The zero-copy option is only applicable to Mac clients. The zero-copy option tells your client to keep all video data in the GPU memory rather than moving it to system memory. When zero-copy is on, the data stays in video RAM and is rendered directly from video memory to the screen. If it's not zero-copy, the video data is decoded into video memory, copied to system memory, then copied back into video memory, and then rendered. Zero-copy is currently default off (value of the setting is 0). If you want to lower your latency on a Mac, please set the value to 1.