Install K-lite codec see if that helps, also try IE.
I've used IE, Chrome and also Opera. The stuttering happened with each browser.
Are you using any mechanical drives? One of them could be going bad causing the stuttering.
Nope, there's a SSD in my HTPC. But I've pretty much figured out that it's the motherboard / processor combo that's in my HTPC. I posted a thread in the HTPC section and was recommended a better / faster / newer motherboard & processor for the HTPC that can handle the video playback smoothly. Also, I've been temporarily using my i5 laptop on WiFi connected with a HDMI cable and everything plays pretty smooth. So another bit of proof that it's the older HTPC components that were causing the issues .