avcodec/movtextdec: Fix immediately adjacent styles

The checks for whether a style should be opened/closed at the current
character position are as follows: A variable entry contained the index
of the currently active or potentially next active style. If the current
character position coincided with the start of style[entry], the style
was activated; this was followed by a check whether the current
character position coincided with the end of style[entry]; if so, the
style was deactivated and entry incremented. Afterwards the char was
processed.

The order of the checks leads to problems in case the endChar of style A
coincides with the startChar of the next style (say B): Style B was never
opened. When we are at said common position, the currently active style
is A and so the start pos check does not succeed; but the end pos check
does and it closes the currently active style A and increments entry.
At the next iteration of the loop, the current character position is
bigger than the start position of style B (which is style[entry]) and
therefore the style is not activated.

The solution is of course to first check for whether a style needs to be
closed (and increment entry if it does) before checking whether the next
style needs to be opened.

Reviewed-by: Philip Langdale <philipl@overt.org>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

1 files changed, 10 insertions, 9 deletions

diff --git a/libavcodec/movtextdec.c b/libavcodec/movtextdec.c
index d167eddea5..d46d64b6f2 100644
--- a/libavcodec/movtextdec.c
+++ b/libavcodec/movtextdec.c
@@ -373,7 +373,16 @@ static int text_to_ass(AVBPrint *buf, const char *text, const char *text_end,
 
         if ((m->box_flags & STYL_BOX) && entry < m->style_entries) {
             const StyleBox *style = &m->s[entry];
-            if (text_pos == style->style_start) {
+            if (text_pos == style->style_end) {
+                if (style_active) {
+                    av_bprintf(buf, "{\\r}");
+                    style_active = 0;
+                    color = m->d.color;
+                }
+                entry++;
+                style++;
+            }
+            if (entry < m->style_entries && text_pos == style->style_start) {
                 style_active = 1;
                 if (style->bold ^ m->d.bold)
                     av_bprintf(buf, "{\\b%d}", style->bold);
@@ -395,14 +404,6 @@ static int text_to_ass(AVBPrint *buf, const char *text, const char *text_end,
                 if (m->d.alpha != style->alpha)
                     av_bprintf(buf, "{\\1a&H%02X&}", 255 - style->alpha);
             }
-            if (text_pos == style->style_end) {
-                if (style_active) {
-                    av_bprintf(buf, "{\\r}");
-                    style_active = 0;
-                    color = m->d.color;
-                }
-                entry++;
-            }
         }
         if (m->box_flags & HLIT_BOX) {
             if (text_pos == m->h.hlit_start) {