> this feature is algorithmically impossible
> You're just looking at one specific video, not the general problem.
> is not generally possible.
As a fellow multimedia dev, man, who cares? Sometimes we forget that software ought to be useful, not hypothetical ideals of truth. Just implement the feature for those codecs that support it and which probably are in the 98% percentile of what users actually use, regardless of the damned "general case".
Or accept and announce shamelessly that you don't have either the knowledge or the development resources to tackle such a complex feature. But excuses about not being possible for absolutely every possible codec in a completely generic way is just denying that the world is just a chaotic and dirty place where things are not ideal nor perfect. Just give your users a real-world solution (or rejection).
I don't know how they get away with that though. In the coding work that I do, I'm constantly dealing with rules that have exceptions on top of exceptions. I just need to special-case some things, because the alternative is not delivering what the business needs.