player: show subtitles on VO if --force-window is used

If a VO is created, but no video is playing (i.e. --force-window is
used), then until now no subtitles were shown. This is because VO
subtitle display normally depends on video frame timing. If there are no
video frames, there can be no subtitles.

Change this and add some code to handle this situation specifically. Set
a subtitle PTS manually and request VO redrawing manually, which gets
the subtitles rendered somehow.

This is kind of shaky. The subtitles are essentially sampled at
arbitrary times (such as when new audio data is decoded and pushed to
the AO, or on user interaction). To make a it slightly more consistent,
force a completely arbitrary minimum FPS of 10.

Other solutions (such as creating fake video) would be more intrusive or
would require VO-level API changes.

Fixes #3684.

3 files changed, 22 insertions, 0 deletions

diff --git a/sub/osd.c b/sub/osd.c
index dfe75b7698..bf6233a0b1 100644
--- a/sub/osd.c
+++ b/sub/osd.c
@@ -119,6 +119,7 @@ struct osd_state *osd_create(struct mpv_global *global)
         .opts = global->opts,
         .global = global,
         .log = mp_log_new(osd, global->log, "osd"),
+        .force_video_pts = MP_NOPTS_VALUE,
     };
     pthread_mutex_init(&osd->lock, NULL);
 
@@ -190,6 +191,21 @@ void osd_set_render_subs_in_filter(struct osd_state *osd, bool s)
     pthread_mutex_unlock(&osd->lock);
 }
 
+void osd_set_force_video_pts(struct osd_state *osd, double video_pts)
+{
+    pthread_mutex_lock(&osd->lock);
+    osd->force_video_pts = video_pts;
+    pthread_mutex_unlock(&osd->lock);
+}
+
+double osd_get_force_video_pts(struct osd_state *osd)
+{
+    pthread_mutex_lock(&osd->lock);
+    double pts = osd->force_video_pts;
+    pthread_mutex_unlock(&osd->lock);
+    return pts;
+}
+
 void osd_set_progbar(struct osd_state *osd, struct osd_progbar_state *s)
 {
     pthread_mutex_lock(&osd->lock);
@@ -288,6 +304,9 @@ void osd_draw(struct osd_state *osd, struct mp_osd_res res,
 {
     pthread_mutex_lock(&osd->lock);
 
+    if (osd->force_video_pts != MP_NOPTS_VALUE)
+        video_pts = osd->force_video_pts;
+
     if (draw_flags & OSD_DRAW_SUB_FILTER)
         draw_flags |= OSD_DRAW_SUB_ONLY;
 
diff --git a/sub/osd.h b/sub/osd.h
index cf66392904..755aca9969 100644
--- a/sub/osd.h
+++ b/sub/osd.h
@@ -155,6 +155,8 @@ void osd_set_sub(struct osd_state *osd, int index, struct dec_sub *dec_sub);
 
 bool osd_get_render_subs_in_filter(struct osd_state *osd);
 void osd_set_render_subs_in_filter(struct osd_state *osd, bool s);
+void osd_set_force_video_pts(struct osd_state *osd, double video_pts);
+double osd_get_force_video_pts(struct osd_state *osd);
 
 struct osd_progbar_state {
     int type;           // <0: disabled, 1-255: symbol, else: no symbol
diff --git a/sub/osd_state.h b/sub/osd_state.h
index fbccd85e70..cce415a1b9 100644
--- a/sub/osd_state.h
+++ b/sub/osd_state.h
@@ -67,6 +67,7 @@ struct osd_state {
     struct osd_object *objs[MAX_OSD_PARTS];
 
     bool render_subs_in_filter;
+    double force_video_pts;
 
     bool want_redraw;
     bool want_redraw_notification;