Comment by javajosh
4 years ago
This brings up an interesting question: what is the upper-bound of hidden data density using video steganography? E.g. how much extra data can you add before noticeable degradation? It's interesting because it requires both a detailed understanding of video encoding and also understanding of human perception of video.
I've seen drone metal videos where the video and audio could both be 90% steganography and I wouldn't know the difference.
I'd expect you could store more data steganographically than the raw video data.
You can probably do things like add frames that can't be decoded and so are skipped by a decoder; that effectively allows arbitrary added hidden data. That's maybe cheating.
If you stipulate that you can't already have a copy of the unaltered file, and the data has to be extractable from a pixel copy of the rendered frames ... that becomes more interesting, I think.
Youtube doesn't give you the raw video back, it does transcoding to their given standard bitrates/resolution sets.
You'll notice this if someone has just uploaded a video to Youtube and the only version available for playback is some 360p/480p version for a few hours until Youtube gets around to processing higher bitrates.
So whatever you're encoding has to survive that transcode process.
A pretty massive amount I imagine. I attended a lecture on single image steganography and they were able to store almost 25% of the image's size and it was barely visible. Even 50% didn't look too bad.
Extending that into video files and it would likely be pretty massive, although you'd have some interesting time with youtube's compression algorithms