Currently DIKSHA portal allow following file types of videos..
(Please note. you can also use a Youtube video link to create the content).
Please make sure to upload only the supported video files.
You can check the type of file using any online tools. (eg . https://htmlstrip.com/mime-file-type-checker)
1. No, you cannot change he file format by changing/renaming the filename.
2. If you upload an unsupported file, the publishing of the content will fail