Long term, the only robust way to solve this is going to involve a remote attestation chain i.e. video that's being signed by the web cam as it's produced, and then transformed/recompressed inside e.g. SGX enclaves or an SEV protected virtual machine that's sending an RA to the other side. Although hard to set up (you need a lot of people to cooperate and CPU vendors have to bring these features back to consumer hardware), it has a lot of advantages over what you might call trick-based approaches:

1. Robust to AI improvements.

2. Blocks all kinds of faking and tampering, not just deepfakes.

3. With a bit of work can securely timestamp the video such that it can become evidence useful for dispute resolution.

4. Also applies to audio.

5. Works in the static/offline scenario where you just get a video file and have to check it.

There are probably other advantages too. The way to do such things has been known about for a long time. The issue is not any missing pieces of tech but simply building a consensus amongst hardware vendors that there's actual market demand for [deep]fake-proof IO.

In reality, deepfakes have been around for some years now but have there been any reports of actual real world attacks using them? Not sure, I didn't hear of any but maybe there's been one or two. Problem is, that's not enough to sustain a market. Attacks have to become pretty common before it's worth throwing anything more than cheap heuristics at it.