avfilter/hwmap: Set default BindFlags for reverse hw mapping to d3d11

When reverse mapping, hwmap creates a new hw frames context with default
parameters. In case of d3d11, the default for BindFlags is 0, for which
fixed-size pool allocation fails and for which textures are hardly
usable for anything in terms of video acceleration.

While the author would have preferred a solution in hwcontext_d3d11va,
the discussion ended up favoring this way.

See here: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/24046

Signed-off-by: softworkz <softworkz@hotmail.com>

libavfilter/vf_hwmap.c

@@ -22,6 +22,10 @@
 #include "libavutil/opt.h"
 #include "libavutil/pixdesc.h"
 
+#if CONFIG_D3D11VA
+#include "libavutil/hwcontext_d3d11va.h"
+#endif
+
 #include "avfilter.h"
 #include "filters.h"
 #include "formats.h"
@@ -151,6 +155,12 @@ static int hwmap_config_output(AVFilterLink *outlink)
             if (avctx->extra_hw_frames >= 0)
                 frames->initial_pool_size = 2 + avctx->extra_hw_frames;
 
+#if CONFIG_D3D11VA
+            if (frames->format == AV_PIX_FMT_D3D11) {
+                AVD3D11VAFramesContext *frames_d3d11 = frames->hwctx;
+                frames_d3d11->BindFlags = D3D11_BIND_DECODER | D3D11_BIND_SHADER_RESOURCE;
+            }
+#endif
             err = av_hwframe_ctx_init(ctx->hwframes_ref);
             if (err < 0) {
                 av_log(avctx, AV_LOG_ERROR, "Failed to initialise "