Ever more content is being delivered over IP connections and viewed on non-broadcast devices such as computers, tablets and mobiles. This brings a challenge to provide the same viewer experience as in a conventional broadcast situation.
Although most of these alternative devices can produce HD video and good quality audio to similar standards as a TV set, the same cannot be said of the subtitles.
In a conventional broadcast environment all video, audio and ancillary data services including subtitles or captions are delivered as part of a data stream using one of the major standards (DVB, ATSC or ISDB). The same systems are used for VOD and Catch-up TV where delivery is to an IP based Set Top Box and a conventional display device.
However in the new display devices the decoding and display is performed by a range of browsers or media players and there is far less standardisation.
For video and audio a wide range of codecs are available and can often be loaded or updated as required. For subtitles and captions there are a range of standards including SMIL, SRT, SAMI, TTML and DXFP but all of these are code based and the quality of implementation varies between media players and delivery formats, especially in a streaming, as opposed to file download, environment…….