Expose threads in filter graph

av/filter/graph.py

@@ -27,6 +27,23 @@ def __dealloc__(self):
             # This frees the graph, filter contexts, links, etc..
             lib.avfilter_graph_free(cython.address(self.ptr))
 
+    @property
+    def threads(self):
+        """Maximum number of threads used by filters in this graph.
+
+        Set to 0 for automatic thread count. Must be set before adding any
+        filters to the graph.
+
+        Wraps :ffmpeg:`AVFilterGraph.nb_threads`.
+        """
+        return self.ptr.nb_threads
+
+    @threads.setter
+    def threads(self, value: cython.int):
+        if self.ptr.nb_filters:
+            raise RuntimeError("Cannot change threads after filters have been added.")
+        self.ptr.nb_threads = value
+
     @cython.cfunc
     def _get_unique_name(self, name: str) -> str:
         count = self._name_counts.get(name, 0)

av/filter/graph.pyi

@@ -14,6 +14,7 @@ from .filter import Filter
 
 class Graph:
     configured: bool
+    threads: int
 
     def __init__(self) -> None: ...
     def configure(self, auto_buffer: bool = True, force: bool = False) -> None: ...

include/avfilter.pxd

@@ -58,6 +58,7 @@ cdef extern from "libavfilter/avfilter.h" nogil:
     cdef struct AVFilterGraph:
         int nb_filters
         AVFilterContext **filters
+        int nb_threads
 
     cdef struct AVFilterInOut:
         char *name

tests/test_filters.py

@@ -193,11 +193,10 @@ def test_audio_buffer_volume_filter(self):
 
         assert np.allclose(input_data * 0.5, output_data)
 
-    def test_video_buffer(self):
+    def _test_video_buffer(self, graph):
         input_container = av.open(format="lavfi", file="color=c=pink:duration=1:r=30")
         input_video_stream = input_container.streams.video[0]
 
-        graph = av.filter.Graph()
         buffer = graph.add_buffer(template=input_video_stream)
         bwdif = graph.add("bwdif", "send_field:tff:all")
         buffersink = graph.add("buffersink")
@@ -223,6 +222,14 @@ def test_video_buffer(self):
                 assert filtered_frames[1].pts == (frame.pts - 1) * 2 + 1
                 assert filtered_frames[1].time_base == Fraction(1, 60)
 
+    def test_video_buffer(self):
+        self._test_video_buffer(av.filter.Graph())
+
+    def test_video_buffer_threading(self):
+        graph = av.filter.Graph()
+        graph.threads = 4
+        self._test_video_buffer(graph)
+
     def test_EOF(self) -> None:
         input_container = av.open(format="lavfi", file="color=c=pink:duration=1:r=30")
         video_stream = input_container.streams.video[0]
@@ -246,3 +253,15 @@ def test_EOF(self) -> None:
         assert isinstance(palette_frame, av.VideoFrame)
         assert palette_frame.width == 16
         assert palette_frame.height == 16
+
+    def test_graph_threads(self) -> None:
+        graph = Graph()
+        assert graph.threads == 0
+
+        graph.threads = 4
+        assert graph.threads == 4
+
+        graph.add("testsrc")
+
+        with self.assertRaises(RuntimeError):
+            graph.threads = 2