avcodec: disable frame multithreading with dxva2

Fix #11930, #11693

modules/codec/avcodec/video.c

@@ -347,6 +347,21 @@ int InitVideoDec( decoder_t *p_dec, AVCodecContext *p_context,
 # endif
     }
 
+    /* Workaround: frame multithreading is not compatible with
+     * DXVA2. When a frame is being copied to host memory, the frame
+     * is locked and cannot be used as a reference frame
+     * simultaneously and thus decoding fails for some frames. This
+     * causes major image corruption. */
+# if defined(_WIN32)
+    char *avcodec_hw = var_InheritString( p_dec, "avcodec-hw" );
+    if( avcodec_hw == NULL || strcasecmp( avcodec_hw, "none" ) )
+    {
+        msg_Warn( p_dec, "threaded frame decoding is not compatible with DXVA2, disabled" );
+        p_sys->p_context->thread_type &= ~FF_THREAD_FRAME;
+    }
+    free( avcodec_hw );
+# endif
+
     if( p_sys->p_context->thread_type & FF_THREAD_FRAME )
         p_dec->i_extra_picture_buffers = 2 * p_sys->p_context->thread_count;
 #endif