lavc/vp6: Implement "slice" threading for VP6A decode

The YUV channels of VP6 are encoded in a highly linear fashion which does
not have any slice-like concept to thread.  The alpha channel of VP6A is
fairly independent of the YUV and comprises 40% of the work.  This patch
uses the THREAD_SLICE capability to split the YUV and A decodes into
separate threads.

Two bugs are fixed by splitting YUV and alpha state:
- qscale_table from VP6A decode was for alpha channel instead of YUV
- alpha channel filtering settings were overwritten by YUV header parse

Signed-off-by: Ben Jackson <ben@ben.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

1 files changed, 4 insertions, 1 deletions

diff --git a/libavcodec/vp56.h b/libavcodec/vp56.h
index 7a32342..44bd229 100644
--- a/libavcodec/vp56.h
+++ b/libavcodec/vp56.h
@@ -161,8 +161,11 @@ struct vp56_context {
     VP56ParseCoeffModels parse_coeff_models;
     VP56ParseHeader parse_header;
 
+    /* for "slice" parallelism between YUV and A */
+    VP56Context *alpha_context;
+
     VP56Model *modelp;
-    VP56Model models[2];
+    VP56Model model;
 
     /* huffman decoding */
     int use_huffman;