Timed text is the presentation of text media in synchrony with other media, such as audio and video.
Applications
Typical applications of timed text are the real-time
subtitles of foreign-language movies on the Web,
captioning for people lacking audio devices or having hearing impairments,
karaoke, scrolling news items or
teleprompter applications.
Timed text for MPEG-4 movies and cellphone media is specified in MPEG-4 Part 17 Timed Text, and its MIME type is specified by RFC 3839.
Markup language specifications
The W3C keeps two standards intended to regulate timed text on the
Internet: the Timed Text Markup Language (TTML)
[Glenn Adams (Ed.): Timed Text Markup Language (TTML) 1.0 - W3C Recommendation, 18 November 2010] and
WebVTT.
created additional metadata structures for use in TTML and developed a profile of TTML called
SMPTE-TT.
The
DECE incorporated the SMPTE Timed Text in their UltraViolet Common File Format specification.
Competing formats
Interoperability for timed text came up during the development of the SMIL 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.
Example
The following is an extract from the , in
SubRip format, for the 1916
Krazy Kat Bugolist film.
1
00:00:22,000 --> 00:00:27,000
I'll teach thee Bugology, Ignatzes
2
00:00:40,000 --> 00:00:43,000
Something tells me
3
00:00:58,000 --> 00:01:59,000
Look, Ignatz, a sleeping bee
The equivalent in W3C WebVTT is the following:
WEBVTT
00:22.000 --> 00:27.000
I'll teach thee Bugology, Ignatzes
00:40.000 --> 00:43.000
Something tells me
00:58.000 --> 01:59.000
Look, Ignatz, a sleeping bee
The equivalent in W3C TTML is the following:
I'll teach thee Bugology, Ignatzes
Look, Ignatz, a sleeping bee
See also
-
Text over IP
-
Subtitle (captioning)
External links
