video: add VO framedropping mode

This mostly uses the same idea as with vo_vdpau.c, but much simplified.

On X11, it tries to get the display framerate with XF86VM, and limits
the frequency of new video frames against it. Note that this is an old
extension, and is confirmed not to work correctly with multi-monitor
setups. But we're using it because it was already around (it is also
used by vo_vdpau).

This attempts to predict the next vsync event by using the time of the
last frame and the display FPS. Even if that goes completely wrong,
the results are still relatively good.

On other systems, or if the X11 code doesn't return a display FPS, a
framerate of 1000 is assumed. This is infinite for all practical
purposes, and means that only frames which are definitely too late are
dropped. This probably has worse results, but is still useful.

"--framedrop=yes" is basically replaced with "--framedrop=decoder". The
old framedropping mode is kept around, and should perhaps be improved.
Dropping on the decoder level is still useful if decoding itself is too
slow.

1 files changed, 7 insertions, 0 deletions

diff --git a/video/out/x11_common.c b/video/out/x11_common.c
index 5c3c5aea0d..ef72fb4ca7 100644
--- a/video/out/x11_common.c
+++ b/video/out/x11_common.c
@@ -1492,6 +1492,13 @@ int vo_x11_control(struct vo *vo, int *events, int request, void *arg)
     case VOCTRL_UPDATE_WINDOW_TITLE:
         vo_x11_update_window_title(vo);
         return VO_TRUE;
+    case VOCTRL_GET_DISPLAY_FPS: {
+        double fps = vo_x11_vm_get_fps(vo);
+        if (fps <= 0)
+            break;
+        *(double *)arg = fps;
+        return VO_TRUE;
+    }
     }
     return VO_NOTIMPL;
 }