[nicce]

For editing it does not matter if you just remove or move frames. Video is just a series frames and each of them are signed, each frame can be validated if the content is unmodified. If the same root key is used for another stream, then frames can be combined easily.

I don't know audio well enough how it happens there. But potentially it can be signed in chunks as well.

Of course, one needs to consider risks if editing can make content appear different than originally intended, when the video as "whole" is not signed. But for that, different entity can be used again.

[rtkwe]

You do get into issues because video files aren't just raw frames and haven't been for ages. Plus any changes on top of the video wouldn't just pass the frames through beyond the fact that current video encoding would reencode the embedded video when the larger video it was embedded in was exported. You'd have to add support for seamless passthrough of the original frames so the signatures could be validated plus some additional layers if you wanted to enable having graphics on top of the footage.

It would require completely changing how software currently handles video editing in short.

[nicce]

Let's say that camera records in 60fps. Maybe all the data on all the channels can be recorded in chunks of 1/60s and signed separated. Then camera combines it as whole playable video, but then there is a separate metadata for each time/byte offset which have been signed.

At the beginning, camera manufacturers might need to provide their own editors, to make editing possible. How much we can trust the camera holders, if the editor software even allows using the key from the camera for better editing in certain limits?

[rtkwe]

Intraframe compression where each frame is individually compressed is barely used any more outside of movies and other professional nonsteamed production because it barely compresses the resulting video. Most streaming and consumer video cameras use interframe compression where you get a full frame every few frames and the rest are moving pieces of that around. This video by Captain Disillusion [0] goes over it much better than I can and any time the video is edited it goes through that process again of creating I-frames P-frames and whatever new homunculus frames are invented to further compress video while maintaining quality.

If you just cut away to the original clip and didn't have any modifications like motion graphics over the top of it you could in theory pass through the original video with the same compression and signing without too much drama but any modifications over that or presenting it as picture in picture would be a big difference as now you need to have both the original frames with the added graphics on top.

[0] https://youtu.be/flBfxNTUIns?t=139

[aqme28]

> video files aren't just raw frames and haven't been for ages.

Does that really matter? You could sign keyframes, and then also sign the differences frame by frame til you get to the next keyframe.

[rtkwe]

You could but then that only really works for rehosting the exact same video. Most places would at least embed it in another video for commentary which would have a reencoding step that would wipe out the original video. See my other comments for more detail but it would require changing how we handle videos to preserve the signing info.

[aqme28]

That's a problem with embedding then, not with compression, right? Would embedding a raw video with commentary not also have the same problem?

[mcpackieh]

Follow the discussion chain back up: jacobsimon's posed the question: "How would that work with video editing?"

The answer is that it doesn't. Some might try to make it work by using proprietary video editing software that signs a ledger of what edit operations were performed, or something like that, but that doesn't work. The signing keys will eventually be extracted from the video editor or the camera, or the video editor or camera will be hacked to sign something it shouldn't. You might say that this at least stops low-skilled attackers, but the misinformation that is most dangerous to humanity, that created by governments to start wars, won't be impeded by any of these schemes. The whole cryptographic signature proposal is worse than useless.

[rtkwe]

You've nailed it this whole thread is about actually using the footage in anything other than it's raw original format. As soon as you start embedding it in other footage to say present and comment on it you run into all sorts of issues dealing with maintaining the signatures.