From 40c16907bb69da6318917bbceac06f8325d361b6 Mon Sep 17 00:00:00 2001 From: Andreas Rheinhardt Date: Sat, 17 Oct 2020 17:48:54 +0200 Subject: [PATCH] avcodec/movtextdec: Skip empty styles 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. Reviewed-by: Philip Langdale Signed-off-by: Andreas Rheinhardt --- libavcodec/movtextdec.c | 8 ++++++++ 1 file changed, 8 insertions(+) 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);