Code to download and convert Youtube XML annotations to ASS format
http://en.wikipedia.org/wiki/SubStation_Alpha#Advanced_SubStation_Alpha

Details about the ASS file format can be found at:
* http://www.matroska.org/technical/specs/subtitles/ssa.html
* http://moodub.free.fr/video/ass-specs.doc

This conversion script tries to maintain:

* Correct timing and text
* Font colour and background colour (can be improved)
* Positioning and width of subtitle text around the video

Positioning is hard to translated into ASS format because it uses Margins
instead of x/y and there's very little control over vertical spacing.

TODO:
* Support languages other than English
    * Done? Switched to Python3 and got this for free. Removed references to 'encode'
* Try to use ASS Picture Event lines to create transparent text boxes
* Use ffmpeg to mux the audio/video/subtitle streams into mkv
* What about automatic captions?
    * youtube-dl handles these now, so don't need to add this functionality
* Make a way to remove annotations like "Click Here", "Subscribe", etc.
* More that I'm forgetting.

Released under the CC-0 License

No code references were used while writing this parser, hence it's free of
derivative licensing problems.

Created for use by youtube-dl:
* ytdl-org/youtube-dl#90


$ ./youtube-ass.py -h
usage: youtube-ass.py [-h] [-c] [-d] (-a | -f FILENAME)

optional arguments:
  -h, --help            show this help message and exit
  -c, --youtube-dl-compatablity-mode
                        Use with youtube-dl --exec, strips the file extension
                        and replaces it with .annotations.xml, only functions
                        in single file mode
  -d, --delete-annotations
                        Delete annotations after processing them
  -a, --all             Process all *.annotations.xml files in the CWD
  -f FILENAME, --filename FILENAME
                        Single file name to process

to use with youtube-dl:
    Keep the annotation files
        youtube-dl --write-annotations --exec '/path/to/youtube-ass.py -c -f {}' [OPTIONS] URL [URL...]
    delete the annotation files when finished
        youtube-dl --write-annotations --exec '/path/to/youtube-ass.py -c -d -f {}' [OPTIONS] URL [URL...]