MPEG-4 Part 17

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MPEG-4 is a suite of standards which has many "parts", where each part standardizes various entities related to multimedia, such as audio, video, and file formats. To know more about various parts and what they mean, please see the entry for MPEG-4.

MPEG-4 Part 17, or MPEG-4 Timed Text is the text based subtitle format for MPEG-4. It is also streamable, which was one of the main aspects when creating the format. It is mainly aimed for use in the .mp4 container, but can also be used in the .3gp container (as 3GPP Timed Text), which is technically almost identical with .mp4 but more used in cell phones. 3GPP Timed Text is exactly the same as MPEG-4 Timed Text when used in the .mp4 container. QuickTime Pro and MP4Box can create or produce these kind of subtitle streams out of various subtitle input formats. MP4Box uses the fourcc tx3g for MPEG-4 Timed Text because of its inherently higher compatibility. MPEG-4 Timed Text is heavily based on XML semantics.

The ISO document defining the Timed Text format is ISO 14496-17.