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, 2 deletions

diff --git a/filters/filter.h b/filters/filter.h
index 52797eb433..4df54b6112 100644
--- a/filters/filter.h
+++ b/filters/filter.h
@@ -408,8 +408,7 @@ struct mp_stream_info {
 // Search for a parent filter (including f) that has this set, and return it.
 struct mp_stream_info *mp_filter_find_stream_info(struct mp_filter *f);
 
-struct AVBufferRef;
-struct AVBufferRef *mp_filter_load_hwdec_device(struct mp_filter *f, int imgfmt);
+struct mp_hwdec_ctx *mp_filter_load_hwdec_device(struct mp_filter *f, int imgfmt);
 
 // Perform filtering. This runs until the filter graph is blocked (due to
 // missing external input or unread output). It returns whether any outside