subler is a tool for manipulating
tx3g subtitles tracks for playback in iPod, Apple TV, iPhone and other QuickTime enabled devices. It can deal with video, audio, chapters, subtitles and closed captions tracks from
.mp4, as well as H.264, AAC, AC3 and other raw formats.
I’m using it to remux my old ripped DVDs from MKV into
.m4v with a great deal of success, and even fixing little niggles like offset audio in some old rips.
Since version 0.15, it can also convert
VOBSUB subtitles into 3GPP text subtitles by performing OCR via an embedded instance of Tesseract – it works fine for English subtitles, but seems somewhat off the mark for those with accented characters.