class Stream(Generic[T]):
    def __init__(self, source: StreamSource[T]):
        self._source = source

    async def get_length(self) -> float:
        return await self._source.get_length()

    def slice(self, start=0, end=float('inf')):
        self._source = SliceSource(self._source, start, end)


class VideoStream(Stream[Frame]):
    def __init__(self, source: VideoSource):
        super().__init__(source)

        self._video_metadata_source = source

    async def get_resolution(self) -> Tuple[int, int]:
        return await self._video_metadata_source.get_resolution()

    def crop(self, x, y, w, h):
        self._source = self._video_metadata_source = CropSource(
            self._source,
            self._video_metadata_source,
            x, y, w, h,
        )