i know that is possible only audio and text
If you keep what you import private, you can import anything you want.
You can definitely import YouTube videos, you can also just import audio files and nothing else or even just text files. You can do what you want as long as you don’t share your imports as lessons in the library. If you don’t make them publicly available to everyone you won’t be earning points on them and won’t be making money on them, they will be considered as private content.
You said you know it is only possible to upload “audio and text” but many people just upload text privately to create LingQs and build their vocabulary.
If on the other hand, you want to earn cash you can be a content provider.
Content Providers Contributing to Public Imports:
Content providers at LingQ (and anyone can choose to be a content provider), either get permission from copyright owners to add material to the library (from which they can earn money every time a user clicks on the uploaded content) or make their own content, all of which must include audio and text.
You earn points for uploaded content in the library if the content is popular (lessons opened by users lead to points leading to cash), kept that in mind that the points you earn may not be enough to cash. You have to upload lots of lessons to make it worth your while, if earning money is your goal.
Hope this answers your question and helps you understand what is allowed and isn’t allowed.