[FFmpeg-devel] [PATCH 2/2] avcodec/vc1: fix decoding of old WMV3 format

[Jerome Borsboom]

The position of the B MV predicitor candidate is slightly different
for the old WMV3 format that is indicated by RES_RTM_FLAG. This patch
fixes the decoding artifacts in the niceday.wmv sample.

Signed-off-by: Jerome Borsboom <jerome.borsboom at carpalis.nl>
---
 libavcodec/vc1.c      | 5 -----
 libavcodec/vc1_pred.c | 7 ++++++-
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/libavcodec/vc1.c b/libavcodec/vc1.c
index 3581d87b57..e102b931d8 100644
--- a/libavcodec/vc1.c
+++ b/libavcodec/vc1.c
@@ -379,11 +379,6 @@ int ff_vc1_decode_sequence_header(AVCodecContext *avctx, VC1Context *v, GetBitCo
     } else {
         v->res_rtm_flag = get_bits1(gb); //reserved
     }
-    if (!v->res_rtm_flag) {
-        av_log(avctx, AV_LOG_ERROR,
-               "Old WMV3 version detected, some frames may be decoded incorrectly\n");
-        //return -1;
-    }
     //TODO: figure out what they mean (always 0x402F)
     if (!v->res_fasttx)
         skip_bits(gb, 16);
diff --git a/libavcodec/vc1_pred.c b/libavcodec/vc1_pred.c
index 0b22d9916c..1ae1e33fbe 100644
--- a/libavcodec/vc1_pred.c
+++ b/libavcodec/vc1_pred.c
@@ -275,7 +275,12 @@ void ff_vc1_pred_mv(VC1Context *v, int n, int dmv_x, int dmv_y,
         //in 4-MV mode different blocks have different B predictor position
         switch (n) {
         case 0:
-            off = (s->mb_x > 0) ? -1 : 1;
+            if (v->res_rtm_flag)
+                off = s->mb_x ? -1 : 1;
+            else {
+                off = s->mb_x ? -1 : 2 * s->mb_width - wrap - 1;
+                b_valid = b_valid && (s->mb_x || s->mb_y > 1);
+            }
             break;
         case 1:
             off = (s->mb_x == (s->mb_width - 1)) ? -1 : 1;
-- 
2.13.6