[FFmpeg-devel] [PATCH] avcodec/h264_mb: Fix buffer stride for arm

[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.

The bug can be reproduced by the following bitstream.

https://trac.ffmpeg.org/attachment/ticket/11357/inter_weighted_bipred2.264

And the ref/fate file is also added in this patch.

Fixes: ticket 11357
Signed-off-by: Bin Peng <pengbin at visionular.com>
---
 libavcodec/utils.c                            |  4 ++-
 .../h264-conformance-weighted_bipred2.264     | 31 +++++++++++++++++++
 2 files changed, 34 insertions(+), 1 deletion(-)
 create mode 100644 tests/ref/fate/h264-conformance-weighted_bipred2.264

diff --git a/libavcodec/utils.c b/libavcodec/utils.c
index 90867ed6b1..5d15f5c8fa 100644
--- a/libavcodec/utils.c
+++ b/libavcodec/utils.c
@@ -144,6 +144,7 @@ void avcodec_align_dimensions2(AVCodecContext *s, int *width, int *height,
     int i;
     int w_align = 1;
     int h_align = 1;
+    int stride_align = STRIDE_ALIGN;
     AVPixFmtDescriptor const *desc = av_pix_fmt_desc_get(s->pix_fmt);
 
     if (desc) {
@@ -339,13 +340,14 @@ void avcodec_align_dimensions2(AVCodecContext *s, int *width, int *height,
         // increasing witdth ensure that the temporary area is large enough,
         // the next rounded up width is 32
         *width = FFMAX(*width, 32);
+        stride_align = FFMAX(stride_align, 32);
     }
     if (s->codec_id == AV_CODEC_ID_SVQ3) {
         *width = FFMAX(*width, 32);
     }
 
     for (i = 0; i < 4; i++)
-        linesize_align[i] = STRIDE_ALIGN;
+        linesize_align[i] = stride_align;
 }
 
 void avcodec_align_dimensions(AVCodecContext *s, int *width, int *height)
diff --git a/tests/ref/fate/h264-conformance-weighted_bipred2.264 b/tests/ref/fate/h264-conformance-weighted_bipred2.264
new file mode 100644
index 0000000000..1d9bf90d12
--- /dev/null
+++ b/tests/ref/fate/h264-conformance-weighted_bipred2.264
@@ -0,0 +1,31 @@
+#software: Lavf61.1.100
+#tb 0: 1/24
+#media_type 0: video
+#codec_id 0: rawvideo
+#dimensions 0: 32x168
+#sar 0: 0/1
+0,          0,          0,        2,     8064, 0x836abac1
+0,          2,          2,        2,     8064, 0x836abac1
+0,          4,          4,        2,     8064, 0x836abac1
+0,          6,          6,        2,     8064, 0x836abac1
+0,          8,          8,        2,     8064, 0x836abac1
+0,         10,         10,        2,     8064, 0x5fc56e41
+0,         12,         12,        2,     8064, 0x5fc56e41
+0,         14,         14,        2,     8064, 0x5fc56e41
+0,         16,         16,        2,     8064, 0x5fc56e41
+0,         18,         18,        2,     8064, 0x5fc56e41
+0,         20,         20,        2,     8064, 0xbfbb8282
+0,         22,         22,        2,     8064, 0xbfbb8282
+0,         24,         24,        2,     8064, 0x4cbc7d64
+0,         26,         26,        2,     8064, 0x5eaf7bd3
+0,         28,         28,        2,     8064, 0x43956bb8
+0,         30,         30,        2,     8064, 0x047a0f2d
+0,         32,         32,        2,     8064, 0x0d271111
+0,         34,         34,        2,     8064, 0xab421086
+0,         36,         36,        2,     8064, 0x00780fcb
+0,         38,         38,        2,     8064, 0xfd2513c0
+0,         40,         40,        2,     8064, 0xa10b5ae7
+0,         42,         42,        2,     8064, 0xa10b5ae7
+0,         44,         44,        2,     8064, 0xa10b5ae7
+0,         46,         46,        2,     8064, 0xa10b5ae7
+0,         48,         48,        2,     8064, 0xa10b5ae7
-- 
2.25.1