Previously when using a libmpv instance to play multiple videos,
once --start was set there was no clear way to unset it. You could
use --start=0, but 0 does not always mean the beginning of the file
(especially when using --rebase-start-time=no). Looking up the start
timestamp and passing that in also does not always work, particularly
when the first timestamp is negative (since negative values to --start
have a special meaning).
This commit adds a new "none" value which maps to the internal
REL_TIME_NONE, matching the default value of the play_start option.
Aman Gupta
0c6a488ef9