It's conceivable that this is a limitation of the encoder. Try a different one, such as MPEG4. Click the blue Default Quality/Filesize link to see the choices.

If that makes no difference, please upload the file in question to a free server, such as Google Drive or MS OneDrive, get a shared (public) link, copy the link and paste it here or to me in a Private Message via the mail envelope in the top-right corner of this forum. When using Google Drive, if necessary change "restricted" to "anyone with link can view."