1 files changed, 69 insertions, 2 deletions

diff --git a/sub/sd_ass.c b/sub/sd_ass.c
index 55c8d760e8..11943613f9 100644
--- a/sub/sd_ass.c
+++ b/sub/sd_ass.c
@@ -243,6 +243,72 @@ static void configure_ass(struct sd *sd, struct mp_osd_res *dim,
     ass_set_line_spacing(priv, set_line_spacing);
 }
 
+#define END(ev) ((ev)->Start + (ev)->Duration)
+
+static long long find_timestamp(struct sd *sd, double pts)
+{
+    struct sd_ass_priv *priv = sd->priv;
+    if (pts == MP_NOPTS_VALUE)
+        return 0;
+
+    long long ts = llrint(pts * 1000);
+
+    if (!sd->opts->sub_fix_timing)
+        return ts;
+
+    // Try to fix small gaps and overlaps.
+    ASS_Track *track = priv->ass_track;
+    int threshold = SUB_GAP_THRESHOLD * 1000;
+    int keep = SUB_GAP_KEEP * 1000;
+
+    // Find the "current" event.
+    ASS_Event *ev[2] = {0};
+    int n_ev = 0;
+    for (int n = 0; n < track->n_events; n++) {
+        ASS_Event *event = &track->events[n];
+        if (ts >= event->Start - threshold && ts <= END(event) + threshold) {
+            if (n_ev >= MP_ARRAY_SIZE(ev))
+                return ts; // multiple overlaps - give up (probably complex subs)
+            ev[n_ev++] = event;
+        }
+    }
+
+    if (n_ev != 2)
+        return ts;
+
+    // Simple/minor heuristic against destroying typesetting.
+    if (ev[0]->Style != ev[1]->Style)
+        return ts;
+
+    // Sort by start timestamps.
+    if (ev[0]->Start > ev[1]->Start)
+        MPSWAP(ASS_Event*, ev[0], ev[1]);
+
+    // We want to fix partial overlaps only.
+    if (END(ev[0]) >= END(ev[1]))
+        return ts;
+
+    if (ev[0]->Duration < keep || ev[1]->Duration < keep)
+        return ts;
+
+    // Gap between the events -> move ts to show the end of the first event.
+    if (ts >= END(ev[0]) && ts < ev[1]->Start && END(ev[0]) < ev[1]->Start &&
+        END(ev[0]) + threshold >= ev[1]->Start)
+        return END(ev[0]) - 1;
+
+    // Overlap -> move ts to the (exclusive) end of the first event.
+    // Relies on the fact that the ASS_Renderer has no overlap registered, even
+    // if there is one. This happens to work because we never render the
+    // overlapped state, and libass never resolves a collision.
+    if (ts >= ev[1]->Start && ts <= END(ev[0]) && END(ev[0]) > ev[1]->Start &&
+        END(ev[0]) <= ev[1]->Start + threshold)
+        return END(ev[0]);
+
+    return ts;
+}
+
+#undef END
+
 static void get_bitmaps(struct sd *sd, struct mp_osd_res dim, double pts,
                         struct sub_bitmaps *res)
 {
@@ -280,7 +346,8 @@ static void get_bitmaps(struct sd *sd, struct mp_osd_res dim, double pts,
     }
     if (no_ass)
         fill_plaintext(sd, pts);
-    mp_ass_render_frame(renderer, track, pts * 1000 + .5, &ctx->parts, res);
+    long long ts = find_timestamp(sd, pts);
+    mp_ass_render_frame(renderer, track, ts, &ctx->parts, res);
     talloc_steal(ctx, ctx->parts);
 
     if (!converted)
@@ -368,7 +435,7 @@ static char *get_text(struct sd *sd, double pts)
 
     if (pts == MP_NOPTS_VALUE)
         return NULL;
-    long long ipts = pts * 1000 + 0.5;
+    long long ipts = find_timestamp(sd, pts);
 
     struct buf b = {ctx->last_text, sizeof(ctx->last_text) - 1};