[vlc-devel] Why is my subpicture getting displayed for more time than specified?

Robert Forsman bob.forsman at ericsson.com
Wed Apr 25 16:05:22 CEST 2012

On Wed, 25 Apr 2012 01:34:57 -0400
Kaarlo Räihä <kaarlo.raiha at gmail.com> wrote:

> 24. huhtikuuta 2012 21.07 Peter Tap <ptrtap at yahoo.com> kirjoitti:
> Hi Remi,
> Thank you for your help.
> The issue we have is that operators in some of our movie theaters do not
> monitor if someone is video recording the movie off the screen. If we
> get our hands on such a pirated movie, we would like to be able to identify the theater the movie was recorded from.
> The idea was to implement a
> watermarking scheme that is invisible to the human eye but caught by the video camera. My thought was that if we show the hardware id for a very small time, perhaps we could achieve this.
> If we show the text at the same location, pirates can use a video editing software and wipe that region off. We have to find a way to discourage pirates from editing the movie. If we show the id at random location on the screen, frame by frame, it would become very hard for the pirates to edit the movie.

Some of the earlier schemes use patterns of dots that darken or lighten
small parts of the picture for a single frame.  This is less noticable
by humans than text which completely overwrites a bit of the video.

However, there are also single-frame dots that indicate to the
projector when to activate the second reel, and these are detectable by
humans too.

The point is that humans can see things even in a single frame of a
movie, so you'll have to make it unobtrusive enough that they don't

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