Module: libav
Branch: release/9
Commit: f4773e5b37875e3c261540857bf2fb90327fc6aa
Author: Anton Khirnov <an...@khirnov.net>
Committer: Sean McGovern <gsean...@gmail.com>
Date: Sat Dec 17 17:04:55 2016 +0100
mpeg12: move setting first_field to mpeg_field_start()
For field picture, the first_field is set based on its previous value.
Before this commit, first_field is set when reading the picture
coding extension. However, in corrupted files there may be multiple
picture coding extension headers, so the final value of first_field that
is actually used during decoding can be wrong. That can lead to various
undefined behaviour, like predicting from a non-existing field.
Fix this problem, by setting first_field in mpeg_field_start(), which
should be called exactly once per field.
CC: libav-sta...@libav.org
Bug-ID: 999
(cherry picked from commit c2fa6bb0e8703a7a6aa10e11f9ab36094416d83f)
Signed-off-by: Sean McGovern <gsean...@gmail.com>
---
libavcodec/mpeg12.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/libavcodec/mpeg12.c b/libavcodec/mpeg12.c
index a49828e..a0a68e7 100644
--- a/libavcodec/mpeg12.c
+++ b/libavcodec/mpeg12.c
@@ -1546,10 +1546,8 @@ static void
mpeg_decode_picture_coding_extension(Mpeg1Context *s1)
}
if (s->picture_structure == PICT_FRAME) {
- s->first_field = 0;
s->v_edge_pos = 16 * s->mb_height;
} else {
- s->first_field ^= 1;
s->v_edge_pos = 8 * s->mb_height;
memset(s->mbskip_table, 0, s->mb_stride * s->mb_height);
}
@@ -1579,6 +1577,11 @@ static int mpeg_field_start(MpegEncContext *s, const
uint8_t *buf, int buf_size)
AVCodecContext *avctx = s->avctx;
Mpeg1Context *s1 = (Mpeg1Context*)s;
+ if (s->picture_structure == PICT_FRAME)
+ s->first_field = 0;
+ else
+ s->first_field ^= 1;
+
/* start frame decoding */
if (s->first_field || s->picture_structure == PICT_FRAME) {
if (ff_MPV_frame_start(s, avctx) < 0)
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