is the sector, counted from the start of the file, of the TXTDT_MG (0 = absent). All offsets below are from the start of the TXTDT_MG.

Offset	Size	Field
0x00	12	Identifier
0x0C	2	Reserved
0x0E	2	Number of language units
0x10	4	Offset of the last byte of the TXTDT_MG
0x14	8 each	Language unit pointers

Pointer offset	Size	Field
+0	2	Language code
+2	1	Reserved
+3	1	Character set
+4	4	Offset of the language unit

A language unit begins with 204 bytes of header: a 4-byte offset of the unit’s last byte, then up to 100 16-bit offsets, the first locating the disc-name entry and each following one the entry of the corresponding title in TT_SRPT order. At offset 204 of the unit is a 16-bit field holding twice the number of text entries, then 2 reserved bytes, then the entries from offset 208, 8 bytes each:

Entry offset	Size	Field
+0	1	Entry type
+6	2	Offset of the entry’s string, counted from offset 204 of the unit

A string ends at a tab (0x09) or a NUL byte.

Type	Meaning
0x01	Disc name
0x02	Title name
0x04	Chapter name

Other type values occur (for example 0x2E, an authoring-tool tag); these are private entries with no standard meaning.

Order and association. Entries are in disc order. A title entry (0x02) is followed by the chapter entries (0x04) of that title, one per chapter, until the next title entry. The first title entry corresponds to the first TT_SRPT entry, the second to the second, and so on. Each title’s chapter entries match the chapter count in its TT_SRPT entry.

Character set (byte 3 of the unit pointer): 0x01 is ISO 646 and 0x11 is ISO 8859-1; both are one byte per character.

Region coding and parental management

Region codes

The world is divided into eight regions, and a disc carries an 8-bit region mask in VMGI_MAT with one bit per region. The mask is the second byte of the 4-byte vmg_category field at 0x22, so it sits at byte 0x23 of VIDEO_TS.IFO. Bit n (bit 0 being the least significant) set means the disc is not playable in region n + 1, so the mask 0x00 marks a region-free disc. For example, 0xFD (all bits but bit 1 set) allows region 2 only, and 0x3F allows regions 7 and 8. The other bytes of vmg_category are not part of the region mask.

Region	Area
1	United States, Canada
2	Europe, Japan, Middle East, South Africa
3	South-East and East Asia
4	Australia, New Zealand, Latin America, Caribbean
5	Russia, Eastern Europe, India, Africa, North Korea, Mongolia
6	China
7	Reserved
8	Special international venues (aircraft, cruise ships)

Players hold their region in SPRM 20. Enforcement is the responsibility of the player or drive. The television system (NTSC at 525 lines and 60 fields, PAL at 625 lines and 50 fields) is a separate property, recorded in the video attributes.

Parental management

PTL_MAIT defines parental levels per country (ISO 3166 country code). Levels 1 through 8 are defined, where a higher level is more permissive. Each title’s TT_SRPT entry has a parental ID mask, and a title set may hold the same content as several alternate PGCs, each tagged with a parental level; the player selects the PGC that matches the level held in SPRM 13. This makes it possible for a single disc to present different cuts of the same title to different viewers.

Copy protection

Three protection mechanisms are associated with DVD media. They operate at different layers and are independent of one another.

CSS (Content Scramble System)

CSS protects pressed DVD-Video content. It is a 40-bit stream cipher. The elements are:

• Disc key. Stored in the lead-in of the disc, hidden from ordinary file reads, as a block that holds the disc key encrypted once under each of a set of player keys assigned to licensed manufacturers, plus a check value. A licensed player recovers the disc key using its own player key.
• Title keys. Each protected title set has its own 5-byte title key, stored in the sector headers of its VOB data and encrypted with the disc key.
• Sector scrambling. In each scrambled 2048-byte sector the first 128 bytes, containing the pack header and the start of the PES header, remain clear. The rest of the sector (bytes 0x80–0x7FF) is scrambled using a key stream derived from the title key. The flag that marks a sector as scrambled is the PES scrambling control field: bits 5–4 of the first PES header’s flags byte, non-zero when scrambled. In a pack with a 14-byte pack header and no stuffing, that byte is at sector offset 0x14; with n bytes of pack stuffing it is at 0x14 + n, and in an MPEG-1 system stream (12-byte pack header, marker bits 0010) those bytes are a packet length and a timestamp field, not a scrambling flag. NAV packs are not scrambled. IFO files, BUP files and filesystem structures are never scrambled: bytes that resemble the flag at offset 0x14 of such a sector are not scrambling flags.
• Edge cases.
  • Byte 0x14 of an IFO sector. The IFO files, BUP files and the UDF and ISO 9660 structures are never scrambled, but byte 0x14 of such a sector holds whatever the structure stores there, and bits 5–4 can be set. The second sector of a VIDEO_TS.IFO, which holds TT_SRPT, can begin 00 26 00 00 and hold 0x15 at offset 0x14: bits 5–4 read as 01, yet it is not a pack, and the flag means nothing there.
  • Clear sectors on a CSS disc. The scrambling flag is per sector, so scrambled and clear sectors can alternate. A disc can hold whole title sets, short stub titles or menu cells in the clear beside scrambled ones, and a title can open with a long run of clear sectors (a logo or rating card) before scrambled content begins. Such clear sectors can still have stray bits at 0x14 when the byte is read without checking for a pack.
  • Sector seed. The per-sector seed of the key stream is the 5 bytes at sector offsets 0x54–0x58, inside the clear first 128 bytes, combined with the title key.
• Authentication. When a drive and a host are separate devices (a PC), they perform a mutual challenge-response handshake across the drive interface before the drive will release the disc key and title keys. The handshake establishes a bus key, and the protected keys cross the interface encrypted under it. A drive that has not been authenticated refuses to read a scrambled sector: it returns CHECK CONDITION with sense key ILLEGAL REQUEST (5), ASC/ASCQ 6F/03 (“read of scrambled sector without authentication”), which distinguishes a scrambled sector from an unreadable one.

Region is enforced by the player or drive; the cipher itself does not encode a region.

CPRM (Content Protection for Recordable Media)

CPRM applies to recordable DVD media (such as DVD-RAM, DVD-R and DVD-RW), not to pressed DVD-Video discs. Each blank disc carries a unique media ID, and a Media Key Block (MKB) distributes keys to licensed devices in a way that allows revocation of compromised devices. A licensed device derives a media key from the MKB, combines it with the media ID, and uses the result to encrypt and decrypt content with the C2 cipher. The content is tied to the individual disc it was recorded on.

Macrovision analog protection (APS)

APS (Analog Protection System) is not encryption. It controls whether the player’s analog video output adds Macrovision’s copy-protection signal. The setting is carried as APS bits in the VOBU category field of the PCI and can vary from VOBU to VOBU. A related set of CGMS (Copy Generation Management System) bits in the sector’s copyright management data signals the copying permission of the content.

Glossary

Term	Meaning
VMG	Video Manager: the disc-level control structure and top menus
VTS	Video Title Set: a group of titles sharing attributes, with its menus
IFO	Information file holding the control tables
BUP	Backup copy of an IFO
VOB	Video Object: an MPEG-2 Program Stream file
VOBU	Video Object Unit: the NAV-pack-led unit of about 0.4 to 1.0 second
NAV pack	The first pack of each VOBU, carrying PCI and DSI
PCI / DSI	Presentation Control Information / Data Search Information
PGC	Program Chain: the playback sequence and its attached commands and palette
PTT	Part of Title: a chapter
Cell	The smallest addressable run of VOBUs in a PGC
ILVU	Interleaved Unit: the interleaving granule for angles and seamless branching
GPRM / SPRM	General / System Parameter Register
SCR	System Clock Reference in the pack header
PTS / DTS	Presentation / Decoding Time Stamp
HLI	Highlight Information: menu button definitions in the PCI
PTP / OTP	Parallel / Opposite Track Path on dual-layer discs
CSS	Content Scramble System
CPRM	Content Protection for Recordable Media
APS	Analog Protection System (Macrovision)
TT_SRPT	Title search pointer table: the disc’s title list
VTS_TTN	Title number within its title set
SPU	Subpicture unit: one subtitle or button bitmap with its display control sequence
TXTDT	Text data: optional disc, title and chapter names
STC	System Time Clock: the clock that PTS and DTS values refer to

References

Specifications define the formats; implementation links document concrete parser and recovery behavior. Research and community sources are identified separately. Observations from particular discs are not universal format guarantees.

Specifications

• DVD Forum, DVD Specifications for Read-Only Disc, Part 3: Video — licensed specification; the implementation references below are not substitutes for it
• ECMA-267: 120 mm DVD, Read-Only Disk — ecma-international.org
• ITU-T H.222.0 / ISO/IEC 13818-1, MPEG-2 Systems — program-stream, transport-stream and PES syntax
• ITU-T H.262 / ISO/IEC 13818-2, MPEG-2 Video
• ATSC A/52:2018, AC-3 and E-AC-3
• ECMA TR/112, Universal Disk Format — archived UDF revisions, including 1.02

Open-source implementations

Filesystem access and decryption

• libdvdcss, sector scrambling flag: css.c and libdvdcss.c

Navigation and metadata

• freemkv / libfreemkv — IFO, navigation and title parsing; implementation limits are identified in the text.
• libdvdread, IFO structures: ifo_types.h
• libdvdread, NAV pack structures: nav_types.h
• libdvdnav, command decoding: vmcmd.c and decoder.c
• libdvdnav, chapter and title times: searching.c

Elementary streams and codecs

• FFmpeg, DVD LPCM: pcm-dvd.c

Extraction and output

• freemkv — disc extraction application built on libfreemkv.
• FFmpeg — demuxing, decoding and remuxing.
• MKVToolNix — Matroska muxing and inspection.

Research and community references

• mpucoder’s DVD-Video pages: dvd.sourceforge.net/dvdinfo, notably IFO, VMG IFO, VTS IFO, PGC, PCI, DSI, VM commands, registers, subpictures, LPCM, MPEG streams and pack header