sub: implement "sub-seek 0"

For bitmap subs, implement it properly. For libass, you need newest git
master.

Fixes #2791.

2 files changed, 13 insertions, 6 deletions

diff --git a/player/command.c b/player/command.c
index 52718d60ae..c95e7d1315 100644
--- a/player/command.c
+++ b/player/command.c
@@ -4588,7 +4588,7 @@ int run_command(struct MPContext *mpctx, struct mp_cmd *cmd, struct mpv_node *re
                     // frame which actually shows the sub first (because video
                     // frame PTS and sub PTS rarely match exactly). Add some
                     // rounding for the mess of it.
-                    a[0] += 0.01 * (a[1] > 0 ? 1 : -1);
+                    a[0] += 0.01 * (a[1] >= 0 ? 1 : -1);
                     mark_seek(mpctx);
                     queue_seek(mpctx, MPSEEK_RELATIVE, a[0], MPSEEK_EXACT, false);
                     set_osd_function(mpctx, (a[0] > 0) ? OSD_FFW : OSD_REW);
diff --git a/sub/sd_lavc.c b/sub/sd_lavc.c
index 2da69e937e..4fbabaf864 100644
--- a/sub/sd_lavc.c
+++ b/sub/sd_lavc.c
@@ -398,15 +398,15 @@ static double step_sub(struct sd *sd, double now, int movement)
     struct sd_lavc_priv *priv = sd->priv;
     int best = -1;
     double target = now;
-    int direction = movement > 0 ? 1 : -1;
+    int direction = (movement > 0 ? 1 : -1) * !!movement;
 
-    if (movement == 0 || priv->num_seekpoints == 0)
+    if (priv->num_seekpoints == 0)
         return MP_NOPTS_VALUE;
 
     qsort(priv->seekpoints, priv->num_seekpoints, sizeof(priv->seekpoints[0]),
           compare_seekpoint);
 
-    while (movement) {
+    do {
         int closest = -1;
         double closest_time = 0;
         for (int i = 0; i < priv->num_seekpoints; i++) {
@@ -420,13 +420,20 @@ static double step_sub(struct sd *sd, double now, int movement)
                         closest_time = end;
                     }
                 }
-            } else {
+            } else if (direction > 0) {
                 if (start > target) {
                     if (closest < 0 || start < closest_time) {
                         closest = i;
                         closest_time = start;
                     }
                 }
+            } else {
+                if (start < target) {
+                    if (closest < 0 || start >= closest_time) {
+                        closest = i;
+                        closest_time = start;
+                    }
+                }
             }
         }
         if (closest < 0)
@@ -434,7 +441,7 @@ static double step_sub(struct sd *sd, double now, int movement)
         target = closest_time + direction;
         best = closest;
         movement -= direction;
-    }
+    } while (movement);
 
     return best < 0 ? 0 : priv->seekpoints[best].pts - now;
 }