<html><body><div style="color:#000; background-color:#fff; font-family:times new roman, new york, times, serif;font-size:12pt"><div><span>The location is generated randomly all over the screen. Each frame shows the watermark on a different location. It will be very hard for the attacker to edit frame by frame.</span></div><div><br><span></span></div><div><span>The random number generator is the one that VLC provides (vlc_lrand48). I can see that the numbers are getting displayed at different location.</span></div><div><br><span></span></div><div><span>What is confusing is why do I see the numbers. The timeout value is for just one frame.</span></div><div><br><span></span></div><div><span>Regards,</span></div><div><span>Peter<br></span></div><div><br></div> <div style="font-family: times new roman, new york, times, serif; font-size: 12pt;"> <div style="font-family: times new roman, new york, times, serif; font-size: 12pt;"> <div dir="ltr"> <font
face="Arial" size="2"> <hr size="1"> <b><span style="font-weight:bold;">From:</span></b> Frederic YHUEL <fyhuel@viotech.net><br> <b><span style="font-weight: bold;">To:</span></b> Mailing list for VLC media player developers <vlc-devel@videolan.org> <br> <b><span style="font-weight: bold;">Sent:</span></b> Tuesday, April 10, 2012 1:43 AM<br> <b><span style="font-weight: bold;">Subject:</span></b> Re: [vlc-devel] Ephemeral timeout not working on subpictures<br> </font> </div> <br>
On Tue, Apr 10, 2012 at 12:57 AM, Peter Tap <<a ymailto="mailto:ptrtap@yahoo.com" href="mailto:ptrtap@yahoo.com">ptrtap@yahoo.com</a>> wrote:<br>> Hello,<br>><br>> I am trying to implement a watermarking scheme that is not visible to human<br>> eye. The idea is to display a small subpicture at random location for each<br>> frame. There are 24 frames per second. Human eye should not catch the<br>> subpicture if it is displayed only for 1/24th part of a second.<br>><br>> My computed timeout for each subpicture is CEIL((1 * 1000 * 1000), 24)<br>> nanoseconds.<br>><br>> In my video filter, here is the relevant code for subpicture settings:<br>><br>> p_spu->i_start = date;<br>> p_spu->i_stop = date + p_sys->i_timeout; // timeout from above<br>> calculations<br>> p_spu->b_ephemer = true; // the subpicture is ephemeral<br>>
p_spu->b_fade = false; // no fading. Just disappear<br>><br>> However, when I run vlc, I still see the subpicture appearing momentarily.<br>><br>> Thinking that my calculation is wrong, I modified the stop time to current<br>> time + 1 nanosecond.<br>><br>> p_spu->i_stop = date + 1;<br>><br>> However, that doesn't seem to make any difference. I still see the image<br>> momentarily on the screen.<br>><br><br>Is it possible that you use a really crappy prng? Did you check that<br>the location actually change each time?<br><br>And btw, such a watermarking scheme doesn't seem really robust... I'm<br>not a specialist, but an attacker could easily remove the watermark,<br>no?<br><br>-- <br>Frédéric<br>_______________________________________________<br>vlc-devel mailing list<br>To unsubscribe or modify your subscription
options:<br>http://mailman.videolan.org/listinfo/vlc-devel<br><br><br> </div> </div> </div></body></html>