Replace Ctrl by Meta for volume shortcuts on MacOS

Ctrl+UP and Ctrl+DOWN are already used by the window manager on MacOS.

Use Cmd key instead (like on VLC).

README.md

@@ -134,8 +134,8 @@ scrcpy -f
  | click on `BACK`                        | `Ctrl`+`b` \| _Right-click²_  |
  | click on `APP_SWITCH`                  | `Ctrl`+`s`                    |
  | click on `MENU`                        | `Ctrl`+`m`                    |
- | click on `VOLUME_UP`                   | `Ctrl`+`↑` _(up)_             |
- | click on `VOLUME_DOWN`                 | `Ctrl`+`↓` _(down)_           |
+ | click on `VOLUME_UP`                   | `Ctrl`+`↑` _(up)_   (`Cmd`+`↑` on MacOS) |
+ | click on `VOLUME_DOWN`                 | `Ctrl`+`↓` _(down)_ (`Cmd`+`↓` on MacOS) |
  | click on `POWER`                       | `Ctrl`+`p`                    |
  | turn screen on                         | _Right-click²_                |
  | paste computer clipboard to device     | `Ctrl`+`v`                    |

app/src/input_manager.c

@@ -200,13 +200,21 @@ void input_manager_process_key(struct input_manager *input_manager,
                 }
                 return;
             case SDLK_DOWN:
+#ifdef __APPLE__
+                if (!ctrl && meta) {
+#else
                 if (ctrl && !meta) {
+#endif
                     // forward repeated events
                     action_volume_down(input_manager->controller, action);
                 }
                 return;
             case SDLK_UP:
+#ifdef __APPLE__
+                if (!ctrl && meta) {
+#else
                 if (ctrl && !meta) {
+#endif
                     // forward repeated events
                     action_volume_up(input_manager->controller, action);
                 }