problems with consistent video duration

[David Vinson]

Hi Lindsay,

Unfortunately it can be a lot of work to get videos to display 
correctly, and it looks like you've gone through a sensible process so 
far.   We experienced something similar, and suspected it could be 
related to the time it takes to load the video files from the hard drive 
and get them displayed in time.  We might not be correct but we managed 
to eliminate these problems (or at least sufficiently reduce them) by a 
combination of a few factors:

1. pre-load the video (e.g. MovieDisplay1.Load in an inline object) well 
before the movie is due to start playing
2. include a fairly high % of breaks between trials if possible, which 
may help resolve the buildup of lag
3. if you are using an older/slower machine it may be useful to have 
video files on a different hard drive than the one being used for 
virtual memory

And 4. a bit more "trial and error" with video formats.  Keep in mind 
that just converting from one video format to another may not be 
sufficient - it may be necessary to re-compress with a different codec.

In troubleshooting these matters it may also be helpful to set up the 
simplest possible miniature version of your experiment (e.g. just one or 
two videos) repeated many times in the simplest possible trial sequence, 
and see if your problem reproduces under those conditions.

OR.... am I missing something here - if one of your videos is 13 sec and 
you only display it for 7 seconds, this would cut it off about halfway 
through.  But surely it's not as simple as this.

good luck, and please report back to the list if you figure it out.
-dv



On 25/02/2012 20:06, Lindsay wrote:
> I am setting up an experiment with videos and am playing around with
> displaying the videos to make sure it will work for our study. The
> videos will play, but they will not play for the whole length every
> time. I am using two practice videos, one 13 seconds and one 6 seconds
> long, and have the program set up to randomly pull them from a list
> and play them after a blank screen. I have tried pre-release, changing
> the run time of the videos, and various video formats, but have not
> had much success. When I increase the number of cycles, some of the
> presentations will run the whole time and some will cut off half-way
> through. The timing of the presentation of stimuli is not necessarily
> important, but we need each video to run for the set length of time
> (about 7 seconds).
>
> We are expanding upon a study that used still images, so we are not as
> familiar with the various video formats, compressions, etc. I would
> appreciate any help!
>
> Lindsay
>

-- 
David Vinson, Ph.D.
Senior Postdoctoral Researcher
Cognitive, Perceptual and Brain Sciences Research Department
University College London
26 Bedford Way, London WC1H 0AP
Tel +44 (0)20 7679 5311  (UCL internal ext. 25311)


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