I know it doesn’t accept FLV, WEBM, or MP4’s.
Please edit your question to provide specific audio / video stream codec detail. FLV / WEBM / MP4 are all container formats that can use a variety of different codecs. Codecs are where support is required. Also indicate your operating system and LO version. Thanks.
Please have a look at:
Unfortunately, Libre Office does not seem to support its own suggested file types.
Also, answer does not help, for I have Win XP.
Insert > Movie and sound and check the File types drop-down box.