Video dumping doesn't seem to work

[ian-h-chamberlain]

Example: https://github.com/ian-h-chamberlain/test-runner-3ds/suites/14871964728/artifacts/846943789

The output .webm files appear "valid", but don't play in VLC. Maybe we can just try different video formats and see if it works better?

Also, it might make sense to see if there's a way to print both to GDB and to the console for these, although really the video dump is more likely to be helpful with actual graphics and/or running examples.