Exclude file extensions - C0D3D3V/Moodle-DL GitHub Wiki
You can exclude file extensions. However, this only affects files stored directly on moodle, not external links (and not extensions that require a cookie).
To exclude files with certain extensions, an entry like the following must be added to the configuration file:
    "exclude_file_extensions": [
        "png",
        "mkv"
    ]
(Don't forget the comma before the entry)
This would not download all files ending in .png or .mkv.