From c61675320b6f04684677e7064b0d6e38f6b23547 Mon Sep 17 00:00:00 2001
From: wm4 <wm4@nowhere>
Date: Thu, 27 Aug 2015 23:45:02 +0200
Subject: sd_ass: assume negative durations are unknown durations, and handle
 them

The FFmpeg can officially not distinguish between unknown subtitle
durations, and subtitle durations being 0. (It documents the value 0
meaning unknown duration.)

In practice, at least the LRC demuxer signals unknown subtitle durations
with a negative value.

Assume negative durations mean unknown duration. Show subtitles with
unknown duration forever. Unless there's a subtitle event following it;
then reset the duration so that it ends on the new subtitle event.

Fixes #2244.
---
 sub/sd_ass.c | 32 +++++++++++++++++++++++++++-----
 1 file changed, 27 insertions(+), 5 deletions(-)

diff --git a/sub/sd_ass.c b/sub/sd_ass.c
index f8b1180560..baec35faa9 100644
--- a/sub/sd_ass.c
+++ b/sub/sd_ass.c
@@ -19,6 +19,7 @@
 #include <assert.h>
 #include <string.h>
 #include <math.h>
+#include <limits.h>
 
 #include <libavutil/common.h>
 #include <ass/ass.h>
@@ -39,6 +40,7 @@ struct sd_ass_priv {
     bool is_converted;
     struct sub_bitmap *parts;
     bool flush_on_seek;
+    int extend_event;
     char last_text[500];
     struct mp_image_params video_params;
     struct mp_image_params last_params;
@@ -65,6 +67,7 @@ static int init(struct sd *sd)
     struct sd_ass_priv *ctx = talloc_zero(NULL, struct sd_ass_priv);
     sd->priv = ctx;
 
+    ctx->extend_event = -1;
     ctx->is_converted = sd->converted_from != NULL;
 
     pthread_mutex_lock(sd->ass_lock);
@@ -100,16 +103,19 @@ static void decode(struct sd *sd, struct demux_packet *packet)
         ass_process_data(track, packet->buffer, packet->len);
         return;
     }
+
     // plaintext subs
     if (packet->pts == MP_NOPTS_VALUE) {
         MP_WARN(sd, "Subtitle without pts, ignored\n");
         return;
     }
-    if (packet->duration <= 0) {
-        MP_WARN(sd, "Subtitle without duration or "
-                "duration set to 0 at pts %f, ignored\n", packet->pts);
-        return;
+    if (ctx->extend_event >= 0 && ctx->extend_event < track->n_events) {
+        ASS_Event *event = &track->events[ctx->extend_event];
+        if (event->Start <= ipts)
+            event->Duration = ipts - event->Start;
+        ctx->extend_event = -1;
     }
+
     unsigned char *text = packet->buffer;
     if (!sd->no_remove_duplicates) {
         for (int i = 0; i < track->n_events; i++) {
@@ -121,6 +127,20 @@ static void decode(struct sd *sd, struct demux_packet *packet)
     }
     int eid = ass_alloc_event(track);
     ASS_Event *event = track->events + eid;
+
+    if (packet->duration == 0) {
+        MP_WARN(sd, "Subtitle without duration or "
+                "duration set to 0 at pts %f.\n", packet->pts);
+    }
+    if (packet->duration < 0) {
+        // Assume unknown duration. The FFmpeg API is very unclear about this.
+        MP_WARN(sd, "Assuming subtitle without duration at pts %f\n", packet->pts);
+        // _If_ there's a next subtitle, the duration will be adjusted again.
+        // If not, show it forever.
+        iduration = INT_MAX;
+        ctx->extend_event = eid;
+    }
+
     event->Start = ipts;
     event->Duration = iduration;
     event->Style = track->default_style;
@@ -349,8 +369,10 @@ static void fix_events(struct sd *sd)
 static void reset(struct sd *sd)
 {
     struct sd_ass_priv *ctx = sd->priv;
-    if (ctx->flush_on_seek || sd->opts->sub_clear_on_seek)
+    if (ctx->flush_on_seek || sd->opts->sub_clear_on_seek) {
         ass_flush_events(ctx->ass_track);
+        ctx->extend_event = -1;
+    }
     ctx->flush_on_seek = false;
 }
 
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