请解释下这段代码namespace cros { // This class interfaces with the Google3 auto-framing library: // http://google3/chromeos/camera/lib/auto_framing/auto_framing_cros.h class AutoFramingClient : public AutoFramingCrOS::Client { public: struct Options { Size input_size; double frame_rate = 0.0; uint32_t target_aspect_ratio_x = 0; uint32_t target_aspect_ratio_y = 0; }; // Set up the pipeline. bool SetUp(const Options& options); // Process one frame. |buffer| is only used during this function call. bool ProcessFrame(int64_t timestamp, buffer_handle_t buffer); // Return the stored ROI if a new detection is available, or nullopt if not. // After this call the stored ROI is cleared, waiting for another new // detection to fill it. std::optional<Rect<uint32_t>> TakeNewRegionOfInterest(); // Gets the crop window calculated by the full auto-framing pipeline. Rect<uint32_t> GetCropWindow(); // Tear down the pipeline and clear states. void TearDown(); // Implementations of AutoFramingCrOS::Client. void OnFrameProcessed(int64_t timestamp) override; void OnNewRegionOfInterest( int64_t timestamp, int x_min, int y_min, int x_max, int y_max) override; void OnNewCropWindow( int64_t timestamp, int x_min, int y_min, int x_max, int y_max) override; void OnNewAnnotatedFrame(int64_t timestamp, const uint8_t* data, int stride) override; private: base::Lock lock_; std::unique_ptr<AutoFramingCrOS> auto_framing_ GUARDED_BY(lock_); std::unique_ptr<CameraBufferPool> buffer_pool_ GUARDED_BY(lock_); std::map<int64_t, CameraBufferPool::Buffer> inflight_buffers_ GUARDED_BY(lock_); std::optional<Rect<uint32_t>> region_of_interest_ GUARDED_BY(lock_); Rect<uint32_t> crop_window_ GUARDED_BY(lock_); }; } // namespace

这段代码是定义了一个名为AutoFramingClient的类，该类继承自AutoFramingCrOS::Client。AutoFramingClient是一个与Google3自动裁剪库进行交互的类，用于视频流的自动裁剪。具体地，AutoFramingClient实现了SetUp、ProcessFrame、TakeNewRegionOfInterest、GetCropWindow和TearDown这几个函数，分别用于设置自动裁剪的参数、处理视频流的一帧、获取新的感兴趣区域（Region of Interest，ROI）、获取自动裁剪的窗口以及清除状态。此外，AutoFramingClient还实现了AutoFramingCrOS::Client中的几个回调函数，用于处理自动裁剪库返回的信息。在AutoFramingClient的实现中，使用了base::Lock进行线程同步，并使用了std::map和std::unique_ptr等C++标准库提供的容器和智能指针来管理内存。