core: add playback resume feature (manual/opt-in)

A "watch later" command is now mapped to Shift+Q. This quits the player
and stores the playback state in a config file in ~/.mpv/watch_later/.
When calling the player with the same file again, playback is resumed
at that time position.

It's also possible to make mpv save playback state always on quit with
the --save-position-on-quit option. Likewise, resuming can be disabled
with the --no-resume-playback option.

This also attempts to save some playback parameters, like fullscreen
state or track selection. This will unconditionally override config
settings and command line options (which is probably not what you would
expect, but in general nobody will really care about this). Some things
are not backed up, because that would cause various problems. Additional
subtitle files, video filters, etc. are not stored because that would be
too hard and fragile. Volume/mute state are not stored because it would
mess up if the system mixer is used, or if the system mixer was
readjusted in the meantime.

Basically, the tradeoff between perfect state restoration and
complexity/fragility makes it not worth to attempt to implement
it perfectly, even if the result is a little bit inconsistent.

1 files changed, 4 insertions, 0 deletions

diff --git a/DOCS/man/en/input.rst b/DOCS/man/en/input.rst
index 7938502573..6d1072353f 100644
--- a/DOCS/man/en/input.rst
+++ b/DOCS/man/en/input.rst
@@ -169,6 +169,10 @@ run "<command>"
 quit [<code>]
     Exit the player using the given exit code.
 
+quit_watch_later
+    Exit player, and store current playback position. Playing that file later
+    will seek to the previous position on start.
+
 sub_add "<file>"
     Load the given subtitle file. It's not selected as current subtitle after
     loading.