core: add --force-window

This commit adds the --force-window option, which will cause mpv always
to create a window when started. This can be useful when pretending that
mpv is a GUI application (which it isn't, but users pretend anyway), and
playing audio files would run mpv in the background without giving a
window to control it.

This doesn't actually create the window immediately: it only does so
only after initializing playback and when it is clear that there won't
be any actual video. This could be a problem when starting slow or
completely stuck network streams (mpv would remain frozen in the
background), or if video initialization somehow is stuck forever in
an in-between state (like when the decoder doesn't output a video
frame, but doesn't return an error either). Well, we can pretend only
so much that mpv is a GUI application.

1 files changed, 14 insertions, 0 deletions

diff --git a/DOCS/man/en/options.rst b/DOCS/man/en/options.rst
index 9230529d54..cc0b7a4db2 100644
--- a/DOCS/man/en/options.rst
+++ b/DOCS/man/en/options.rst
@@ -804,6 +804,20 @@
     depending on GPU drivers and hardware. For other VOs, this just makes
     rendering slower.
 
+``--force-window``
+    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
+    always has the size 640x480, and is subject to ``--geometry``,
+    ``--autofit``, and similar options.
+
+    .. warning::
+
+        The window is created only after initialization (to make sure default
+        window placement still works if the video size is different from the
+        ``--force-window`` default window size). This can be a problem if
+        initialization doesn't work perfectly, such as when opening URLs with
+        bad network connection, or opening broken video files.
+
 ``--force-window-position``
     Forcefully move mpv's video output window to default location whenever
     there is a change in video parameters, video stream or file. This used to