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

Tim Ouellette Tim at video-dynamics.com
Wed Apr 25 18:38:43 CEST 2012

I'm going to use a small amount of speculation about movie theatre's modern projection schemes based on what I know after working with some of the Sony folks that are retro fitting current theatres with digital projection systems utilizing HD based video distribution.

You could imbed a watermark that would be invisible to the human eye and would be recordable by a CDD some percentage of the time.  I believe modern films are shown at a rate of 24fps with each frame having 3 shutters thus presenting 72 shot per second (assumption is triple shuttering).  If you were to water mark one of 72 frames every second it would not be noticeable to the human eye however if using a CCD to record at the typical 30fps you would pick up approximately one of every 30 water marks in your visual recording, thus giving you a stamp about twice a minute.  Just something to put a little bit of thought into.


-----Original Message-----
From: vlc-devel-bounces at videolan.org [mailto:vlc-devel-bounces at videolan.org] On Behalf Of Robert Forsman
Sent: Wednesday, April 25, 2012 10:16 AM
To: Mailing list for VLC media player developers
Subject: Re: [vlc-devel] Why is my subpicture getting displayed for more time than specified?

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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