try tpt.setfpscap(something smaller than your current fps), and if you don't want to type that every time, put it in a file called autorun.lua next to the tpt exe. This will make tpt use a little less cpu and then you can watch videos without lag (probably). It will still always use 100% cpu when in an interface like the online browser, unless you use the latest beta (tpt++) or my mod (fps limiting there is a little glitchy), where it should use almost 0% cpu.
You could also try using task manager and giving tpt less priority, so that it's less important than other programs and only uses whatever cpu is left after your video loads/plays.