DVBsub

DVBSUB, short for DVB Subtitles, is a subtitle format used in Digital Video Broadcasting systems. It is defined by the DVB Project as part of the DVB subtitle specifications. DVBSUB subtitles are carried in a separate subpicture stream within an MPEG-2 or DVB transport stream and are rendered by the video decoder as an overlay on top of the video.

DVBSUB uses bitmap-based subtitles rather than encoded text. Subtitles are composed as a set of elements: pages, regions, objects, and color palettes (CLUTs). An object carries a bitmap image for a subtitle; a region defines where that image appears on the screen; one or more pages are formed from objects and regions to produce the final image. CLUTs define the color palette, and the stream includes timing data to synchronize appearance and disappearance with the video. The format supports layering and transparency to integrate the subtitle graphics with the video image.

Implementation and usage: DVBSUB is widely deployed in DVB broadcasting, including DVB-T, DVB-C, and DVB-S services. It is supported by most DVB receivers and by software players such as VLC and FFmpeg-based tools; decoding involves interpreting the page/region/object structure and rendering the bitmap overlay according to the palette and timing information. Some services also provide alternative subtitle methods, such as Teletext, depending on regional broadcast practices.

Standards and context: The DVB Subtitles specification is published by ETSI and forms part of the DVB suite, designed to work with broadcast streaming workflows and to support multiple languages and complex typography through image-based rendering. DVBSUB remains common in legacy and some current DVB broadcasts, particularly where precise graphical rendering is required.