Subler is an Mac OS X app created to mux and tag mp4 files. The main features includes:

• Creation of tx3g subtitles tracks, compatible with all Apple's devices (iPod, AppleTV, iPhone, QuickTime?).
• Mux video, audio, chapters, subtitles and closed captions tracks from mov, mp4 and mkv.
• Raw formats: H.264 Elementary streams (.h264, .264), AAC (.aac), AC3 (.ac3), Scenarist (.scc), VobSub? (.idx).
• metadata editing and TMDb, TVDB and iTunes Store support.