f_lavfi: don't reject dynamic lavfi ins/outs

Ideally, users should be using lavfi-complex instead of lavfi-bridge
for such a use case, however currently lavfi-complex doesn't support
hwdec. So we can allow filters with dynamic inputs to work with
lavfi-bridge, at the cost of them only being able to take in
only one input. This should probably be reverted when/if lavfi-complex
has hwdec, but for now this allows us to use libplacebo
as a video filter with hwdec in mpv again.

1 files changed, 6 insertions, 0 deletions

diff --git a/DOCS/man/vf.rst b/DOCS/man/vf.rst
index bd3254e557..d42acdc44b 100644
--- a/DOCS/man/vf.rst
+++ b/DOCS/man/vf.rst
@@ -44,6 +44,12 @@ The exact syntax is:
     the ``lavfi`` filter, which uses a very similar syntax as mpv (MPlayer
     historically) to specify filters and their parameters.
 
+.. note::
+
+    ``--vf`` can only take a single track as input, even if the filter supports
+    dynamic input. Filters that require multiple inputs can't be used.
+    Use ``--lavfi-complex`` for such a use case. This also applies for ``--af``.
+
 Filters can be manipulated at run time. You can use ``@`` labels as described
 above in combination with the ``vf`` command (see `COMMAND INTERFACE`_) to get
 more control over this. Initially disabled filters with ``!`` are useful for