The latest specification also includes HD bitmap support. (No fonts, no size, little to no color customizations).ĭVB Subtitling: This is a subtitle bitmap image that is compressed and sent as a DVB transport stream along with the DVB video and audio and decoded and displayed. This type of subtitles can’t be customized. What are the differences between DVB (FFMPEG’s dvb_sub) and DVB/Teletext (FFMPEG’s dvb_teletext) formats?ĭVB/Teletext: this is the standard for wrapping the good old EBU Teletext into a DVB signal. So, if you plan to include FFMPEG into your Closed-Captions workflow using the MPEG-TS container, please bear in mind that you won’t be able to transcode DVB/Teletext subtitles (e.g.: from “.srt” to DVB/Teletext), but you will be able to produce subtitles in the DVB (dvb_sub) format. In order to make FFMPEG able to decode DVB/Teletext stream data you will need to install the libzvbi library MPEG-TS it’s a standard format used in broadcast systems, such as DVB (Digital-Video-Broadcasting), ATSC (Advanced Television Systems Committee: an American set of standards for digital television transmission over terrestrial, cable and satellite networks) and IPTV (Internet Protocol Television).Īt the time of writing this article, FFMPEG (latest version 4.4) can handle (encode/decode/transcode) DVB/Subtitle format (dvb_sub), but can only decode (read or copy) DVB/Teletext Format (dvb_teletext) data streams. The “ MPEG-Transport-Stream“, (MPEG-TS, MTS) or simply transport stream (TS) is a standard digital container (which is a file format that allows multiple data streams to be embedded -or muxed- into a single file, usually along with metadata for identifying and further detailing those streams format) for transmission and storage of audio, video, and Program and System Information Protocol (PSIP) data.Īn MPEG-TS file containing 1 video stream, 2 audio streams and a subtitles (data) stream could be displayed by FFMPEG as follow: FFMPEG’s Output of an example MPEG-TS (.ts) file, with DVB/Teletext Subtitles In the broadcast world, the “Embed Captions” are often contained (muxed) into an MPEG-TS file (. “ Burned Subtitles” (or Open Captions): meaning that the subtitles are hardcoded (rendered) and always displayed in the video.įFMPEG can produce (encode/decode/transcode) both “Embed” and “Burned” captions, with some specific limitations for the DVB/Teletext format, as discussed later on this article.A “ Sidecar File“: a separate data file which contains the captions, in various subtitling formats.“ Embed Captions“: namely a stream of data (the captions), “injected” (or muxed) within the main video file.In the US and Canada, the standard for Closed-Captions is called “ CEA-708“, which is an evolution of the “ CEA-608” standard.The Teletext system was also used for a number of experimental systems, notably in the United States, but these were never as popular as their European counterparts and most closed by the early 1990s.In today’s digital world, “EBU Teletext” is now DVB/Teletext.More correct name is: “ CCIR Teletext System B“, while current standard name is “ Enhanced Teletext specification ETS 300 706“. EBU Teletext has long been the standard format for hard of hearing subtitling and multi-lingual subtitling in Europe, using the Teletext systems.BBC has provided the World’s first Teletext Service in 1974 ( Ceefax): RAI’s “Televideo” in Italy and other European Broadcasters followed, using Teletext also as a subtitles service.Closed Captions are intended for Viewers – watching television, or for Broadcasters – to increase reach, or meet regulatory requirements, or again for Service Providers – selling services for making TV accessible, distributing TV either traditionally or over the web and for Manufacturers – selling equipment in the broadcast chain and domestic environments.In the TV Broadcast world the term “ Closed Captions” is intended mainly for the hard of hearing audience (e.g.: subtitles that can be switched on and off and that are delivered as a separate asset from the main program).“ Subtitles” is a synonym for “Captions” in the US.Before getting started, here are some basic concepts for clarity purpose:
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