You almost certainly won't be able to do what you want either (and both computers being on the same workgroup over the internet is a load of rubbish)
To watch a video from a PC over the internet the PC with the video on it would need to have a higher upstream internet speed than the bitrate of the video, so if the video was at 1000Kb/s the computer with it on would need to be able to send the data at about 1200Kb/s..... most people only have about 500Kb/s upload speed.
If by chance the computer hosting the video has got enough bandwidth to make it feasible then setting up a VPN would be your best option, then you can treat the remote machine exactly the same as you would a machine on your local network.