So this uses ethereum to verify that a video was taken at a certain time. Altering the video is impossible, because the altered video will necessarily be create

So this uses ethereum to verify that a video was taken at a certain time. Altering the video is impossible, because the altered video will necessarily be created much later than the original. If you can plan to fake something ahead of time (say, plan to frame someone to rob a bank in a week), then you can still use deepfakes. In principle, if you could create fake video in realtime you could upload it as real, thereby altering realtime at whim. But creating a story after-the-fact would always be impossible (51% notwithstanding).