Stimuli guidelines

What are stimuli?

In short, stimuli are what you are testing, this can be anything from a static ad to various taglines. Your stimuli are the input for your research.

Best Practices

When it comes to the solutions offered through Zappi, there are a variety of questions that come up around the stimuli necessary for a successful test. Below you will see all of the formats possible for acceptable stimuli, should you be seeking more information around a project you are launching, please check the article for that specific solution. 

Regardless of format, it is important to limit the text heaviness of stimuli, since this could make it harder for respondents to read on mobile. 

File Format Guidelines


  • Format. MP4, MOV
  • File size. We recommend that you do not try to upload files greater than 100MB.
  • Resolution (pixels). 1280x720 This is an aspect ratio of 16:9, which is the resolution of a normal widescreen TV. Youtube and Facebook as standard use 16:9 also. Both Youtube and Facebook recommend that uploaded videos are in MP4 format for best display.
  • System limitations. Apple encoded video (aka Quicktime) cannot be processed by our transcoder. The longer the file, the longer the video takes to transcode.

Using the program Handbrake is helpful if the file format is not suitable, download it here.


  • Format. JPG, PNG (RGB color format only - CMYK not supported)
  • Resolution (pixels). Ideally nothing over 800 high, but the width can be up to 1366.
  • For in context. Facebook right column = 300x157. Facebook newsfeed = 500x282. for big screens, this may stretch slightly, for small it may squish, but this is a comfy middle ground.
  • System limitations. The larger the file, the longer the image takes to display. This means for respondents with slow computers, or slow internet speeds, have the capacity to drop out.


  • Format. Only compatible with AAC or MP3 format
  • Length. Ideally not longer than 2 minutes. The longer the file, the longer the respondent has to listen, increasing the chance they will drop out.


  • Check out the guidelines and best practices to test animatic stimuli
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