diff --git a/av/filter/filter.pxd b/av/filter/filter.pxd
index 27501ae57..0a7cd41a0 100644
--- a/av/filter/filter.pxd
+++ b/av/filter/filter.pxd
@@ -4,9 +4,7 @@ from av.descriptor cimport Descriptor
 
 
 cdef class Filter:
-
     cdef const lib.AVFilter *ptr
-
     cdef object _inputs
     cdef object _outputs
     cdef Descriptor _descriptor
diff --git a/av/filter/filter.pyx b/av/filter/filter.py
similarity index 70%
rename from av/filter/filter.pyx
rename to av/filter/filter.py
index b6e7005f0..b348dd3e0 100644
--- a/av/filter/filter.pyx
+++ b/av/filter/filter.py
@@ -1,24 +1,26 @@
-cimport libav as lib
+import cython
+from cython.cimports import libav as lib
+from cython.cimports.av.descriptor import wrap_avclass
+from cython.cimports.av.filter.link import alloc_filter_pads
 
-from av.descriptor cimport wrap_avclass
-from av.filter.link cimport alloc_filter_pads
+_cinit_sentinel = cython.declare(object, object())
 
 
-cdef object _cinit_sentinel = object()
-
-
-cdef Filter wrap_filter(const lib.AVFilter *ptr):
-    cdef Filter filter_ = Filter(_cinit_sentinel)
+@cython.cfunc
+def wrap_filter(ptr: cython.pointer[cython.const[lib.AVFilter]]) -> Filter:
+    filter_: Filter = Filter(_cinit_sentinel)
     filter_.ptr = ptr
     return filter_
 
 
-cdef class Filter:
+@cython.cclass
+class Filter:
     def __cinit__(self, name):
         if name is _cinit_sentinel:
             return
         if not isinstance(name, str):
             raise TypeError("takes a filter name as a string")
+
         self.ptr = lib.avfilter_get_by_name(name)
         if not self.ptr:
             raise ValueError(f"no filter {name}")
@@ -60,19 +62,19 @@ def outputs(self):
         return self._outputs
 
 
-cdef get_filter_names():
-    names = set()
-    cdef const lib.AVFilter *ptr
-    cdef void *opaque = NULL
+@cython.cfunc
+def get_filter_names() -> set:
+    names: set = set()
+    ptr: cython.pointer[cython.const[lib.AVFilter]]
+    opaque: cython.p_void = cython.NULL
     while True:
-        ptr = lib.av_filter_iterate(&opaque)
+        ptr = lib.av_filter_iterate(cython.address(opaque))
         if ptr:
             names.add(ptr.name)
         else:
             break
     return names
 
-filters_available = get_filter_names()
-
 
+filters_available = get_filter_names()
 filter_descriptor = wrap_avclass(lib.avfilter_get_class())
diff --git a/av/utils.py b/av/utils.py
index 3516be0e3..bdf11bbb5 100644
--- a/av/utils.py
+++ b/av/utils.py
@@ -14,11 +14,6 @@ def _decode(s: cython.pointer[cython.char], encoding, errors) -> str:
     return cython.cast(bytes, s).decode(encoding, errors)
 
 
-@cython.cfunc
-def _encode(s, encoding, errors) -> bytes:
-    return s.encode(encoding, errors)
-
-
 @cython.cfunc
 def avdict_to_dict(
     input: cython.pointer[lib.AVDictionary], encoding: str, errors: str