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Some participants unable to load Pavlovia resources

URL of experiment: https://run.pavlovia.org/Mi_Lab/engagement-in-a-virtual-world-cb1-v2/html

Description of the problem:

I’m running a Pavlovia study which involves playing a ~350mb, .mp4 video followed by a brief memory task. Numerous people from my lab piloted the study from a variety of locations, countries, devices, and browsers to ensure participants wouldn’t encounter issues downloading the video file at the beginning of the experiment. Everyone who piloted it was able to download all resources in under 3 minutes, except for those using Safari.

When we launched the study, about half of the participants were able to download everything just fine. However, many participants contacted me saying they were unable to download the resources. One participant said it took them over an hour for the files to download, and another got the following error:

Engagement in a Virtual World CB1 V2
unable to download resource: EVW_CB1_2.mp4 (FILE_LOAD_ERROR)
Try to run the experiment again. If the error persists, contact the experiment designer.

I’m not sure what is going wrong for the participants who are encountering this problem, and I cannot replicate the error. I confirmed with the folks who had issues that they were using Chrome, Firefox, or Edge (all which we have had success with). We have tested the experiment on both fast and slow internet connections (including VPNs) and have not had any problem downloading the resources using the appropriate browsers.

Are there any known issues related to this error? Is it possible that this could be caused by multiple participants downloading the files at the same time?

I am pretty new to PsychoPy and Pavlovia so anything helps. Thanks very much for your time!

Hi again-- just an update here: this has continued to be an issue and it is still very sporadic. Some participants do just fine while others run into trouble, and there doesn’t seem to be any rhyme or reason to it. Any help would be great!

I’m not sure why this would be happening. Fetching 300 mb of files is well withing the server’s capacity and it has been perfectly capable of handling thousands of requests at a time - I think i’t unlikely that the issue is at the server end. Do you know about your participants network speeds? My guess is that it’s more likely at that end, depending on how you’re recruiting.

We will be working on a streaming option, so that the movie doesn’t download in one go at the start but for now the only solution I can see is that you try and reduce the movie size. What resolution are you currently using?

I had a similar issue this weekend (unable to download an image FILE_ERROR_LOAD). After running 7-8 participants successfully, one got this error. As @jon says, I also suspect it’s related to participant’s network speeds.

Hi Jon, thanks for getting back to me.

The video is 720p. We have already reduced the resolution once before launching the study. Reducing it further has been something I’ve considered, but I’m really hoping I can avoid it as I want the contents to be as clear as possible.

I unfortunately don’t know about our participants’ internet speed, but even with relatively slow internet (75mbps) the single file should theoretically download in under a minute. Considering the fact that about half of our participants thus far have been completely unable to download the file (some have waited over an hour), I would be surprised if that many people have internet this slow. I believe it would have to be under 10mbps to take that long!

I have also noticed that I get emails from participants encountering issues in clusters which seems strange to me, but could be coincidental. When our lab tested it out, about 15 people tried it and the most likely difference I can see that could explain why none of them had issues is that they all did it at separate times (again this could be coincidental). I know that one of them tends to get slow-ish connection (speed test indicates ~80mbps) and she had no issues.

Regardless, if you aren’t sure of anything else that could cause it, I’ll play around with reduced resolution and hope things improve.

How are you doing recruitment? MTurk, Prolific or something else?

I think you might overestimate the quality of some people’s broadband. “Relatively slow” internet being 75 mbps is I think optimistic and/or country-specific. Someone on a mobile device that isn’t close to a transmitter will drop way below that. DSL (the phone technology that most people used before fibre optic cable, and which I imagine it still in use in some places) had speeds of 128kbps - 9mbps. So 10mbps is not that surprising for occasional users.

I’ve used both Prolific and my university’s subject pool for recruitment. When I used Prolific, I limited sign-ups to Canada, the U.S., and the U.K. Participants from both platforms encountered issues.

Good to know about internet speed-- thanks! I’ve decreased the resolution of the video and will give that a try in our next wave of recruitment.