Chromecast lets you "cast" a tab from chrome, but the performance will be subpar. Very subpar. Don't try to watch a video with that or anything. If your macs are all modern enough (sandy bridge or newer) AirPlay display mirroring/extending works pretty well. The latency is noticeable but not the end of the world if you're using it to consume content. You won't want to full screen a 1080p video in VLC though, the framerate will be good but not perfect. There's an app Beamer that can be used for things like that. For most video files it won't need to transcode the whole thing, rather it'll just demux and maybe transcode the audio to AAC (appletv can natively play common video formats).