Views Per Hour (VPH) aka view velocity is a great way to determine which videos are taking off to become viral. You can use vidIQ to keep tabs on your videos and your competitors.
VPH is also important to Youtube search rankings because it tells YouTube which videos are trending, surfacing them more frequently all over the site.
Quick Tip! VPH updates over time so even if a video is older you can still see if viewership is heating up! With Pro you can also detect which videos are achieving the highest VPH.