command: add vsync-ratio property

This is very "illustrative", unlike the video-speed-correction
property, and thus useful. It can also be used to observe scheduling
errors, which are not detected by the core. (These happen due to
rounding errors; possibly not evne our fault, but coming from
files with rounded timestamps and so on.)

2 files changed, 9 insertions, 0 deletions

diff --git a/DOCS/interface-changes.rst b/DOCS/interface-changes.rst
index b81312f8e9..dd42895203 100644
--- a/DOCS/interface-changes.rst
+++ b/DOCS/interface-changes.rst
@@ -19,6 +19,8 @@ Interface changes
 
 ::
 
+ --- mpv 0.14.0 ---
+    - add "vsync-ratio" property
  --- mpv 0.13.0 ---
     - remove VO opengl-cb frame queue suboptions (no replacement)
  --- mpv 0.12.0 ---
diff --git a/DOCS/man/input.rst b/DOCS/man/input.rst
index 50ac4dbfbf..0233dbf057 100644
--- a/DOCS/man/input.rst
+++ b/DOCS/man/input.rst
@@ -921,6 +921,13 @@ Property list
     (which can happen especially with bad source timestamps). For example,
     using the ``display-desync`` mode should never change this value from 0.
 
+``vsync-ratio``
+    For how many vsyncs a frame is displayed on average. This is available if
+    display-sync is active only. For 30 FPS video on a 60 Hz screen, this will
+    be 2. This is the moving average of what actually has been scheduled, so
+    24 FPS on 60 Hz will never remain exactly on 2.5, but jitter depending on
+    the last frame displayed.
+
 ``vo-delayed-frame-count``
     Estimated number of frames delayed due to external circumstances in
     display-sync mode. Note that in general, mpv has to guess that this is