frame refactoring, add audio frame and sdl default device input

src/content/sdl_audio_frame_stream2.hpp

@@ -0,0 +1,37 @@
+#pragma once
+
+#include "./frame_stream2.hpp"
+#include "./audio_stream.hpp"
+
+#include <SDL3/SDL.h>
+
+#include <cstdint>
+#include <variant>
+#include <vector>
+#include <thread>
+
+// we dont have to multiplex ourself, because sdl streams and virtual devices already do this, but we do it anyway
+using SDLAudioInputFrameStream2Multiplexer = QueuedFrameStream2Multiplexer<AudioFrame>;
+using SDLAudioInputFrameStream2 = SDLAudioInputFrameStream2Multiplexer::reader_type_t; // just use the default for now
+
+// object components?
+struct SDLAudioInputDevice : protected SDLAudioInputFrameStream2Multiplexer {
+	std::unique_ptr<SDL_AudioStream, decltype(&SDL_DestroyAudioStream)> _stream;
+
+	std::atomic<bool> _thread_should_quit {false};
+	std::thread _thread;
+
+	// construct source and start thread
+	// TODO: optimize so the thread is not always running
+	SDLAudioInputDevice(void);
+
+	// stops the thread and closes the device?
+	~SDLAudioInputDevice(void);
+
+	using SDLAudioInputFrameStream2Multiplexer::aquireReader;
+	using SDLAudioInputFrameStream2Multiplexer::releaseReader;
+};
+
+struct SDLAudioOutputDevice {
+};
+