vo_opengl: fix interpolation with display-sync

At least I hope so.

Deriving the duration from the pts was not really correct. It doesn't
include speed adjustments, and becomes completely wrong of the user e.g.
changes the playback speed by a huge amount. Pass through the accurate
duration value by adding a new vo_frame field.

The value for vsync_offset was not correct either. We don't need the
error for the next frame, but the error for the current one. This wasn't
noticed because it makes no difference in symmetric cases, like 24 fps
on 60 Hz.

I'm still not entirely confident in the correctness of this, but it sure
is an improvement.

Also, remove the MP_STATS() calls - they're not really useful to debug
anything anymore.

1 files changed, 3 insertions, 0 deletions

diff --git a/video/out/vo.h b/video/out/vo.h
index 051638882b..87fd741c98 100644
--- a/video/out/vo.h
+++ b/video/out/vo.h
@@ -168,6 +168,9 @@ struct vo_frame {
     double vsync_interval;
     // "ideal" display time within the vsync
     double vsync_offset;
+    // "ideal" frame duration (can be different from num_vsyncs*vsync_interval
+    // up to a vsync) - valid for the entire frame, i.e. not changed for repeats
+    double ideal_frame_duration;
     // how often the frame will be repeated (does not include OSD redraws)
     int num_vsyncs;
     // Set if the current frame is repeated from the previous. It's guaranteed