QuickTime 4 Reference

Time Stamps

When you export text and text descriptors from a text track, the text component also exports a time stamp for each sample. The time stamp indicates the starting and ending time of the sample, either relative to the start of the movie (kMovieExportAbsoluteTime ) or to the end of the previous sample (kMovieExportRelativeTime ). On import, the time stamps maintain the timing positions of the text samples relative to other media in the movie.

The format of a time stamp is



 
[HH:MM:SS.xxx]

where HH represents the number of hours, MM represents the number of minutes, SS represents the number of seconds, and xxx represents the mantissa (the fractional part of a second). The mantissa is expressed in the time scale of the text track. For example, if the time scale of the text track is 600, the time stamp [00:00:07.300] is interpreted as 7.5 seconds. If the time scale of the text track is 10, the time stamp [00:00:07.5] is also interpreted as 7.5 seconds. The maximum time scale for a text track is 10000.

When a text export component exports a text sample, it first exports the time stamp, followed by a return character. Then, it exports the sample's text and text descriptors. If a text sample does not contain any text, the text component exports the time stamp and return character, but no text.