[minor improvement] make it clear that data paths cannot contain whitespaces in dataset video encoding

[tlpss]

The video encoding in the dataset uses ffmpeg through a subprocess call.

This imposes a constraint on the file paths: they cannot contain a space as this is considered a separator by the CLI parser.

This currently fails silently. I believe we can make the framework easier to use by either:

• epxlicitly checking and raising an Error if the paths contain whitespaces
• encapsulating the paths with quotes to deal with the issue

best solution might depend on the assumptions made throughout the framework about path naming