options: add --fit-border video option

Flag that is set by default. Reseting it will result in mpv trying to fit
client area with video instead of the whole window with border and
decorations on the screen.
Marked as (Windows only) for now until it's implemented on other platforms.

DOCS/man/options.rst

@@ -1805,6 +1805,12 @@ Window
     Play video with window border and decorations. Since this is on by
     default, use ``--no-border`` to disable the standard window decorations.
 
+``--fit-border``, ``--no-fit-border``
+    (Windows only) Fit the whole window with border and decorations on the
+    screen. Since this is on by default, use ``--no-fit-border`` to make mpv
+    try to only fit client area with video on the screen. This behavior only
+    applied to window/video with size exceeding size of the screen.
+
 ``--on-all-workspaces``
     (X11 only)
     Show the video window on all virtual desktops.

options/options.c

@@ -399,6 +399,7 @@ const m_option_t mp_opts[] = {
                ({"no", 0}, {"yes", 1}, {"immediate", 2})),
     OPT_FLAG("ontop", vo.ontop, M_OPT_FIXED),
     OPT_FLAG("border", vo.border, M_OPT_FIXED),
+    OPT_FLAG("fit-border", vo.fit_border, M_OPT_FIXED),
     OPT_FLAG("on-all-workspaces", vo.all_workspaces, M_OPT_FIXED),
 
     OPT_FLAG("window-dragging", allow_win_drag, CONF_GLOBAL),
@@ -708,6 +709,7 @@ const struct MPOpts mp_default_opts = {
         .keepaspect = 1,
         .keepaspect_window = 1,
         .border = 1,
+        .fit_border = 1,
         .WinID = -1,
         .window_scale = 1.0,
         .x11_bypass_compositor = 0,

options/options.h

@@ -12,6 +12,7 @@ typedef struct mp_vo_opts {
     int ontop;
     int fullscreen;
     int border;
+    int fit_border;
     int all_workspaces;
 
     int screen_id;