Add a GenericHwAccelRenderer for unknown hwaccels

This will get us limited hardware acceleration even for hwaccels
that we don't know about yet.

app/streaming/video/ffmpeg-renderers/genhwaccel.h

@@ -0,0 +1,21 @@
+#pragma once
+
+#include "renderer.h"
+
+class GenericHwAccelRenderer : public IFFmpegRenderer
+{
+public:
+    GenericHwAccelRenderer(AVHWDeviceType hwDeviceType);
+    virtual ~GenericHwAccelRenderer() override;
+    virtual bool initialize(PDECODER_PARAMETERS) override;
+    virtual bool prepareDecoderContext(AVCodecContext* context, AVDictionary** options) override;
+    virtual void renderFrame(AVFrame* frame) override;
+    virtual bool needsTestFrame() override;
+    virtual bool isDirectRenderingSupported() override;
+    virtual int getDecoderCapabilities() override;
+
+private:
+    AVHWDeviceType m_HwDeviceType;
+    AVBufferRef* m_HwContext;
+};
+