Hi Nick
What error message did you get?
Actually, video file can be uploaded to a SharePoint document library by clicking the “upload” button rather than switching to explorer view.
If you fail to upload the video file into the library, there are a few things to be check.
1. Please check the “Maximum Upload Size” setting in Central Admin site -> Application Management -> Web Application Settings. By default, the maximum uploaded size is 50MB. If the combined size is larger than this setting, no content, single file or group of files can be uploaded.
2. Please confirm whether .avi file has been blocked by SharePoint. You should go to Central Admin Site -> Operations -> Block File Types. If a user tries to upload a blocked type file, an error will happens.
Best Regards!