Thumbnail is not generating for video assets

[bshovon]

versions

• SlimerJS: 1.0.0
• Firefox: 59.0
• Operating system: "Ubuntu 20.04.4 LTS"
• VERSION_ID="20.04"
• Setup : AWS Docker containerized

Steps to reproduce the issue

Generating dynamic snapshot with following command:
xvfb-run -a /plugins/slimerjs/slimerjs /plugins/slimerjs/createThumbnail.js Test-Image.png 1280px*720px 1500 debug=true
Note: Snapshot generation is working fine with Images. It's failing only for video assets.

Actual results:

Dynamic thumbnail generation is not proper for video assets, blank screen/ video player loading Icon is coming in the dynamic screenshot screen
Error log:
[DEBUG] network: resource #55 response in error (3): 99 - an unknown network-related error was detected (NS_ERROR_UNEXPECTED)

Expected results:

Dynamic snapshot should contains actual video poster Image.