Subpictures

run-length compressed bitmaps that are overlayed ontop of the MPEG reconstructed video.

Applications include: Menus, sub-titles, karaoke, and simple animation.

Pixels are divided into four types: 1. background 2. Foregound 3. Empahsis-1 4. Emphasis-2

4 colors out of 16 color palette (4 colors are determined once per PGC).

4 out of 16 contrast values

up to a maximum of 32 sub-picture bitstreams. Each subpicture stream could, for example, could contain text from a particular language.

subpicture buffer size is restricted to 62 Kbytes. This means a maximum of 62 KB per GOP/cell. 32 Kbytes of this is control data.

Maximum number of bits per run-length coded line is 1440 bits.

Display area maximum: 720x480 (525/60) and 720x576 (625/50)

area, content, color, and contrast can be changed every video field

Sub-Picture Display Control Sequences (SP_DCSQ) control the presentation of Sub-pictures.

Presentation effects include: scroll up/down, fade in/out, etc.

  Structure of Sub-picture Decoding Unit (SPU):



    [ SPUH   ][        PXD        ][ DCSQT  ]



   SPUH:        Sub-picture Unit Header (size of SPU, start address of DCSQT)



   PXD:         Pixel Data (variable length run-length coded)



   DCSQT:       Display Control Sequence Table (one or more display control

                command sequences).

   



   DCSQT:   [DCSQ 0][DCSQ 1][DCSQ 2] ... [DCSQ n]



   DCSQ:  [Start time] [ Pointer to next DCSQ] [Command Sequence]



   Command Sequence:  [DCC 0][DCC 1]... [DCC m]

Display Control Commands (DCC):