manpage: add some minor documenation fixes

- replace the incorrect reference to --opengl-shader
- document a caveat when using --image-display-duration
- add some documentation on --vf=lavfi=

DOCS/man/mpv.rst

@@ -442,7 +442,7 @@ this is strongly discouraged and deprecated, except for ``-set``.
 
 Without suffix, the action taken is normally ``-set``.
 
-Some options (like ``--sub-file``, ``--audio-file``, ``--opengl-shader``) are
+Some options (like ``--sub-file``, ``--audio-file``, ``--glsl-shader``) are
 aliases for the proper option with ``-append`` action. For example,
 ``--sub-file`` is an alias for ``--sub-files-append``.
 

DOCS/man/options.rst

@@ -2250,6 +2250,13 @@ Window
     This option does not affect the framerate used for ``mf://`` or
     ``--merge-files``. For that, use ``--mf-fps`` instead.
 
+    Setting ``--image-display-duration`` hides the OSC and does not track
+    playback time on the command-line output, and also does not duplicate
+    the image frame when encoding. To force the player into "dumb mode"
+    and actually count out seconds, or to duplicate the image when
+    encoding, you need to use ``--demuxer=lavf --demuxer-lavf-o=loop=1``,
+    and use ``--length`` or ``--frames`` to stop after a particular time.
+
 ``--force-window=<yes|no|immediate>``
     Create a video output window even if there is no video. This can be useful
     when pretending that mpv is a GUI application. Currently, the window

DOCS/man/vf.rst

@@ -286,11 +286,14 @@ Available mpv-only filters are:
 
             If you want to use the full filter syntax with this option, you have
             to quote the filter graph in order to prevent mpv's syntax and the
-            filter graph syntax from clashing.
+            filter graph syntax from clashing. To prevent a quoting and escaping
+            mess, consider using ``--lavfi-complex`` if you know which video
+            track you want to use from the input file. (There is only one video
+            track for nearly all video files anyway.)
 
         .. admonition:: Examples
 
-            ``-vf lavfi=[gradfun=20:30,vflip]``
+            ``--vf=lavfi=[gradfun=20:30,vflip]``
                 ``gradfun`` filter with nonsense parameters, followed by a
                 ``vflip`` filter. (This demonstrates how libavfilter takes a
                 graph and not just a single filter.) The filter graph string is