h263_get_motion_length() forgot to take an absolute value;
as a consequence, a negative index was used to access an array.
This leads to potential crashes, but mostly it just accesses what
is to the left of ff_mvtab (unless one uses ASAN), thereby defeating
the purpose of the AV_CODEC_FLAG2_NO_OUTPUT because the sizes of
the returned packets differ from the sizes the encoder would actually
have produced.
Signed-off-by: Andreas Rheinhardt <andreas.rheinha...@outlook.com>
---
Do we need this AV_CODEC_FLAG2_NO_OUTPUT codepath in h263.h and
mpeg4videoenc.c at all? It seems to have never worked and the speed
difference to encoding with output is negligible. (And I have not even
investigated whether the checks for whether said flag is set impact
the performance of ordinary encoding.)
libavcodec/h263.h | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/libavcodec/h263.h b/libavcodec/h263.h
index 70fd1ffdc0..d6bef8318d 100644
--- a/libavcodec/h263.h
+++ b/libavcodec/h263.h
@@ -100,15 +100,16 @@ void ff_h263_encode_motion(PutBitContext *pb, int val,
int f_code);
static inline int h263_get_motion_length(int val, int f_code){
- int l, bit_size, code;
+ int bit_size, code, sign;
if (val == 0) {
return 1; /* ff_mvtab[0][1] */
} else {
bit_size = f_code - 1;
/* modulo encoding */
- l= INT_BIT - 6 - bit_size;
- val = (val<<l)>>l;
+ val = sign_extend(val, 6 + bit_size);
+ sign = val >> 31;
+ val = (val ^ sign) - sign; /* val = FFABS(val) */
val--;
code = (val >> bit_size) + 1;
--
2.30.2
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