player: add --window-scale option

Requested. Works similar to the property with the same name.

DOCS/man/options.rst

@@ -1724,6 +1724,14 @@ Window
             (depending on the video aspect ratio, the width or height will be
             larger than 500 in order to keep the aspect ratio the same).
 
+``--window-scale=<factor>``
+    Resize the video window to a multiple (or fraction) of the video size. This
+    option is applied before ``--autofit`` and other options are applied (so
+    they override this option).
+
+    For example, ``--window-scale=0.5`` would show the window at half the
+    video size.
+
 ``--autosync=<factor>``
     Gradually adjusts the A/V sync based on audio delay measurements.
     Specifying ``--autosync=0``, the default, will cause frame timing to be

options/options.c

@@ -400,6 +400,7 @@ const m_option_t mp_opts[] = {
     OPT_SIZE_BOX("autofit", vo.autofit, 0),
     OPT_SIZE_BOX("autofit-larger", vo.autofit_larger, 0),
     OPT_SIZE_BOX("autofit-smaller", vo.autofit_smaller, 0),
+    OPT_FLOATRANGE("window-scale", vo.window_scale, 0, 0.001, 100),
     OPT_FLAG("force-window-position", vo.force_window_position, 0),
     // vo name (X classname) and window title strings
     OPT_STRING("x11-name", vo.winname, 0),
@@ -662,6 +663,7 @@ const struct MPOpts mp_default_opts = {
         .keepaspect_window = 1,
         .border = 1,
         .WinID = -1,
+        .window_scale = 1.0,
     },
     .allow_win_drag = 1,
     .wintitle = "mpv - ${?media-title:${media-title}}${!media-title:No file.}",

options/options.h

@@ -30,6 +30,7 @@ typedef struct mp_vo_opts {
     struct m_geometry autofit;
     struct m_geometry autofit_larger;
     struct m_geometry autofit_smaller;
+    float window_scale;
 
     int keepaspect;
     int keepaspect_window;

video/out/win_state.c

@@ -90,6 +90,8 @@ void vo_calc_window_geometry(struct vo *vo, const struct mp_rect *screen,
     int d_h = params.d_h;
     if ((vo->driver->caps & VO_CAP_ROTATE90) && params.rotate % 180 == 90)
         MPSWAP(int, d_w, d_h);
+    d_w = MPCLAMP(d_w * opts->window_scale, 1, 16000);
+    d_h = MPCLAMP(d_h * opts->window_scale, 1, 16000);
 
     int scr_w = screen->x1 - screen->x0;
     int scr_h = screen->y1 - screen->y0;