Hello,
PCIbex itself has no such limits, but browsers only support a limited range of video file formats (as listed on the page you referenced) and might have limits on the size of the video files, but that last point will depend on specific configuration points (in general, the limits on size are large enough that they will never be a problem for an experiment)
If your 20+ videos of 4-6s each total to over 1GB, the problem won’t necessarily be the size limit of the browser, but rather how long it takes to download them. With a 720p resolution using the H264 (MP4) compression, a 5s video file shouldn’t be more than 2MB so a total of, say, 30 such videos should represent ~60MB max
I personally wouldn’t participate in a study if I knew it means I have to download more than a few 100MB of resources (and much less if I’m paying for data pro rata)
Jeremy