diff --git a/linuxpy/types.py b/linuxpy/types.py
index 690ed8b..34e9e00 100644
--- a/linuxpy/types.py
+++ b/linuxpy/types.py
@@ -25,9 +25,11 @@
 
 
 Union = typing.Union
+Optional = typing.Optional
 PathLike = Union[str, pathlib.Path, os.PathLike]
 
 Iterable = collections.abc.Iterable
 Iterator = collections.abc.Iterator
 AsyncIterable = collections.abc.AsyncIterable
 AsyncIterator = collections.abc.AsyncIterator
+Callable = collections.abc.Callable
diff --git a/linuxpy/video/device.py b/linuxpy/video/device.py
index d8af662..b610d7c 100644
--- a/linuxpy/video/device.py
+++ b/linuxpy/video/device.py
@@ -27,7 +27,7 @@
 )
 from linuxpy.io import IO
 from linuxpy.ioctl import ioctl
-from linuxpy.types import AsyncIterator, Buffer, Iterable, Iterator, PathLike, Self
+from linuxpy.types import AsyncIterator, Buffer, Callable, Iterable, Iterator, Optional, PathLike, Self
 
 from . import raw
 
@@ -1110,7 +1110,7 @@ def __init__(self, device: Device, buffer_type: BufferType, size: int = 2):
         self.buffers = None
         self.name = type(self).__name__
 
-    def formats(self):
+    def formats(self) -> list:
         formats = self.device.info.formats
         return [fmt for fmt in formats if fmt.type == self.type]
 
@@ -1515,7 +1515,7 @@ async def aread(self):
 
 
 class FrameReader:
-    def __init__(self, device: Device, raw_read, max_queue_size=1):
+    def __init__(self, device: Device, raw_read: Callable[[], Buffer], max_queue_size: int = 1):
         self.device = device
         self.raw_read = raw_read
         self._loop = None
@@ -1524,7 +1524,7 @@ def __init__(self, device: Device, raw_read, max_queue_size=1):
         self._max_queue_size = max_queue_size
         self._device_fd = None
 
-    async def __aenter__(self):
+    async def __aenter__(self) -> Self:
         if self.device.is_blocking:
             raise V4L2Error("Cannot use async frame reader on blocking device")
         self._device_fd = self.device.fileno()
@@ -1547,13 +1547,13 @@ async def __aexit__(self, exc_type, exc_value, traceback):
         self._loop = None
         self._buffer = None
 
-    def __enter__(self):
+    def __enter__(self) -> Self:
         return self
 
     def __exit__(self, exc_type, exc_value, tb):
         pass
 
-    def _on_event(self):
+    def _on_event(self) -> None:
         task = self._loop.create_future()
         try:
             self._selector.poll(0)  # avoid blocking
@@ -1568,14 +1568,14 @@ def _on_event(self):
             buffer.get_nowait()
         buffer.put_nowait(task)
 
-    def read(self, timeout=None):
+    def read(self, timeout: Optional[float] = None) -> Frame:
         if not self.device.is_blocking:
             read, _, _ = self.device.io.select((self.device,), (), (), timeout)
             if not read:
                 return
         return self.raw_read()
 
-    async def aread(self):
+    async def aread(self) -> Frame:
         """Wait for next frame or return last frame"""
         task = await self._buffer.get()
         return await task
@@ -1609,18 +1609,18 @@ def __init__(self, buffer_manager: BufferManager):
     def device(self) -> Device:
         return self.buffer_manager.device
 
-    def raw_write(self, data):
+    def raw_write(self, data: Buffer) -> None:
         self.device.write(data)
 
-    def wait_write(self, data):
+    def wait_write(self, data: Buffer) -> None:
         device = self.device
         if device.io.select is not None:
             _, w, _ = device.io.select((), (device,), ())
         if not w:
             raise OSError("Closed")
-        return self.raw_write(data)
+        self.raw_write(data)
 
-    def write(self, data: bytes):
+    def write(self, data: Buffer) -> None:
         # first time we check what mode device was opened (blocking vs non-blocking)
         # if file was opened with O_NONBLOCK: DQBUF will not block until a buffer
         # is available for write. So we need to do it here
@@ -1630,10 +1630,10 @@ def write(self, data: bytes):
             self.write = self.wait_write
         return self.write(data)
 
-    def open(self):
+    def open(self) -> None:
         pass
 
-    def close(self):
+    def close(self) -> None:
         pass
 
 
@@ -1680,7 +1680,7 @@ def close(self) -> None:
             self.buffer = None
             self.device.log.info("Video output closed")
 
-    def write(self, data: Buffer):
+    def write(self, data: Buffer) -> None:
         self.buffer.write(data)