Automatically determine ffmpeg renditions to generate.

[monokal]

We currently have a list of dicts defining ffmpeg renditions to generate. This should be automatically populated based on the quality of the input video. E.g. Don't generate 4k HLS given a 720p input video.

self.renditions = [
            # {'name': '240p', 'resolution': '426x240', 'bitrate': '400k', 'audiorate': '64k'},
            # {'name': '360p', 'resolution': '640x360', 'bitrate': '700k', 'audiorate': '96k'},
            # {'name': '480p', 'resolution': '854x480', 'bitrate': '1250k', 'audiorate': '128k'},
            {'name': 'HD 720p', 'resolution': '1280x720', 'bitrate': '2500k', 'audiorate': '128k'},
            # {'name': 'HD 720p 60fps', 'resolution': '1280x720', 'bitrate': '3500k', 'audiorate': '128k'},
            {'name': 'Full HD 1080p', 'resolution': '1920x1080', 'bitrate': '4500k', 'audiorate': '192k'},
            # {'name': 'Full HD 1080p 60fps', 'resolution': '1920x1080', 'bitrate': '5800k', 'audiorate': '192k'},
            # {'name': '4k', 'resolution': '3840x2160', 'bitrate': '14000k', 'audiorate': '192k'},
            # {'name': '4k 60fps', 'resolution': '3840x2160', 'bitrate': '23000k', 'audiorate': '192k'}
        ]