Fix filter graph crashes when linking or adding after configure

CHANGELOG.rst

@@ -39,6 +39,8 @@ Fixes:
 - ``Frame.time_base`` returns ``AVRational(0, 1)`` instead of ``None`` when unset, like other ``AVRational`` properties.
 - Fix type stubs that did not match runtime: ``average_rate``, ``base_rate``, and ``guessed_rate`` are only on ``VideoStream``; ``codec``, ``codec_tag``, and ``options`` are only on audio, video, and subtitle streams; ``Stream.codec_context`` may be ``None``; ``AudioStream.bit_rate``, ``InputContainer.start_time``, ``VideoFrame.time``, and ``FilterPad.context`` may be ``None``; ``Codec.hardware_configs`` is a tuple; ``CodecContext.delay`` is an ``int``; ``AudioStream.max_bit_rate`` is added; and the inaccessible ``Plane.frame``, ``Plane.index``, and ``Container.buffer_size`` are removed.
 - Fix more type stubs that did not match runtime: ``SubtitleSet`` items are ``AssSubtitle | BitmapSubtitle``; ``BitmapSubtitle`` supports ``len()``, iteration, and indexing; ``BitmapSubtitlePlane`` supports the buffer protocol; ``VideoFormat`` supports ``int()``; ``CodecContext.encode``, ``encode_lazy``, and ``decode`` have return types; ``SubtitleCodecContext.decode`` requires a packet; ``VideoStream.format`` may be ``None``; stream ``name`` is a ``str`` on audio, video, and subtitle streams; and ``VideoFrame.to_image``, ``set_image``, and ``from_image`` use ``PIL.Image.Image``.
+- ``FilterContext.link_to`` raises ``ValueError`` when linking filters from different graphs instead of aborting the process.
+- Filters added or linked after ``Graph.configure()`` are now configured on the next push or pull instead of segfaulting.
 
 v19.0.2
 -------

av/filter/context.py

@@ -96,7 +96,11 @@ def link_to(
         output_idx: cython.int = 0,
         input_idx: cython.int = 0,
     ):
+        # avfilter_link() aborts the process on a cross-graph link.
+        if input_.graph is not self.graph:
+            raise ValueError("cannot link filters from different graphs")
         err_check(lib.avfilter_link(self.ptr, output_idx, input_.ptr, input_idx))
+        self.graph.configured = False
 
     def push(self, frame: Frame | None):
         res: cython.int

av/filter/graph.py

@@ -126,6 +126,8 @@ def add(self, filter, args=None, **kwargs):
         ctx: FilterContext = wrap_filter_context(self, cy_filter, ptr)
         ctx.init(args, **kwargs)
         self._register_context(ctx)
+        # The new filter must be configured before it can push or pull.
+        self.configured = False
 
         # There might have been automatic contexts added (e.g. resamplers,
         # fifos, and scalers). It is more likely to see them after the graph

scripts/build-deps

@@ -83,7 +83,7 @@ echo ./configure
     --disable-bsfs \
     --enable-bsf=chomp,extract_extradata,h264_mp4toannexb,setts \
     --disable-filters \
-    --enable-filter=abuffer,abuffersink,aformat,aresample,atempo,buffer,buffersink,bwdif,color,ebur128,loudnorm,lutrgb,overlay,palettegen,scale,testsrc,vflip,volume \
+    --enable-filter=abuffer,abuffersink,aformat,aresample,atempo,buffer,buffersink,bwdif,color,ebur128,loudnorm,lutrgb,null,overlay,palettegen,scale,testsrc,vflip,volume \
     --disable-avx512 \
     $CONFFLAGS_NVIDIA \
     $CONFFLAGS_RISCV \

tests/test_filters.py

@@ -407,3 +407,64 @@ def test_graph_threads(self) -> None:
 
         with self.assertRaises(RuntimeError):
             graph.threads = 2
+
+    def test_link_across_graphs(self) -> None:
+        a = Graph().add("null")
+        b = Graph().add("null")
+
+        with pytest.raises(ValueError, match="different graphs"):
+            a.link_to(b)
+
+    def test_add_after_configure(self) -> None:
+        graph = Graph()
+        graph.configure()
+        assert graph.configured
+
+        src = graph.add_buffer(
+            width=64, height=64, format="rgb24", time_base=Fraction(1, 24)
+        )
+        sink = graph.add("buffersink")
+        assert not graph.configured
+        src.link_to(sink)
+
+        frame = VideoFrame(64, 64, "rgb24")
+        frame.pts = 0
+        src.push(frame)
+        assert graph.configured
+        out = sink.pull()
+        assert (out.width, out.height, out.pts) == (64, 64, 0)
+
+    def test_pull_unlinked_sink_after_configure(self) -> None:
+        graph = Graph()
+        graph.configure()
+        sink = graph.add("buffersink")
+
+        with pytest.raises(av.FFmpegError):
+            sink.pull()
+
+    def test_extend_running_graph(self) -> None:
+        graph = Graph()
+        src = graph.add_buffer(
+            width=32, height=32, format="rgb24", time_base=Fraction(1, 24)
+        )
+        sink = graph.add("buffersink")
+        src.link_to(sink)
+        frame = VideoFrame(32, 32, "rgb24")
+        frame.pts = 0
+        src.push(frame)
+        assert sink.pull().pts == 0
+
+        src2 = graph.add_buffer(
+            width=16, height=16, format="gray", time_base=Fraction(1, 24)
+        )
+        sink2 = graph.add("buffersink")
+        src2.link_to(sink2)
+        frame2 = VideoFrame(16, 16, "gray")
+        frame2.pts = 0
+        src2.push(frame2)
+        out = sink2.pull()
+        assert isinstance(out, VideoFrame) and out.format.name == "gray"
+
+        frame.pts = 1
+        src.push(frame)
+        assert sink.pull().pts == 1