Cool external projects that use subtitles or do sorcery with a video stream
Note to GSoC applicants: Yes, you can use them. That's what open source is for. But if you decide to base on work on any of these: 1) Contact the original developer(s) and share your plan. They may be able to help you, but it's just a courtesy. 2) You proposal should consider that you are not starting from scratch. 3) Make sure you keep original credits intact, even in the cases where the license allows you to remove them. 4) Make sure you share your work with the original author.
Videodigest: Automatic Video Summaries
aeneas is a Python/C library and a set of tools to automagically synchronize audio and text (aka forced alignment).
lachesis automates the segmentation of a transcript into closed captions (CCs).
Pytube is a Python library (and command line tool) to download Youtube videos, including subtitles.