I think chain of custody will be more important than eyewitness testimony in the future. In the case of CCTV or body cam footage, it will be a combination of the footage being digitally signed by the recording device, and being able to prove the footage could not have been tampered with along the way.
So, a record of where and when the footage was recorded, when it was transferred from the device, where it was held after this, and that the storage location was also secure.