manpage: document exit codes

DOCS/man/en/mpv.rst

@@ -588,6 +588,24 @@ libavformat:
     ``no_proxy``
         FIXME: Document this.
 
+EXIT CODES
+==========
+
+Normally **mpv** returns 0 as exit code after finishing playback successfully.
+If errors happen, the following exit codes can be returned:
+
+    :1: Error initializing mpv. This is also returned if unknown options are
+        passed to mpv.
+    :2: The file passed to mpv couldn't be played. This is somewhat fuzzy:
+        currently, playback of a file is considered to be successful if
+        initialization was mostly successful, even if playback fails
+        immediately after initialization.
+    :3: There were some files that could be played, and some files which
+        couldn't (using the definition of success from above).
+
+Note that quitting the player manually will always lead to exit code 0,
+overriding the exit code that would be returned normally. Also, the ``quit``
+input command can take an exit code: in this case, that exit code is returned.
 
 FILES
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