Sending video via MMS requires the video to be compressed pretty severely, since MMS has a filesize limit for attachments, and for most carriers, it's about 1 MB. For a video of any considerable length to be compressed down to 1 MB means a huge loss in detail. You're better off uploading the video to your Google Photos in the cloud or YouTube, and sharing the link privately with the recipient. Or use a different messaging platform like Telegram.