diff --git a/libavcodec/movtextdec.c b/libavcodec/movtextdec.c
index 7b5b161..4cffacf 100644
--- a/libavcodec/movtextdec.c
+++ b/libavcodec/movtextdec.c
@@ -328,6 +328,7 @@ static int text_to_ass(AVBPrint *buf, const char *text, const char *text_end,
     int i = 0;
     int j = 0;
     int text_pos = 0;
+    int text_pos_chars = 0;
 
     if (text < text_end && m->box_flags & TWRP_BOX) {
         if (m->w.wrap_flag == 1) {
@@ -338,50 +339,59 @@ static int text_to_ass(AVBPrint *buf, const char *text, const char *text_end,
     }
 
     while (text < text_end) {
-        if (m->box_flags & STYL_BOX) {
-            for (i = 0; i < m->style_entries; i++) {
-                if (m->s[i]->style_flag && text_pos == m->s[i]->style_end) {
-                    av_bprintf(buf, "{\\r}");
+        if ((*text & 0xC0) != 0x80) { // Boxes never split multibyte characters
+            if (m->box_flags & STYL_BOX) {
+                for (i = 0; i < m->style_entries; i++) {
+                    if (m->s[i]->style_flag &&
+                        text_pos_chars == m->s[i]->style_end)
+                    {
+                        av_bprintf(buf, "{\\r}");
+                    }
                 }
-            }
-            for (i = 0; i < m->style_entries; i++) {
-                if (m->s[i]->style_flag && text_pos == m->s[i]->style_start) {
-                    if (m->s[i]->style_flag & STYLE_FLAG_BOLD)
-                        av_bprintf(buf, "{\\b1}");
-                    if (m->s[i]->style_flag & STYLE_FLAG_ITALIC)
-                        av_bprintf(buf, "{\\i1}");
-                    if (m->s[i]->style_flag & STYLE_FLAG_UNDERLINE)
-                        av_bprintf(buf, "{\\u1}");
-                    av_bprintf(buf, "{\\fs%d}", m->s[i]->fontsize);
-                    for (j = 0; j < m->ftab_entries; j++) {
-                        if (m->s[i]->style_fontID == m->ftab[j]->fontID)
-                            av_bprintf(buf, "{\\fn%s}", m->ftab[j]->font);
+                for (i = 0; i < m->style_entries; i++) {
+                    if (m->s[i]->style_flag
+                        && text_pos_chars == m->s[i]->style_start)
+                    {
+                        if (m->s[i]->style_flag & STYLE_FLAG_BOLD)
+                            av_bprintf(buf, "{\\b1}");
+                        if (m->s[i]->style_flag & STYLE_FLAG_ITALIC)
+                            av_bprintf(buf, "{\\i1}");
+                        if (m->s[i]->style_flag & STYLE_FLAG_UNDERLINE)
+                            av_bprintf(buf, "{\\u1}");
+                        /* (No need to print font style if equal to default?) */
+                        av_bprintf(buf, "{\\fs%d}", m->s[i]->fontsize);
+                        for (j = 0; j < m->ftab_entries; j++) {
+                            if (m->s[i]->style_fontID == m->ftab[j]->fontID)
+                                av_bprintf(buf, "{\\fn%s}", m->ftab[j]->font);
+                        }
                     }
                 }
             }
-        }
-        if (m->box_flags & HLIT_BOX) {
-            if (text_pos == m->h.hlit_start) {
-                /* If hclr box is present, set the secondary color to the color
-                 * specified. Otherwise, set primary color to white and secondary
-                 * color to black. These colors will come from TextSampleModifier
-                 * boxes in future and inverse video technique for highlight will
-                 * be implemented.
-                 */
-                if (m->box_flags & HCLR_BOX) {
-                    av_bprintf(buf, "{\\2c&H%02x%02x%02x&}", m->c.hlit_color[2],
-                                m->c.hlit_color[1], m->c.hlit_color[0]);
-                } else {
-                    av_bprintf(buf, "{\\1c&H000000&}{\\2c&HFFFFFF&}");
+            if (m->box_flags & HLIT_BOX) {
+                if (text_pos_chars == m->h.hlit_start) {
+                    /* If hclr box is present, set the secondary color to the
+                     * color specified. Otherwise, set primary color to white
+                     * and secondary color to black. These colors will come from
+                     * TextSampleModifier boxes in future and inverse video
+                     * technique for highlight will be implemented.
+                     */
+                    if (m->box_flags & HCLR_BOX) {
+                        av_bprintf(buf, "{\\2c&H%02x%02x%02x&}",
+                                    m->c.hlit_color[2], m->c.hlit_color[1],
+                                    m->c.hlit_color[0]);
+                    } else {
+                        av_bprintf(buf, "{\\1c&H000000&}{\\2c&HFFFFFF&}");
+                    }
                 }
-            }
-            if (text_pos == m->h.hlit_end) {
-                if (m->box_flags & HCLR_BOX) {
-                    av_bprintf(buf, "{\\2c&H000000&}");
-                } else {
-                    av_bprintf(buf, "{\\1c&HFFFFFF&}{\\2c&H000000&}");
+                if (text_pos_chars == m->h.hlit_end) {
+                    if (m->box_flags & HCLR_BOX) {
+                        av_bprintf(buf, "{\\2c&H000000&}");
+                    } else {
+                        av_bprintf(buf, "{\\1c&HFFFFFF&}{\\2c&H000000&}");
+                    }
                 }
             }
+        text_pos_chars++;
         }
 
         switch (*text) {
@@ -412,10 +422,10 @@ static int mov_text_init(AVCodecContext *avctx) {
     MovTextContext *m = avctx->priv_data;
     ret = mov_text_tx3g(avctx, m);
     if (ret == 0) {
-        return ff_ass_subtitle_header(avctx, m->d.font, m->d.fontsize, m->d.color,
-                                m->d.back_color, m->d.bold, m->d.italic,
-                                m->d.underline, ASS_DEFAULT_BORDERSTYLE,
-                                m->d.alignment);
+        return ff_ass_subtitle_header(avctx, m->d.font, m->d.fontsize,
+                                m->d.color, m->d.back_color, m->d.bold,
+                                m->d.italic, m->d.underline,
+                                ASS_DEFAULT_BORDERSTYLE, m->d.alignment);
     } else
         return ff_ass_subtitle_header_default(avctx);
 }
@@ -491,7 +501,8 @@ static int mov_text_decode_frame(AVCodecContext *avctx,
 
             for (size_t i = 0; i < box_count; i++) {
                 if (tsmb_type == box_types[i].type) {
-                    if (m->tracksize + m->size_var + box_types[i].base_size > avpkt->size)
+                    if (m->tracksize + m->size_var +
+                        box_types[i].base_size > avpkt->size)
                         break;
                     ret_tsmb = box_types[i].decode(tsmb, m, avpkt);
                     if (ret_tsmb == -1)
