[MPlayer-users] Subliminal image detection
info at vtnd.de
Thu Dec 9 09:17:57 CET 2010
> 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
And if you've found one, be sure to drop a line on this list, I'm sure
such a sample would be welcome.
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