请问2句英文翻译，实在拿不准，多谢

determining which pixels in the current video frame changed from the previous video frame;
确定当前视频帧中的、与前一视频帧发生了变化的像素点

which blocks have changed from frame to frame？
哪些块是在帧间发生了变化的

供参考：

determining which pixels in the current video frame changed from the previous video frame;
确定当前视频帧中哪些像素较前一视频帧发生了变化
which blocks have changed from frame to frame？
哪些块在帧间发生了变化