video: add VO framedropping mode

This mostly uses the same idea as with vo_vdpau.c, but much simplified.

On X11, it tries to get the display framerate with XF86VM, and limits
the frequency of new video frames against it. Note that this is an old
extension, and is confirmed not to work correctly with multi-monitor
setups. But we're using it because it was already around (it is also
used by vo_vdpau).

This attempts to predict the next vsync event by using the time of the
last frame and the display FPS. Even if that goes completely wrong,
the results are still relatively good.

On other systems, or if the X11 code doesn't return a display FPS, a
framerate of 1000 is assumed. This is infinite for all practical
purposes, and means that only frames which are definitely too late are
dropped. This probably has worse results, but is still useful.

"--framedrop=yes" is basically replaced with "--framedrop=decoder". The
old framedropping mode is kept around, and should perhaps be improved.
Dropping on the decoder level is still useful if decoding itself is too
slow.

4 files changed, 115 insertions, 17 deletions

diff --git a/video/out/vo.c b/video/out/vo.c
index e0c8d3ebed..72f98e8859 100644
--- a/video/out/vo.c
+++ b/video/out/vo.c
@@ -130,9 +130,16 @@ struct vo_internal {
 
     bool hasframe;
     bool request_redraw;
+    bool paused;
 
     int64_t flip_queue_offset; // queue flip events at most this much in advance
 
+    int64_t last_flip;
+    int64_t vsync_interval;
+    int64_t drop_count;
+    bool dropped_frame;             // the previous frame was dropped
+    struct mp_image *dropped_image; // used to possibly redraw the dropped frame
+
     int64_t wakeup_pts;             // time at which to pull frame from decoder
 
     bool rendering;                 // true if an image is being rendered
@@ -323,6 +330,11 @@ static void run_reconfig(void *p)
         vo->params = NULL;
     }
     forget_frames(vo); // implicitly synchronized
+
+    double display_fps = 1000.0; // assume infinite if unset
+    vo->driver->control(vo, VOCTRL_GET_DISPLAY_FPS, &display_fps);
+    vo->in->vsync_interval = 1e6 / display_fps;
+    MP_VERBOSE(vo, "Assuming %f FPS for framedrop.\n", display_fps);
 }
 
 int vo_reconfig(struct vo *vo, struct mp_image_params *params, int flags)
@@ -358,7 +370,9 @@ static void forget_frames(struct vo *vo)
 {
     struct vo_internal *in = vo->in;
     in->hasframe = false;
+    in->drop_count = 0;
     mp_image_unrefp(&in->frame_queued);
+    mp_image_unrefp(&in->dropped_image);
 }
 
 #ifndef __MINGW32__
@@ -496,6 +510,17 @@ void vo_wait_frame(struct vo *vo)
     pthread_mutex_unlock(&in->lock);
 }
 
+static int64_t prev_sync(struct vo *vo, int64_t ts)
+{
+    struct vo_internal *in = vo->in;
+
+    int64_t diff = (int64_t)(ts - in->last_flip);
+    int64_t offset = diff % MPMAX(in->vsync_interval, 1);
+    if (offset < 0)
+        offset += in->vsync_interval;
+    return ts - offset;
+}
+
 static bool render_frame(struct vo *vo)
 {
     struct vo_internal *in = vo->in;
@@ -510,33 +535,59 @@ static bool render_frame(struct vo *vo)
         return false;
     }
 
+    mp_image_unrefp(&in->dropped_image);
+
     in->rendering = true;
     in->frame_queued = NULL;
 
-    pthread_mutex_unlock(&in->lock);
+    // The next time a flip (probably) happens.
+    int64_t next_vsync = prev_sync(vo, mp_time_us()) + in->vsync_interval;
+    int64_t end_time = pts + duration;
+
+    in->dropped_frame = end_time < next_vsync;
+    in->dropped_frame &= !!(vo->global->opts->frame_dropping & 1);
+    in->dropped_frame &= !(vo->driver->caps & VO_CAP_FRAMEDROP) &&
+                         !vo->driver->untimed && !vo->driver->encode;
+    // Even if we're hopelessly behind, rather degrade to 10 FPS playback,
+    // instead of just freezing the display forever.
+    in->dropped_frame &= mp_time_us() - in->last_flip < 100 * 1000;
+
+    if (in->dropped_frame) {
+        in->drop_count += 1;
+        in->dropped_image = img;
+    } else {
+        pthread_mutex_unlock(&in->lock);
 
-    vo->driver->draw_image(vo, img);
+        vo->driver->draw_image(vo, img);
 
-    int64_t target = pts - in->flip_queue_offset;
-    while (1) {
-        int64_t now = mp_time_us();
-        if (target <= now)
-            break;
-        mp_sleep_us(target - now);
-    }
+        int64_t target = pts - in->flip_queue_offset;
+        while (1) {
+            int64_t now = mp_time_us();
+            if (target <= now)
+                break;
+            mp_sleep_us(target - now);
+        }
 
-    if (vo->driver->flip_page_timed)
-        vo->driver->flip_page_timed(vo, pts, duration);
-    else
-        vo->driver->flip_page(vo);
+        if (vo->driver->flip_page_timed)
+            vo->driver->flip_page_timed(vo, pts, duration);
+        else
+            vo->driver->flip_page(vo);
+
+        in->last_flip = mp_time_us();
+
+        MP_DBG(vo, "phase: %ld\n", (long)(in->last_flip % in->vsync_interval));
+
+        pthread_mutex_lock(&in->lock);
+    }
 
     vo->want_redraw = false;
 
-    pthread_mutex_lock(&in->lock);
     in->request_redraw = false;
     in->rendering = false;
+
     pthread_cond_signal(&in->wakeup); // for vo_wait_frame()
     mp_input_wakeup(vo->input_ctx);
+
     pthread_mutex_unlock(&in->lock);
 
     return true;
@@ -546,15 +597,28 @@ static void do_redraw(struct vo *vo)
 {
     struct vo_internal *in = vo->in;
 
+    vo->want_redraw = false;
+
     pthread_mutex_lock(&in->lock);
     in->request_redraw = false;
+    bool skip = !in->paused && in->dropped_frame;
+    struct mp_image *img = in->dropped_image;
+    if (!skip) {
+        in->dropped_image = NULL;
+        in->dropped_frame = false;
+    }
     pthread_mutex_unlock(&in->lock);
 
-    vo->want_redraw = false;
-
-    if (!vo->config_ok || vo->driver->control(vo, VOCTRL_REDRAW_FRAME, NULL) < 1)
+    if (!vo->config_ok || skip)
         return;
 
+    if (img) {
+        vo->driver->draw_image(vo, img);
+    } else {
+        if (vo->driver->control(vo, VOCTRL_REDRAW_FRAME, NULL) < 1)
+            return;
+    }
+
     if (vo->driver->flip_page_timed)
         vo->driver->flip_page_timed(vo, 0, -1);
     else
@@ -601,6 +665,27 @@ static void *vo_thread(void *ptr)
     return NULL;
 }
 
+void vo_set_paused(struct vo *vo, bool paused)
+{
+    struct vo_internal *in = vo->in;
+    pthread_mutex_lock(&in->lock);
+    if (in->paused != paused) {
+        in->paused = true;
+        if (in->paused && in->dropped_frame)
+            in->request_redraw = true;
+    }
+    pthread_mutex_unlock(&in->lock);
+    vo_control(vo, paused ? VOCTRL_PAUSE : VOCTRL_RESUME, NULL);
+}
+
+int64_t vo_get_drop_count(struct vo *vo)
+{
+    pthread_mutex_lock(&vo->in->lock);
+    int64_t r = vo->in->drop_count;
+    pthread_mutex_unlock(&vo->in->lock);
+    return r;
+}
+
 // Make the VO redraw the OSD at some point in the future.
 void vo_redraw(struct vo *vo)
 {
diff --git a/video/out/vo.h b/video/out/vo.h
index 0a8dca8c41..9077ab49b1 100644
--- a/video/out/vo.h
+++ b/video/out/vo.h
@@ -85,6 +85,7 @@ enum mp_voctrl {
     VOCTRL_SET_COMMAND_LINE,            // char**
 
     VOCTRL_GET_ICC_PROFILE_PATH,        // char**
+    VOCTRL_GET_DISPLAY_FPS,             // double*
 
     VOCTRL_GET_PREF_DEINT,              // int*
 };
@@ -134,6 +135,8 @@ struct voctrl_screenshot_args {
 
 // VO does handle mp_image_params.rotate in 90 degree steps
 #define VO_CAP_ROTATE90 1
+// VO does framedrop itself (vo_vdpau). Untimed/encoding VOs never drop.
+#define VO_CAP_FRAMEDROP 2
 
 struct vo;
 struct osd_state;
@@ -282,6 +285,8 @@ bool vo_has_frame(struct vo *vo);
 void vo_redraw(struct vo *vo);
 void vo_seek_reset(struct vo *vo);
 void vo_destroy(struct vo *vo);
+void vo_set_paused(struct vo *vo, bool paused);
+int64_t vo_get_drop_count(struct vo *vo);
 
 void vo_set_flip_queue_offset(struct vo *vo, int64_t us);
 void vo_wakeup(struct vo *vo);
diff --git a/video/out/vo_vdpau.c b/video/out/vo_vdpau.c
index 28f1a68c0c..e3498be1d1 100644
--- a/video/out/vo_vdpau.c
+++ b/video/out/vo_vdpau.c
@@ -1138,6 +1138,7 @@ static int control(struct vo *vo, uint32_t request, void *data)
 const struct vo_driver video_out_vdpau = {
     .description = "VDPAU with X11",
     .name = "vdpau",
+    .caps = VO_CAP_FRAMEDROP,
     .preinit = preinit,
     .query_format = query_format,
     .reconfig = reconfig,
diff --git a/video/out/x11_common.c b/video/out/x11_common.c
index 5c3c5aea0d..ef72fb4ca7 100644
--- a/video/out/x11_common.c
+++ b/video/out/x11_common.c
@@ -1492,6 +1492,13 @@ int vo_x11_control(struct vo *vo, int *events, int request, void *arg)
     case VOCTRL_UPDATE_WINDOW_TITLE:
         vo_x11_update_window_title(vo);
         return VO_TRUE;
+    case VOCTRL_GET_DISPLAY_FPS: {
+        double fps = vo_x11_vm_get_fps(vo);
+        if (fps <= 0)
+            break;
+        *(double *)arg = fps;
+        return VO_TRUE;
+    }
     }
     return VO_NOTIMPL;
 }