Ladybird: Move the AudioThread class into its own file

This implementation detail of audio support in ladybird is a QObject
that needs moc'd by the moc tools. Putting it in its own file follows
the pattern we have for all the other QObjects in Ladybird.

Ladybird/AudioThread.h

@@ -0,0 +1,103 @@
+/*
+ * Copyright (c) 2023, Tim Flynn <trflynn89@serenityos.org>
+ * Copyright (c) 2023, Andrew Kaster <akaster@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Endian.h>
+#include <AK/MemoryStream.h>
+#include <AK/Optional.h>
+#include <AK/Types.h>
+#include <LibAudio/Loader.h>
+#include <LibAudio/Sample.h>
+#include <LibCore/SharedCircularQueue.h>
+#include <QAudioFormat>
+#include <QAudioSink>
+#include <QByteArray>
+#include <QMediaDevices>
+#include <QThread>
+
+namespace Ladybird {
+
+static constexpr u32 UPDATE_RATE_MS = 10;
+
+struct AudioTask {
+    enum class Type {
+        Stop,
+        Play,
+        Pause,
+        Seek,
+        Volume,
+        RecreateAudioDevice,
+    };
+
+    Type type;
+    Optional<double> data {};
+};
+
+using AudioTaskQueue = Core::SharedSingleProducerCircularQueue<AudioTask>;
+
+class AudioThread final : public QThread { // We have to use QThread, otherwise internal Qt media QTimer objects do not work.
+    Q_OBJECT
+
+public:
+    static ErrorOr<NonnullOwnPtr<AudioThread>> create(NonnullRefPtr<Audio::Loader> loader);
+
+    ErrorOr<void> stop();
+
+    Duration duration() const { return m_duration; }
+
+    ErrorOr<void> queue_task(AudioTask task);
+
+Q_SIGNALS:
+    void playback_position_updated(Duration);
+
+private:
+    AudioThread(NonnullRefPtr<Audio::Loader> loader, AudioTaskQueue task_queue);
+
+    enum class Paused {
+        Yes,
+        No,
+    };
+
+    void run() override;
+
+    ErrorOr<Paused> play_next_samples(QAudioSink& audio_output, QIODevice& io_device);
+
+    void enqueue_samples(QAudioSink const& audio_output, QIODevice& io_device, FixedArray<Audio::Sample> samples);
+
+    template<typename T>
+    void write_sample(FixedMemoryStream& stream, float sample)
+    {
+        // The values that need to be written to the stream vary depending on the output channel format, and isn't
+        // particularly well documented. The value derivations performed below were adapted from a Qt example:
+        // https://code.qt.io/cgit/qt/qtmultimedia.git/tree/examples/multimedia/audiooutput/audiooutput.cpp?h=6.4.2#n46
+        LittleEndian<T> pcm;
+
+        if constexpr (IsSame<T, u8>)
+            pcm = static_cast<u8>((sample + 1.0f) / 2 * NumericLimits<u8>::max());
+        else if constexpr (IsSame<T, i16>)
+            pcm = static_cast<i16>(sample * NumericLimits<i16>::max());
+        else if constexpr (IsSame<T, i32>)
+            pcm = static_cast<i32>(sample * NumericLimits<i32>::max());
+        else if constexpr (IsSame<T, float>)
+            pcm = sample;
+        else
+            static_assert(DependentFalse<T>);
+
+        MUST(stream.write_value(pcm));
+    }
+
+    NonnullRefPtr<Audio::Loader> m_loader;
+    AudioTaskQueue m_task_queue;
+
+    QByteArray m_sample_buffer;
+
+    Duration m_duration;
+    Duration m_position;
+};
+
+}