LibVideo: Make VP9::Decoder a subclass of a new abstract VideoDecoder

This will allow other decoders to be used in place of VP9::Decoder when
new video decoders are implemented, such as AV1.

Userland/Libraries/LibVideo/VideoDecoder.h

@@ -0,0 +1,26 @@
+/*
+ * Copyright (c) 2022, Gregory Bertilson <zaggy1024@gmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/ByteBuffer.h>
+#include <AK/NonnullOwnPtr.h>
+
+#include "DecoderError.h"
+#include "VideoFrame.h"
+
+namespace Video {
+
+class VideoDecoder {
+public:
+    virtual ~VideoDecoder() {};
+
+    virtual DecoderErrorOr<void> receive_sample(Span<u8 const> sample) = 0;
+    DecoderErrorOr<void> receive_sample(ByteBuffer const& sample) { return receive_sample(sample.span()); }
+    virtual DecoderErrorOr<NonnullOwnPtr<VideoFrame>> get_decoded_frame() = 0;
+};
+
+}