VideoToolBox decoder/encoder for MacOS & iOS (#19)

* VideoDecoderFactory wrapper

* wip

* fix compilation

* add notes

* upgrade webrtc version

webrtc-sys/include/livekit/objc_video_factory.h

@@ -0,0 +1,15 @@
+#ifndef OBJC_VIDEO_FACTORY_H
+#define OBJC_VIDEO_FACTORY_H
+
+#include <memory>
+#include "api/video_codecs/video_decoder_factory.h"
+#include "api/video_codecs/video_encoder_factory.h"
+
+namespace livekit {
+
+std::unique_ptr<webrtc::VideoEncoderFactory> CreateObjCVideoEncoderFactory();
+std::unique_ptr<webrtc::VideoDecoderFactory> CreateObjCVideoDecoderFactory();
+
+}  // namespace livekit
+
+#endif // OBJC_VIDEO_FACTORY_H