# Show only part of a video stimulus in psychopy

**URL:** <https://discourse.psychopy.org/t/show-only-part-of-a-video-stimulus-in-psychopy/940>\
**Category:** Coding\
**Created:** [August 23, 2016, 1:58pm UTC](https://discourse.psychopy.org/t/show-only-part-of-a-video-stimulus-in-psychopy/940 "2016-08-23T13:58:17Z")\
**Posts on this page:** 7\
**Page:** 1

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**Author:** ![Horea\_Christian](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.psychopy.org/horea_christian/32/203_2.png) [@Horea\_Christian](https://discourse.psychopy.org/u/Horea_Christian)\
**Post date:** [August 23, 2016, 1:58pm UTC](https://discourse.psychopy.org/t/show-only-part-of-a-video-stimulus-in-psychopy/940/1 "2016-08-23T13:58:17Z")

</div>

Is it possible to have Psychopy’s [`MovieStim`](http://www.psychopy.org/api/visual/moviestim.html#psychopy.visual.MovieStim) play only a certain _spatial_ percentage of a movie file?

I would like to be able to show 0-25% of the x-size of a stimulus, then 25-41% etc. It is not feasible for me to manually crop the videos, because I need to control the crop coordinates at runtime.

I am currently using [this code](https://github.com/TheChymera/behaviopy/blob/master/behaviopy/event_tracking.py), and I was hoping to get the effect I want with the `MovieStim.size` attribute somehow, but that invariably controls the size of the entire movie.

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**Author:** ![jon](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.psychopy.org/jon/32/22_2.png) [@jon](https://discourse.psychopy.org/u/jon)\
**Post date:** [August 23, 2016, 2:06pm UTC](https://discourse.psychopy.org/t/show-only-part-of-a-video-stimulus-in-psychopy/940/2 "2016-08-23T14:06:37Z")

</div>

No, this isn’t a property of MovieStim, but it would be possible by using an aperture of varying size I think. Worst case scenario is that you could cover your movie with squares that are the same color as the background 😉

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**Author:** ![Horea\_Christian](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.psychopy.org/horea_christian/32/203_2.png) [@Horea\_Christian](https://discourse.psychopy.org/u/Horea_Christian)\
**Post date:** [August 23, 2016, 2:25pm UTC](https://discourse.psychopy.org/t/show-only-part-of-a-video-stimulus-in-psychopy/940/3 "2016-08-23T14:25:27Z")

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Could you show me an example of how to use the `Apperture` object?

I tried a few things, including dropping this

```auto
visual.Aperture(win, size=0.2, pos=(0, 0), ori=0, nVert=120, shape='square', inverted=False, units="norm", name=None, autoLog=None)

```

at various points in my code, but ist seems to do nothing.  
Do I need to somehow pass it to the MovieStim object?

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**Author:** ![jon](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.psychopy.org/jon/32/22_2.png) [@jon](https://discourse.psychopy.org/u/jon)\
**Post date:** [August 23, 2016, 2:30pm UTC](https://discourse.psychopy.org/t/show-only-part-of-a-video-stimulus-in-psychopy/940/4 "2016-08-23T14:30:07Z")

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There’s an example in the demos\>stimuli menu.

No, you don’t pass it to anything. When enabled (on by default) it is applied to any other drawing being performed

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**Author:** ![Horea\_Christian](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.psychopy.org/horea_christian/32/203_2.png) [@Horea\_Christian](https://discourse.psychopy.org/u/Horea_Christian)\
**Post date:** [August 23, 2016, 2:41pm UTC](https://discourse.psychopy.org/t/show-only-part-of-a-video-stimulus-in-psychopy/940/5 "2016-08-23T14:41:18Z")

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Strange that it hasn’t worked yet, then. But I hope the usage examlple will clear stuff up.  
I can’t however, find the demo you mentioned (having installed psychopy-1.84.0):

```
PsychoPy2 Demos/
├── BART
│ ├── balloons.xlsx
│ ├── bang.wav
│ ├── bart.psyexp
│ ├── blueBalloon.png
│ ├── greenBalloon.png
│ ├── README.txt
│ ├── redBalloon.png
│ └── trialTypes.xlsx
├── branchedExp
│ ├── branching.psyexp
│ ├── README.txt
│ └── trialTypes.xlsx
├── __init__.py
├── __init__.pyc
├── __init__.pyo
├── iohub
│ ├── stroop_eyetracking
│ │ ├── LC_eyegaze_std.yaml
│ │ ├── README.txt
│ │ ├── SMI_iview_std.yaml
│ │ ├── SRR_eyelink_std.yaml
│ │ ├── stroop.psyexp
│ │ ├── tobii_std.yaml
│ │ └── trialTypes.xlsx
│ └── stroop_keyboard
│ ├── iohub_config.yaml
│ ├── README.txt
│ ├── stroop.psyexp
│ └── trialTypes.xlsx
├── mental_rotation
│ ├── F.png
│ ├── FR.png
│ ├── MentalRot.csv
│ ├── MentalRot.psyexp
│ └── README.txt
├── navon
│ ├── bigHsmallH.png
│ ├── bigHsmallS.png
│ ├── bigSsmallH.png
│ ├── bigSsmallS.png
│ ├── mask.png
│ ├── NavonTask.psyexp
│ ├── README.txt
│ └── trialTypes.xlsx
├── practical IAT
│ ├── All.csv
│ ├── All_rev.csv
│ ├── Creat_Prac.csv
│ ├── Creat_Prac_rev.csv
│ ├── Good_Bad.csv
│ └── IAT.psyexp
├── psychophysicsStaircase
│ ├── psychophysicsStaircase.psyexp
│ └── README.txt
├── psychophysicsStairsInterleaved
│ ├── interleaved_SF_contrast.psyexp
│ ├── README.txt
│ └── stairDefinitions.xlsx
├── ratingScales
│ └── ratingScaleBuilder.psyexp
├── README.txt
├── sternberg
│ ├── mainTrials.xlsx
│ ├── pracTrials.xlsx
│ ├── README.txt
│ └── sternberg.psyexp
├── stroop
│ ├── README.txt
│ ├── stroop.psyexp
│ └── trialTypes.xlsx
├── stroopExtended
│ ├── README.txt
│ ├── stroop.psyexp
│ ├── stroopReverse.psyexp
│ ├── trialTypesReverse.xlsx
│ └── trialTypes.xlsx
├── voiceCapture
│ └── voiceCapture.psyexp
└── word_naming
    ├── conditions.csv
    └── word_naming.psyexp
```

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<div class="post-metadata">

**Author:** ![jon](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.psychopy.org/jon/32/22_2.png) [@jon](https://discourse.psychopy.org/u/jon)\
**Post date:** [August 23, 2016, 2:54pm UTC](https://discourse.psychopy.org/t/show-only-part-of-a-video-stimulus-in-psychopy/940/6 "2016-08-23T14:54:04Z")

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Those are the Builder demos, but you’re coding. Coder has its own demos menu. You can also see the Coder demos linked here if you aren’t using Coder:

> **[psychopy/psychopy](https://github.com/psychopy/psychopy/tree/master/psychopy/demos/coder)**
>
> For running psychology and neuroscience experiments - psychopy/psychopy

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<div class="post-metadata">

**Author:** ![Horea\_Christian](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.psychopy.org/horea_christian/32/203_2.png) [@Horea\_Christian](https://discourse.psychopy.org/u/Horea_Christian)\
**Post date:** [August 23, 2016, 2:56pm UTC](https://discourse.psychopy.org/t/show-only-part-of-a-video-stimulus-in-psychopy/940/7 "2016-08-23T14:56:23Z")

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Ok, I was looking under the wrong window.  
Perhaps expectedly so, I found the aforementioned demo under the coding window.

The mistake with my example was that I did not assign the call to a variable; the correct usage would have been:

```auto
aperture = visual.Aperture(win, size=0.2, pos=(0, 0), ori=0, nVert=120, shape='square', inverted=False, units="norm", name=None, autoLog=None)

```

This does what I initially wanted, except that it requires some more roundabout calculations to define the position of the video region of interest.