vo_opengl: refactor smoothmotion -> interpolation

This replaces the old smoothmotion code by a more flexible tscale
option, which essentially allows any scaler to be used for interpolating
frames. (The actual "smoothmotion" scaler which behaves identical to the
old code does not currently exist, but it will be re-added in a later commit)

The only odd thing is that larger filters require a larger queue size
offset, which is currently set dynamically as it introduces some issues
when pausing or framestepping. Filters with a lower radius are not
affected as much, so this is identical to the old smoothmotion if the
smoothmotion interpolator is used.

1 files changed, 30 insertions, 42 deletions

diff --git a/DOCS/man/vo.rst b/DOCS/man/vo.rst
index a9a8e6db95..d76c95f987 100644
--- a/DOCS/man/vo.rst
+++ b/DOCS/man/vo.rst
@@ -426,11 +426,29 @@ Available video output drivers are:
         debug OpenGL context (which does nothing with current graphics drivers
         as of this writing).
 
+    ``interpolation``
+        Reduce stuttering caused by mismatches in the video fps and display
+        refresh rate (also known as judder).
+
+        This essentially attempts to interpolate the missing frames by
+        convoluting the video along the temporal axis. The filter used can be
+        controlled using the ``tscale`` setting.
+
+        Note that this relies on vsync to work, see ``swapinterval`` for more
+        information.
+
     ``swapinterval=<n>``
         Interval in displayed frames between two buffer swaps.
         1 is equivalent to enable VSYNC, 0 to disable VSYNC. Defaults to 1 if
         not specified.
 
+        Note that this depends on proper OpenGL vsync support. On some platforms
+        and drivers, this only works reliably when in fullscreen mode. It may
+        also require driver-specific hacks if using multiple monitors, to
+        ensure mpv syncs to the right one. Compositing window managers can
+        also lead to bad results, as can missing or incorrect display FPS
+        information (see ``--display-fps``).
+
     ``cscale=<filter>``
         As ``scale``, but for interpolating chroma information. If the image
         is not subsampled, this option is ignored entirely.
@@ -445,6 +463,18 @@ Available video output drivers are:
         See ``scale-param1``, ``scale-param2``, ``scale-radius`` and
         ``scale-antiring``.
 
+    ``tscale=<filter>``, ``tscale-param1``, ``tscale-param2``, ``tscale-antiring``
+        The filter used for interpolating the temporal axis (frames). This is
+        only used if ``interpolation`` is enabled. The only valid choices
+        for ``tscale`` are separable convolution filters (use ``tscale=help``
+        to get a list). The other options (``tscale-param1`` etc.) are
+        analogous to their ``scale`` counterparts. The default is ``mitchell``.
+
+        Note that the maximum supported filter radius is currently 3, and that
+        using filters with larger radius may introduce isues when pausing or
+        framestepping, proportional to the radius used. It is recommended to
+        stick to a radius of 1 or 2.
+
     ``linear-scaling``
         Scale in linear light. This is automatically enabled if
         ``target-prim``, ``target-trc``, ``icc-profile`` or
@@ -636,48 +666,6 @@ Available video output drivers are:
         Color used to draw parts of the mpv window not covered by video.
         See ``--osd-color`` option how colors are defined.
 
-    ``smoothmotion``
-        Reduce stuttering caused by mismatches in video fps and display
-        refresh rate (also known as judder).
-
-        Instead of drawing source frames for variable durations, smoothmotion
-        will blend frames that overlap the transition between two frames in
-        the source material.
-
-        For example, a 24 Hz clip played back on a 60 Hz display would normally
-        result in a pattern like this::
-
-            A A A B B C C C D D E E E F F
-
-        which has different lengths, alternating between 3 and 2. This
-        difference in frame duration is what causes judder.
-
-        With smoothmotion enabled, the pattern changes to::
-
-            A A A+B B B C C C+D D D E E E+F F F
-
-        where A+B is a blend of A and B. In this pattern, each frame gets a
-        (consistent) duration of roughly 2.5 - resulting in smooth motion.
-
-        GPU drivers or compositing window managers overriding vsync behavior
-        can lead to bad results. If the framerate is close to or over the
-        display refresh rate, results can be bad as well.
-
-        .. note:: On systems other than Linux or OS X, you currently must set
-                  the ``--display-fps`` option, or the results will be bad.
-
-    ``smoothmotion-threshold=<0.0-0.5>``
-        Mix threshold at which interpolation is skipped (default: 0.0 – never
-        skip).
-
-        For example, with a ``smoothmotion-threshold`` of 0.1, if the
-        smoothmotion algorithm would try to blend two frames by a ratio of
-        95% A + 5% B, it would simply display A instead. (Since the
-        distance, 0.05, is lower than the threshold)
-
-        Setting this to 0.5 would be similar to disabling smoothmotion
-        completely, since it would always just display the nearest frame.
-
 ``opengl-hq``
     Same as ``opengl``, but with default settings for high quality rendering.