[FFmpeg-devel] [PATCH v3] avcodec/h264_mb: Fix tmp buffer overlap in mc_part_weighted

[Bin Peng]

When decoding a bitstream with weighted-bipred enabled,
the results on ARM and x86 platforms may differ.

The reason for the inconsistency is that the value of
STRIDE_ALIGN differs between platforms. And STRIDE_ALIGN
is set to the buffer stride of temporary buffers for U
and V components in mc_part_weighted.

If the buffer stride is 32 or 64 (as on x86 platforms),
the U and V pixels can be interleaved row by row without
overlapping, resulting in correct output.
However, on ARM platforms where the stride is 16,
the V component will overwrite part of the U component's pixels,
leading to incorrect predicted pixels.

Fixes: ticket 11357

Signed-off-by: Bin Peng <pengbin at visionular.com>
---
 libavcodec/h264_mb.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/libavcodec/h264_mb.c b/libavcodec/h264_mb.c
index 4e94136313..b480cd312b 100644
--- a/libavcodec/h264_mb.c
+++ b/libavcodec/h264_mb.c
@@ -407,8 +407,8 @@ static av_always_inline void mc_part_weighted(const H264Context *h, H264SliceCon
         /* don't optimize for luma-only case, since B-frames usually
          * use implicit weights => chroma too. */
         uint8_t *tmp_cb = sl->bipred_scratchpad;
-        uint8_t *tmp_cr = sl->bipred_scratchpad + (16 << pixel_shift);
-        uint8_t *tmp_y  = sl->bipred_scratchpad + 16 * sl->mb_uvlinesize;
+        uint8_t *tmp_cr = sl->bipred_scratchpad + (16 * sl->mb_uvlinesize);
+        uint8_t *tmp_y  = sl->bipred_scratchpad + (32 * sl->mb_uvlinesize);
         int refn0       = sl->ref_cache[0][scan8[n]];
         int refn1       = sl->ref_cache[1][scan8[n]];
 
-- 
2.25.1