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, 4 insertions, 2 deletions

diff --git a/mpvcore/screenshot.c b/mpvcore/screenshot.c
index 161bfac1e5..181292474b 100644
--- a/mpvcore/screenshot.c
+++ b/mpvcore/screenshot.c
@@ -316,8 +316,10 @@ static struct mp_image *screenshot_get(struct MPContext *mpctx, int mode)
         struct voctrl_screenshot_args args =
                             { .full_window = (mode == MODE_FULL_WINDOW) };
 
-        struct vf_instance *vfilter = mpctx->sh_video->vfilter;
-        vfilter->control(vfilter, VFCTRL_SCREENSHOT, &args);
+        if (mpctx->sh_video && mpctx->sh_video->vfilter) {
+            struct vf_instance *vfilter = mpctx->sh_video->vfilter;
+            vfilter->control(vfilter, VFCTRL_SCREENSHOT, &args);
+        }
 
         if (!args.out_image)
             vo_control(mpctx->video_out, VOCTRL_SCREENSHOT, &args);