frame refactoring, add audio frame and sdl default device input

src/content/audio_stream.hpp

@@ -0,0 +1,69 @@
+#pragma once
+
+#include "./frame_stream2.hpp"
+
+#include <solanaceae/util/span.hpp>
+
+#include <cstdint>
+#include <variant>
+#include <vector>
+
+// raw audio
+// channels make samples interleaved,
+// planar channels are not supported
+struct AudioFrame {
+	// sequence number, to detect gaps
+	uint32_t seq {0};
+	// TODO: maybe use ts instead to discard old?
+	// since buffer size is variable, some timestamp would be needed to estimate the lost time
+
+	// samples per second
+	uint32_t sample_rate {48'000};
+
+	size_t channels {0};
+	std::variant<
+		std::vector<int16_t>, // S16, platform endianess
+		Span<int16_t>, // non owning variant, for direct consumption
+
+		std::vector<float>, // f32
+		Span<float> // non owning variant, for direct consumption
+	> buffer;
+
+	// helpers
+
+	bool isS16(void) const {
+		return
+			std::holds_alternative<std::vector<int16_t>>(buffer) ||
+			std::holds_alternative<Span<int16_t>>(buffer)
+		;
+	}
+	bool isF32(void) const {
+		return
+			std::holds_alternative<std::vector<float>>(buffer) ||
+			std::holds_alternative<Span<float>>(buffer)
+		;
+	}
+	template<typename T>
+	Span<T> getSpan(void) const {
+		static_assert(std::is_same_v<int16_t, T> || std::is_same_v<float, T>);
+		if constexpr (std::is_same_v<int16_t, T>) {
+			assert(isS16());
+			if (std::holds_alternative<std::vector<int16_t>>(buffer)) {
+				return Span<int16_t>{std::get<std::vector<int16_t>>(buffer)};
+			} else {
+				return std::get<Span<int16_t>>(buffer);
+			}
+		} else if constexpr (std::is_same_v<float, T>) {
+			assert(isF32());
+			if (std::holds_alternative<std::vector<float>>(buffer)) {
+				return Span<float>{std::get<std::vector<float>>(buffer)};
+			} else {
+				return std::get<Span<float>>(buffer);
+			}
+		}
+		return {};
+	}
+};
+
+using AudioFrameStream2I = FrameStream2I<AudioFrame>;
+