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[FFmpeg-devel,06/11] avcodec/movtextdec: Skip empty styles

Message ID 20201017182248.577108-6-andreas.rheinhardt@gmail.com
State Accepted
Commit 40c16907bb69da6318917bbceac06f8325d361b6
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Series [FFmpeg-devel,01/11] avcodec/movtextdec: Reset counter of fonts when freeing them
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Commit Message

Andreas Rheinhardt Oct. 17, 2020, 6:22 p.m. UTC
They would either lead to unnecessary ASS tags being emitted (namely
tags that are reset immediately thereafter) or would lead to problems
when parsing: e.g. if a zero-length style immediately follows another
style, the current code will end the preceding style and set the
zero-length style as the next potentially active style, but it is only
tested for activation when the next character is parsed at which point
the current offset is already greater than both the starting as well
as the end offset of the empty style. It will therefore neither be
opened nor closed and all subsequent styles will be ignored.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
---
 libavcodec/movtextdec.c | 8 ++++++++
 1 file changed, 8 insertions(+)
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Patch

diff --git a/libavcodec/movtextdec.c b/libavcodec/movtextdec.c
index e9df979e92..d167eddea5 100644
--- a/libavcodec/movtextdec.c
+++ b/libavcodec/movtextdec.c
@@ -302,6 +302,14 @@  static int decode_styl(const uint8_t *tsmb, MovTextContext *m, AVPacket *avpkt)
         }
 
         tsmb += 2;
+        if (style->style_start == style->style_end) {
+            /* Skip this style as it applies to no character */
+            tsmb += 8;
+            m->style_entries--;
+            i--;
+            continue;
+        }
+
         style->style_fontID = AV_RB16(tsmb);
         tsmb += 2;
         style->style_flag = AV_RB8(tsmb);