filters: lavfi: allow hwdec_interop selection for filters

Today, lavfi filters are provided a hw_device from the first
hwdec_interop that was loaded, regardless of whether it's the right one
or not. In most situations where a hardware based filter is used, we
need more control over the device.

In this change, a `hwdec_interop` option is added to the lavfi wrapper
filter configuration and this is used to pick the correct hw_device to
inject into the filter or graph (in the case of a graph, all filters
get the same device).

Note that this requires the use of the explicit lavfi syntax to allow
for the extra configuration.

eg:

```
mpv --vf=hwupload
```

becomes

```
mpv --vf=lavfi=[hwupload]:hwdec_interop=cuda-nvdec
```

or

```
mpv --vf=lavfi-bridge=[hwupload]:hwdec_interop=cuda-nvdec
```

1 files changed, 1 insertions, 1 deletions

diff --git a/filters/user_filters.c b/filters/user_filters.c
index 34382ba052..cf1764e9c9 100644
--- a/filters/user_filters.c
+++ b/filters/user_filters.c
@@ -155,7 +155,7 @@ struct mp_filter *mp_create_user_filter(struct mp_filter *parent,
         if (strncmp(name, "lavfi-", 6) == 0)
             name += 6;
         struct mp_lavfi *l =
-            mp_lavfi_create_filter(parent, frame_type, true, NULL, name, args);
+            mp_lavfi_create_filter(parent, frame_type, true, NULL, NULL, name, args);
         if (l)
             f = l->f;
         goto done;