player: can't render video properly with libmpv(0.38) on Linux (#825)

feeluown/player/mpvplayer.py

@@ -45,12 +45,12 @@ def __init__(self, _=None, audio_device=b'auto', winid=None,
  mpvkwargs['wid'] = winid
  self._version = _mpv_client_api_version()
 
- # old version libmpv can use opengl-cb
- if self._version < (1, 107):
-  mpvkwargs['vo'] = 'opengl-cb'
-  self.use_opengl_cb = True
- else:
-  self.use_opengl_cb = False
+ # From libmpv 0.38, libmpv is not the default vo.
+ # Note if vo is not set to libmpv, the video is rendered in mpv's
+ # native window instead of feeluown's mpvwidget (tested on KDE+wayland).
+ # On macOS, this option is optional. I believe the option is also required
+ # on Windows.
+ mpvkwargs['vo'] = 'libmpv'
 
  # set log_handler if you want to debug
  # mpvkwargs['log_handler'] = self.__log_handler