[MPlayer-users] Subliminal image detection

[Reimar Döffinger]

On Thu, Dec 09, 2010 at 09:17:57AM +0100, Oliver Seitz wrote:
> Finding such pictures would be quite easy: The change in picture
> content, both when the "subliminal" picture is drawn and removed,
> has to be quite big. So for usual internet videos, you can find
> those pictures by just looking for two I-frames in direct
> succession.

A good encoder, at least for H.264, should not need more than
one I-frame (note: not IDR, if it used that it would have to use
two indeed).
For other standards this is probably more difficult (or even impossible)
so for those two consecutive I-frames may indeed be a strong indication.
However your analysis does not take into account variable-frame-rate formats,
which might change things a bit, and of course if you don't care about
coding efficiency those frames can be P-codec as well.
A scene change detection algorithm would be more precise, though much
more effort etc.