lavc/ass: honor Default style.

The "Default" style written in the header is ignored unless you explicit
it in the Dialogue events (it was valid, just ignored). This requires an
update of the SubRip test since the ASS output obviously changes.

libavcodec/ass.c

@@ -38,7 +38,7 @@ int ff_ass_subtitle_header(AVCodecContext *avctx,
              "Style: Default,%s,%d,&H%x,&H%x,&H%x,&H%x,%d,%d,%d,1,1,0,%d,10,10,10,0,0\r\n"
              "\r\n"
              "[Events]\r\n"
-             "Format: Layer, Start, End, Text\r\n",
+             "Format: Layer, Start, End, Style, Text\r\n",
              font, font_size, color, color, back_color, back_color,
              -bold, -italic, -underline, alignment);
 
@@ -82,7 +82,7 @@ int ff_ass_add_rect(AVSubtitle *sub, const char *dialog,
             snprintf(s_end, sizeof(s_end), "9:59:59.99");
         else
             ts_to_string(s_end, sizeof(s_end), ts_start + duration);
-        len = snprintf(header, sizeof(header), "Dialogue: 0,%s,%s,",
+        len = snprintf(header, sizeof(header), "Dialogue: 0,%s,%s,Default,",
                        s_start, s_end);
     }
 

tests/ref/fate/sub-srt

-03b2a3f7e7e83624c8e4d1b5569df758
+a246a00ed72655cb8db3eaf64a522e0d