Subpictures are graphic images that can be overlaid on top of the video and are used for subtitles and menus
Subpictures are graphics images which can be overlaid on top of video stills or sequences. They can be any height and width up to full screen (720 pixels by 480 or 576 lines) with 4 colors per pixel (2 bits) and are used for subtitles and menus.
Subpictures can be changed each frame, may fade in/out, wipe in or scroll up and down the screen.
Subtitles provide the display of text in any of up to 32 languages to complement the audio language channels. The text is stored on disc as graphics subpictures rather than closed caption encoded characters. This is a more flexible solution which accommodates any character set. The three colors available (plus transparent) can be used to soften/anti-alias the edge of the text characters and/or to make the text more readable against a varying background.
The three colors available can be preset and changed under program control by commands contained in program chains.
Subtitles must be synchronized with the video and audio track, particularly where the subtitles are used in addition to or in place of the audio to help the deaf or hard of hearing or to add another language where the audio for that language is not available.
Menus comprise MPEG stills or moving video with overlaid subpictures for highlighting menu buttons when selected or for providing additional text/graphics. When the user selects a menu button it must be highlighted to indicate which button is active and this can be done using subpictures and changing the color(s).
In the USA, DVD-Video discs can also provide Closed Captions (CC), which is a feature of a standard NTSC television signal for encoding text, like a simplified version of the teletext services used in Europe. A CC button on the player's remote control is used to display closed caption.