Merge remote-tracking branch 'cus/stable'

* cus/stable:
  ffmpeg: ensure that -fix_sub_duration doesnt create subtitles with zero duration
  ffmpeg: free empty subtitles as well in transcode_subtitles
  ffmpeg: do not pass possibly undefined subtitles to sub2video_update
Merged-by: Michael Niedermayer <michaelni@gmx.at>

ffmpeg.c

@@ -1807,25 +1807,32 @@ static int transcode_subtitles(InputStream *ist, AVPacket *pkt, int *got_output)
     }
 
     if (ist->fix_sub_duration) {
+        int end = 1;
         if (ist->prev_sub.got_output) {
-            int end = av_rescale(subtitle.pts - ist->prev_sub.subtitle.pts,
-                                 1000, AV_TIME_BASE);
+            end = av_rescale(subtitle.pts - ist->prev_sub.subtitle.pts,
+                             1000, AV_TIME_BASE);
             if (end < ist->prev_sub.subtitle.end_display_time) {
                 av_log(ist->st->codec, AV_LOG_DEBUG,
-                       "Subtitle duration reduced from %d to %d\n",
-                       ist->prev_sub.subtitle.end_display_time, end);
+                       "Subtitle duration reduced from %d to %d%s\n",
+                       ist->prev_sub.subtitle.end_display_time, end,
+                       end <= 0 ? ", dropping it" : "");
                 ist->prev_sub.subtitle.end_display_time = end;
             }
         }
         FFSWAP(int,        *got_output, ist->prev_sub.got_output);
         FFSWAP(int,        ret,         ist->prev_sub.ret);
         FFSWAP(AVSubtitle, subtitle,    ist->prev_sub.subtitle);
+        if (end <= 0)
+            goto out;
     }
 
+    if (!*got_output)
+        return ret;
+
     sub2video_update(ist, &subtitle);
 
-    if (!*got_output || !subtitle.num_rects)
-        return ret;
+    if (!subtitle.num_rects)
+        goto out;
 
     for (i = 0; i < nb_output_streams; i++) {
         OutputStream *ost = output_streams[i];
@@ -1836,6 +1843,7 @@ static int transcode_subtitles(InputStream *ist, AVPacket *pkt, int *got_output)
         do_subtitle_out(output_files[ost->file_index]->ctx, ost, ist, &subtitle);
     }
 
+out:
     avsubtitle_free(&subtitle);
     return ret;
 }