What is SRT?

The SubRip file format, as reported on the Matroska multimedia container format website, is "perhaps the most basic of all subtitle formats.” SubRip (SubRip Text) files are named with the extension .srt, and contain formatted lines of plain text in groups separated by a blank line. Subtitles are numbered sequentially, starting at 1. The timecode format used is: hours:minutes:seconds,milliseconds with time units fixed to two zero-padded digits and fractions fixed to three zero-padded digits (00:00:00,000). The fractional separator used is the comma, since the program was written in France. The subtitle separator, a blank line, is the double byte MS-DOSCR+LF pair, though the POSIX single byte linefeed is also well supported.

1. A numeric counter identifying each sequential subtitle

2. The time that the subtitle should appear on the screen, followed by --> and the time it should disappear

3. Subtitle text itself on one or more lines

4. A blank line containing no text, indicating the end of this subtitle

Compatibility:

The SubRip .srt file format is supported by most software video players listed in Comparison of video player software. For Windows software video players that do not support subtitle playback directly, the VSFilter DirectX filter displays SubRip and other subtitle formats. The SubRip format is supported directly by many subtitle creation/editing tools, and some hardware home media players. In August 2008, YouTube added subtitle support to its Flash video player under the "Closed Captioning" option - content producers can upload subtitles in SubRip format.

Related Software:

Macgo Mac Blu-ray Player: Display SRT format on your Mac.
Macgo Windows Blu-ray Player: Display SRT on Windows platforms.
Macgo Free Mac Media Player: Display SRT for Mac OS X.

Related Source:

How to add and set Subtitles to a Blu-ray movie?
How to sync audio, video, subtitle by Mac Blu-ray Player?

Further Reading:

.SRT SubRip file format specification - Derived from the SubRip source code in 2004.
SubRip (.SRT) subtitle features and support in players - comparison of .srt feature handling in a range of common players.