Support I-frame playlists

The encoder supports I-frame playlists.3

An I-Frame only playlist is almost identical to a regular playlist. The only difference is that I-Frame playlists do not have an intrinsic duration. Instead, they 33represent an instant in time. In an I-frame only playlist with the EXT-X-I-FRAMES-ONLY tag, the EXTINF tag duration actually refers to the "span" of the I-frame.

This is the time between the presentation time of the I-frame in the media segment and the presentation time of the next I-frame in the playlist (or the end of the presentation if it is the last I-frame in the playlist).