SBT

For each cinematic there is one SBT (SuBTitle) file found in Interface\Cinematics (locale-xxXX.MPQ). It contains localized subtitles for movies

Each entry is made of a timestamp and a text. The entries are divided by an empty line.

00:00:14:00 - 00:00:16:00
Mein Sohn,

00:00:02:06 - 00:00:11:01 (8 sec. 18 frames) 
Vier Jahre ist es nun her, dass sich die sterblichen Völker zusammenschlossen, um gemeinsam dem Ansturm der Brennenden Legion zu trotzen.

This shows that everything after the timestamp is ignored. (Which is proven by the source aswell.)

The timestamp is hr:min:sec:msec.