[MPlayer-users] Subliminal image detection

[Oliver Seitz]

> so it would be useful to know which subliminal images you were looking to detect
> and if so, samples of these would be required to build detection for them.

If subliminal advertising did work, and the most famous studies on the 
subject are now known to be fraud, it would really be interesting.

But it's not that hard at all. You wouldn't need reference pictures. A 
"subliminal" picture would be a perfectly normal frame, displaying for 
about 17 to 67 milliseconds, depending on the frame rate of the 
surrounding film. Frame rates of more than 30fps are rare, so the time 
is usually longer than 33 milliseconds. That's almost certainly 
supraliminal, so it's questionable if subliminal pictures can at all be 
embedded in internet video streams.

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.

Try the "framestep=i" filter, and make a script to find adjacent 
keyframes. This will at least show if there *could* be subliminal frames 
inside a video.

Then play the part in question again with -speed 0.05 to easily see the 
picture.

And if you've found one, be sure to drop a line on this list, I'm sure 
such a sample would be welcome.

Greets,
Kiste