A word about M2TS - it is a container format for high definition video files on Blu-ray and AVCHD. A lot of HD camcorders, like Sony HDR-CX100, JVC GZ-HD40, Panasonic HDC-HS300 make videos in M2TS format. But not every player can handle is format once you transfer files from camcorder to computer.
Elmedia Player is easily the best M2TS Mac player including macOS Sierra. It is rather easy to play M2TS on Mac, just follow the steps below:
It can be quite challenging to play M2TS on Mac. Of course you can try converting M2TS to other file formats, playing M2TS in QuickTime on 10.11 Mountain Lion or newer or using VLC player, which is not the perfect choice because of various issues with this format: freezing up, video and sound not in sync, no video or audio, etc.
This M2TS player is so good that it doesn't limit you to M2TS files only. You can watch many other videos in various formats. And in case you want to download M2TS files from the web you can do this with Elmedia Player PRO.
Give a chance to Elmedia Player as your M2TS player Mac app. Elmedia is free and doesn't require additional codec/plugins/components, or converting file formats.