lib/ffmpeg/Filter: eliminate class FilterContext

Since AVFilterContext are freed automatically, this wrapper class
serves no purpose.  Let's remove it.

src/filter/plugins/FfmpegFilter.cxx

@@ -32,12 +32,12 @@ extern "C" {
 FfmpegFilter::FfmpegFilter(const AudioFormat &in_audio_format,
 			   const AudioFormat &_out_audio_format,
 			   Ffmpeg::FilterGraph &&_graph,
-			   Ffmpeg::FilterContext &&_buffer_src,
+			   AVFilterContext &_buffer_src,
-			   Ffmpeg::FilterContext &&_buffer_sink) noexcept
+			   AVFilterContext &_buffer_sink) noexcept
 	:Filter(_out_audio_format),
 	 graph(std::move(_graph)),
-	 buffer_src(std::move(_buffer_src)),
+	 buffer_src(_buffer_src),
-	 buffer_sink(std::move(_buffer_sink)),
+	 buffer_sink(_buffer_sink),
 	 in_format(Ffmpeg::ToFfmpegSampleFormat(in_audio_format.format)),
 	 in_sample_rate(in_audio_format.sample_rate),
 	 in_channels(in_audio_format.channels),
@@ -61,7 +61,7 @@ FfmpegFilter::FilterPCM(ConstBuffer<void> src)
 
 	memcpy(frame.GetData(0), src.data, src.size);
 
-	int err = av_buffersrc_add_frame(buffer_src.get(), frame.get());
+	int err = av_buffersrc_add_frame(&buffer_src, frame.get());
 	if (err < 0)
 		throw MakeFfmpegError(err, "av_buffersrc_write_frame() failed");
 
@@ -69,7 +69,7 @@ FfmpegFilter::FilterPCM(ConstBuffer<void> src)
 
 	frame.Unref();
 
-	err = av_buffersink_get_frame(buffer_sink.get(), frame.get());
+	err = av_buffersink_get_frame(&buffer_sink, frame.get());
 	if (err < 0) {
 		if (err == AVERROR(EAGAIN) || err == AVERROR_EOF)
 			return nullptr;

src/filter/plugins/FfmpegFilter.hxx

@@ -30,7 +30,7 @@
  */
 class FfmpegFilter final : public Filter {
 	Ffmpeg::FilterGraph graph;
-	Ffmpeg::FilterContext buffer_src, buffer_sink;
+	AVFilterContext &buffer_src, &buffer_sink;
 	Ffmpeg::Frame frame;
 
 	FfmpegBuffer interleave_buffer;
@@ -51,8 +51,8 @@ public:
 	FfmpegFilter(const AudioFormat &in_audio_format,
 		     const AudioFormat &_out_audio_format,
 		     Ffmpeg::FilterGraph &&_graph,
-		     Ffmpeg::FilterContext &&_buffer_src,
+		     AVFilterContext &_buffer_src,
-		     Ffmpeg::FilterContext &&_buffer_sink) noexcept;
+		     AVFilterContext &_buffer_sink) noexcept;
 
 	/* virtual methods from class Filter */
 	ConstBuffer<void> FilterPCM(ConstBuffer<void> src) override;

src/filter/plugins/FfmpegFilterPlugin.cxx

@@ -42,14 +42,13 @@ PreparedFfmpegFilter::Open(AudioFormat &in_audio_format)
 {
 	Ffmpeg::FilterGraph graph;
 
-	auto buffer_src =
+	auto &buffer_src =
-		Ffmpeg::FilterContext::MakeAudioBufferSource(in_audio_format,
+		Ffmpeg::MakeAudioBufferSource(in_audio_format, *graph);
-							     *graph);
 
-	auto buffer_sink = Ffmpeg::FilterContext::MakeAudioBufferSink(*graph);
+	auto &buffer_sink = Ffmpeg::MakeAudioBufferSink(*graph);
 
-	Ffmpeg::FilterInOut io_sink("out", *buffer_sink);
+	Ffmpeg::FilterInOut io_sink("out", buffer_sink);
-	Ffmpeg::FilterInOut io_src("in", *buffer_src);
+	Ffmpeg::FilterInOut io_src("in", buffer_src);
 	auto io = graph.Parse(graph_string, std::move(io_sink),
 			      std::move(io_src));
 
@@ -62,14 +61,14 @@ PreparedFfmpegFilter::Open(AudioFormat &in_audio_format)
 	graph.CheckAndConfigure();
 
 	const auto out_audio_format =
-		Ffmpeg::DetectFilterOutputFormat(in_audio_format, *buffer_src,
+		Ffmpeg::DetectFilterOutputFormat(in_audio_format, buffer_src,
-						 *buffer_sink);
+						 buffer_sink);
 
 	return std::make_unique<FfmpegFilter>(in_audio_format,
 					      out_audio_format,
 					      std::move(graph),
-					      std::move(buffer_src),
+					      buffer_src,
-					      std::move(buffer_sink));
+					      buffer_sink);
 }
 
 static std::unique_ptr<PreparedFilter>

src/filter/plugins/HdcdFilterPlugin.cxx

@@ -42,14 +42,14 @@ OpenHdcdFilter(AudioFormat &in_audio_format)
 {
 	Ffmpeg::FilterGraph graph;
 
-	auto buffer_src =
+	auto &buffer_src =
-		Ffmpeg::FilterContext::MakeAudioBufferSource(in_audio_format,
+		Ffmpeg::MakeAudioBufferSource(in_audio_format,
-							     *graph);
+					      *graph);
 
-	auto buffer_sink = Ffmpeg::FilterContext::MakeAudioBufferSink(*graph);
+	auto &buffer_sink = Ffmpeg::MakeAudioBufferSink(*graph);
 
-	Ffmpeg::FilterInOut io_sink("out", *buffer_sink);
+	Ffmpeg::FilterInOut io_sink("out", buffer_sink);
-	Ffmpeg::FilterInOut io_src("in", *buffer_src);
+	Ffmpeg::FilterInOut io_src("in", buffer_src);
 
 	auto io = graph.Parse(hdcd_graph, std::move(io_sink),
 			      std::move(io_src));
@@ -69,8 +69,8 @@ OpenHdcdFilter(AudioFormat &in_audio_format)
 	return std::make_unique<FfmpegFilter>(in_audio_format,
 					      out_audio_format,
 					      std::move(graph),
-					      std::move(buffer_src),
+					      buffer_src,
-					      std::move(buffer_sink));
+					      buffer_sink);
 }
 
 class PreparedHdcdFilter final : public PreparedFilter {

src/lib/ffmpeg/Filter.cxx

@@ -39,9 +39,32 @@ RequireFilterByName(const char *name)
 	return *filter;
 }
 
-FilterContext
+static AVFilterContext &
-FilterContext::MakeAudioBufferSource(AudioFormat &audio_format,
+CreateFilter(const AVFilter &filt,
-				     AVFilterGraph &graph_ctx)
+	     const char *name, const char *args, void *opaque,
+	     AVFilterGraph &graph_ctx)
+{
+	AVFilterContext *context = nullptr;
+	int err = avfilter_graph_create_filter(&context, &filt,
+					       name, args, opaque,
+					       &graph_ctx);
+	if (err < 0)
+		throw MakeFfmpegError(err, "avfilter_graph_create_filter() failed");
+
+	return *context;
+}
+
+static AVFilterContext &
+CreateFilter(const AVFilter &filt,
+	     const char *name,
+	     AVFilterGraph &graph_ctx)
+{
+	return CreateFilter(filt, name, nullptr, nullptr, graph_ctx);
+}
+
+AVFilterContext &
+MakeAudioBufferSource(AudioFormat &audio_format,
+		      AVFilterGraph &graph_ctx)
 {
 	AVSampleFormat src_format = ToFfmpegSampleFormat(audio_format.format);
 	if (src_format == AV_SAMPLE_FMT_NONE) {
@@ -66,13 +89,15 @@ FilterContext::MakeAudioBufferSource(AudioFormat &audio_format,
 		ToFfmpegChannelLayout(audio_format.channels),
 		audio_format.sample_rate);
 
-	return {RequireFilterByName("abuffer"), "abuffer", abuffer_args, nullptr, graph_ctx};
+	return CreateFilter(RequireFilterByName("abuffer"), "abuffer",
+			    abuffer_args, nullptr, graph_ctx);
 }
 
-FilterContext
+AVFilterContext &
-FilterContext::MakeAudioBufferSink(AVFilterGraph &graph_ctx)
+MakeAudioBufferSink(AVFilterGraph &graph_ctx)
 {
-	return {RequireFilterByName("abuffersink"), "abuffersink", graph_ctx};
+	return CreateFilter(RequireFilterByName("abuffersink"), "abuffersink",
+			    graph_ctx);
 }
 
 } // namespace Ffmpeg

src/lib/ffmpeg/Filter.hxx

@@ -77,63 +77,21 @@ public:
 	}
 };
 
-class FilterContext {
+/**
-	AVFilterContext *context = nullptr;
+ * Create an "abuffer" filter.
+ *
+ * @param the input audio format; may be modified by the
+ * function to ask the caller to do format conversion
+ */
+AVFilterContext &
+MakeAudioBufferSource(AudioFormat &audio_format,
+		      AVFilterGraph &graph_ctx);
 
-public:
+/**
-	FilterContext() = default;
+ * Create an "abuffersink" filter.
-
+ */
-	FilterContext(const AVFilter &filt,
+AVFilterContext &
-		      const char *name, const char *args, void *opaque,
+MakeAudioBufferSink(AVFilterGraph &graph_ctx);
-		      AVFilterGraph &graph_ctx) {
-		int err = avfilter_graph_create_filter(&context, &filt,
-						       name, args, opaque,
-						       &graph_ctx);
-		if (err < 0)
-			throw MakeFfmpegError(err, "avfilter_graph_create_filter() failed");
-	}
-
-	FilterContext(const AVFilter &filt,
-		      const char *name,
-		      AVFilterGraph &graph_ctx)
-		:FilterContext(filt, name, nullptr, nullptr, graph_ctx) {}
-
-	FilterContext(FilterContext &&src) noexcept
-		:context(std::exchange(src.context, nullptr)) {}
-
-	/* note: we don't need a destructor calling avfilter_free()
-	   here because the AVFilterGraph owns and frees all the
-	   AVFilterContext instances */
-	// TODO: do we really need this wrapper class anymore?
-
-	FilterContext &operator=(FilterContext &&src) noexcept {
-		using std::swap;
-		swap(context, src.context);
-		return *this;
-	}
-
-	/**
-	 * Create an "abuffer" filter.
-	 *
-	 * @param the input audio format; may be modified by the
-	 * function to ask the caller to do format conversion
-	 */
-	static FilterContext MakeAudioBufferSource(AudioFormat &audio_format,
-						   AVFilterGraph &graph_ctx);
-
-	/**
-	 * Create an "abuffersink" filter.
-	 */
-	static FilterContext MakeAudioBufferSink(AVFilterGraph &graph_ctx);
-
-	auto &operator*() noexcept {
-		return *context;
-	}
-
-	auto *get() noexcept {
-		return context;
-	}
-};
 
 class FilterGraph {
 	AVFilterGraph *graph = nullptr;