I can't confirm but I'm pretty sure they may have switched video tech partners. I did notice a few changes around a month ago, but It could potentially be an updated platform from the same supplier.
What it seems to do is optimise on the fly for internet speed, so it flickers between renditions of the same videos. I have a crap usb modem and I've had HD quality, then flicker to average, and then poor, and then again to super poor. You can hear the audio quality change as well. I don't think many people would have the same issues but it's definitely different from before when it would assign a specific quality and then that's what you had, it would just take more time to buffer etc.