Presenting slide-object while video is playing

[David McFarlane]

Francesco,

Since you asked for suggestions, I took a little 
trip down memory lane, to the days before we 
limited our methodology to what could be done 
with digital computers.  Back in the early 1980s 
I did visual psychophysics, and back then if we 
needed to superimpose stimuli we would just use a 
half-silvered mirror set at 45° in front of the 
subject.  So here's how you could do this the 
old-school way:  Present your movie on one 
display screen, and your overlay on a second 
display screen (EP2 can do this now).  Put a 
half-silvered mirror in front of the subject, 
angled 45° relative to the subject.  Put one 
display (e.g., the movie) straight beyond the 
mirror, and the second display off at 90° to the mirror.
Voilà!  Now the subject looks through the mirror 
and sees the two displays combined.

You might also achieve much the same effect with 
a pair of video projectors aimed at the same 
screen.  Of course, these methods make both 
displays translucent, so if you want, say, the 
red square to completely occlude the underlying 
video then this will not work.  I cannot think of 
any way around that, perhaps someone else can do better.

-- David McFarlane


At 5/15/2012 10:24 AM Tuesday, David McFarlane wrote:
>Francesco,
>
>Both MATLAB and Presentation have better visual 
>stimulus capabilities than E-Prime (though I 
>don't know anything about how they do 
>video).  Even so, I would not be surprised if 
>they failed to do what you ask here.  Due to the 
>very nature of video presentations, what you ask 
>requires real-time on-the-fly video mixing 
>capabilities, which is a very tall order.  I 
>know that intuitively, overlapping a couple of 
>visual stimuli seems trivial, but if you think 
>through the mechanics of how moving images are 
>made by rewriting the screen with each frame, 
>you will see that overlapping stimuli with video is not at all trivial.
>
>Good luck,
>-- David McFarlane
>
>
>At 5/15/2012 04:33 AM Tuesday, francesco.biondi at ymail.com wrote:
>>Hi David,
>>
>>the target (eg, a red square) I need to show to 
>>participants overlays the video,
>>then I cannot use a Slide Objects composed by multiple objects (video+text).
>>
>>I ve seen you mentioned Matlab; I thought to consider it, but I have no
>>updates from that side.
>>
>>Indeed, about video-editing I am trying to run 
>>this way, but I think I would have problems
>>with timing, because I should consider both the 
>>video's frame-rate and the monitor refresh-rate;
>>I guess this may be problematic for the reliability of recorded times.
>>
>>Suggestions?
>>
>>2012/5/14 David McFarlane <<mailto:mcfarla9 at msu.edu>mcfarla9 at msu.edu>
>>Does any part of your superimposed text overlap 
>>with the video?  If so, then you will run into 
>>the problem discussed at 
>><http://groups.google.com/group/e-prime/browse_thread/thread/2bcf7ebef4211832>http://groups.google.com/group/e-prime/browse_thread/thread/2bcf7ebef4211832 
>>.
>>
>>-----
>>David McFarlane
>>E-Prime training online: 
>><http://psychology.msu.edu/Workshops_Courses/eprime.aspx>http://psychology.msu.edu/Workshops_Courses/eprime.aspx
>>Twitter:  @EPrimeMaster 
>>(<http://twitter.com/EPrimeMaster>twitter.com/EPrimeMaster)
>>
>>
>>
>>At 5/14/2012 08:14 AM Monday, francesco biondi wrote:
>>I ve just realised I made a mistake..
>>
>>when I write slide-objects
>>I mean text-objects
>>
>>Sorry
>>
>>waiting for reply!
>>
>>Il giorno lunedì 14 maggio 2012 11:53:50 UTC+2, francesco biondi ha scritto:
>>Hi all!
>>I ve posted a topic on PSTforum but..no reply yet..
>>then, I will turn my problem over to you..
>>
>>
>>I need to show a video to participants using a MovieDisplay-object.
>>While the video is playing, I need to show, superimposed to the video,
>>some slide-objects covering not the whole display, but only a small
>>part of it. After participant's response to the object, the object
>>will disappear, but the video will continue without any interruption.
>>
>>I dont know how I can show slide-objects together with the video
>>without interrupting it (letting it play without crashes).
>>
>>Bye!
>>
>>and thanks in advance
>>
>>--
>>Francesco Biondi

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