when i press "upload file" and pick the video i want it doesn't show it even though it's really small (it's nine seconds)
If you mean sending a film to the project resources, the length of the film is not important, only the format and size on the disk. 9s of a 4k film can take up something like 100MB, which is too much. Compress your film, there are free websites for this.
Upload to where? If you want to upload it to assets, there is a 1MB (or at most 5MB) limit that can be bypassed by using 7-Zip or WinRAR. However, the aia size cannot be larger than 30MB (on the main AI2 server).