LibVideo: Abstract media container format demuxing

This creates an abstract Demuxer class to allow multiple container
container formats to be easily used by video playback systems.

Userland/Libraries/LibVideo/Sample.h

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+/*
+ * Copyright (c) 2022, Gregory Bertilson <zaggy1024@gmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/ByteBuffer.h>
+#include <AK/Time.h>
+#include <LibVideo/Color/CodingIndependentCodePoints.h>
+
+namespace Video {
+
+class Sample {
+public:
+    virtual ~Sample() = default;
+
+    virtual bool is_video_sample() const { return false; }
+};
+
+class VideoSample : public Sample {
+public:
+    VideoSample(ByteBuffer const& data, CodingIndependentCodePoints container_cicp, Time timestamp)
+        : m_data(data)
+        , m_container_cicp(container_cicp)
+        , m_timestamp(timestamp)
+    {
+    }
+
+    bool is_video_sample() const override { return true; }
+    ByteBuffer const& data() const { return m_data; }
+    CodingIndependentCodePoints container_cicp() const { return m_container_cicp; }
+    Time timestamp() const { return m_timestamp; }
+
+private:
+    ByteBuffer m_data;
+    CodingIndependentCodePoints m_container_cicp;
+    Time m_timestamp;
+};
+
+// FIXME: Add samples for audio, subtitles, etc.
+
+}