Added AAC codec to mp4

[jeromegrosse]

Fix of the issue #344

[mbeacom]

@jeromegrosse Thanks for the PR.

AAC is an formatting/codec type for Audio (this extensions dict defines video codec types. Just looking for some clarification.
What issue does this resolve?

[ping]

I'm not the OP, but the problem is specified in #344
Without this PR, I cannot specify aac as the audio codec in write_videofile()

vidclip.write_videofile(output_file, codec='libx264', audio=True, audio_codec='aac')

[ghost]

@mbeacom, should we merge this pull request or should we look at adding an audio_codec to the dictionary?

[jeromegrosse]

@mbeacom
The extention_dict dictionnary is used by find_extention which is itself used by write_videofile when looking for the right codec to use for the audio file. This PR allows the possibility to use AAC and MP4.

The way I understood it, extention_dict is used to instinctively look up the audio and video codecs. Maybe it is semantically wrong though, and we should use two different dictionary, one for video codecs and one for audio codecs?

[mbeacom]

@jeromegrosse From the look of it, we should probably split up the dictionaries. This will require additional refactoring throughout the codebase to split up the dictionaries. @Earney Maybe we merge this and open a separate issue to track potentially splitting up the codec dictionaries?

[mbeacom]

Looks good until we can refactor the codec dictionary handling.

[ghost]

will do.