lib/ffmpeg/Filter: add ParseSingleInOut()

Merge some duplicate code.

src/filter/plugins/FfmpegFilterPlugin.cxx

@@ -47,17 +47,7 @@ PreparedFfmpegFilter::Open(AudioFormat &in_audio_format)
 
 	auto &buffer_sink = Ffmpeg::MakeAudioBufferSink(*graph);
 
-	Ffmpeg::FilterInOut io_sink("out", buffer_sink);
+	graph.ParseSingleInOut(graph_string, buffer_sink, buffer_src);
-	Ffmpeg::FilterInOut io_src("in", buffer_src);
-	auto io = graph.Parse(graph_string, std::move(io_sink),
-			      std::move(io_src));
-
-	if (io.first.get() != nullptr)
-		throw std::runtime_error("FFmpeg filter has an open input");
-
-	if (io.second.get() != nullptr)
-		throw std::runtime_error("FFmpeg filter has an open output");
-
 	graph.CheckAndConfigure();
 
 	const auto out_audio_format =

src/filter/plugins/HdcdFilterPlugin.cxx

@@ -48,18 +48,7 @@ OpenHdcdFilter(AudioFormat &in_audio_format)
 
 	auto &buffer_sink = Ffmpeg::MakeAudioBufferSink(*graph);
 
-	Ffmpeg::FilterInOut io_sink("out", buffer_sink);
+	graph.ParseSingleInOut(hdcd_graph, buffer_sink, buffer_src);
-	Ffmpeg::FilterInOut io_src("in", buffer_src);
-
-	auto io = graph.Parse(hdcd_graph, std::move(io_sink),
-			      std::move(io_src));
-
-	if (io.first.get() != nullptr)
-		throw std::runtime_error("FFmpeg filter has an open input");
-
-	if (io.second.get() != nullptr)
-		throw std::runtime_error("FFmpeg filter has an open output");
-
 	graph.CheckAndConfigure();
 
 	auto out_audio_format = in_audio_format;

src/lib/ffmpeg/Filter.cxx

@@ -100,4 +100,17 @@ MakeAudioBufferSink(AVFilterGraph &graph_ctx)
 			    graph_ctx);
 }
 
+void
+FilterGraph::ParseSingleInOut(const char *filters, AVFilterContext &in,
+			      AVFilterContext &out)
+{
+	auto [inputs, outputs] = Parse(filters, {"out", in}, {"in", out});
+
+	if (inputs.get() != nullptr)
+		throw std::runtime_error("FFmpeg filter has an open input");
+
+	if (outputs.get() != nullptr)
+		throw std::runtime_error("FFmpeg filter has an open output");
+}
+
 } // namespace Ffmpeg

src/lib/ffmpeg/Filter.hxx

@@ -138,6 +138,9 @@ public:
 		return std::make_pair(std::move(inputs), std::move(outputs));
 	}
 
+	void ParseSingleInOut(const char *filters, AVFilterContext &in,
+			      AVFilterContext &out);
+
 	std::pair<FilterInOut, FilterInOut> Parse(const char *filters) {
 		AVFilterInOut *inputs, *outputs;
 		int err = avfilter_graph_parse2(graph, filters,