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Timed text is the presentation of text media in synchrony with other media, such as audio and video.
Typical applications of timed text are the real-timesubtitling of foreign-language movies on theWeb,captioning for people lacking audio devices or havinghearing impairments,karaoke, scrolling news items orteleprompter applications.
Timed text forMPEG-4 movies and cellphone media is specified inMPEG-4 Part 17 Timed Text, and itsMIME type is specified by RFC 3839.
TheW3C keeps two standards intended to regulate timed text on theInternet: theTimed Text Markup Language (TTML)[1] andWebVTT.[2]SMPTE created additional metadata structures for use in TTML and developed a profile of TTML calledSMPTE-TT.[3] TheDECE incorporated the SMPTE Timed Text in theirUltraVioletCommon File Format specification.
Interoperability for timed text came up during the development of theSMIL 2.0 specification. Today, incompatible formats for captioning, subtitling and other forms of timed text are used on the Web. This means that when creating a SMIL presentation, the text portion often needs to be targeted to a particular playback environment. Moreover, the accessibility community relies heavily on captioning to make audiovisual content accessible. The lack of an interoperable format adds a significant additional cost to the costs of captioning Web content, which are already high.
The following is an extract from theEnglish closed captioning file, inSubRip format, for the 1916Krazy Kat Bugolist film.
100:00:22,000 --> 00:00:27,000I'll teach thee Bugology, Ignatzes2 00:00:40,000 --> 00:00:43,000 Something tells me3 00:00:58,000 --> 00:01:59,000 Look, Ignatz, a sleeping bee
The equivalent in W3CWebVTT is the following:
WEBVTT00:22.000 --> 00:27.000I'll teach thee Bugology, Ignatzes00:40.000 --> 00:43.000 Something tells me00:58.000 --> 01:59.000 Look, Ignatz, a sleeping bee
The equivalent in W3CTTML is the following:
<ttxmlns="http://www.w3.org/ns/ttml"><body><divbegin="22s"dur="5s"><p>I'llteachtheeBugology,Ignatzes</p></div><divbegin="40s"dur="3s"><p>Somethingtellsme</p></div><divbegin="58s"dur="61s"><p>Look,Ignatz,asleepingbee</p></div></body></tt>
