@LiamMrk You need to do a number of things before you upload the mp4 file with the Media uploader.
- Check that your blog can upload MP4 files. SOmething like Network Admin : Settings -> Network Settings : Upload File Types -- mp4
- Check that you have sufficiently large max upload file size set. In the Network Settings above 'Max upload file size: 131,072' = 128Mb.
- Open the raw video with a compressor such as VideoMonkey (Mac only) to compress the video to mp4/mv4. I compressed a 256Mb capture down to 18Mb at 1280 x 720.
- Upload the compressed mp4 with the media uploader
- To display in a blog post or page you'll need to use a video display plugin. The link above gives you a list. I use MediaElemnts.js but I have to type in the shortcode manually -- there's no editor icon to auto create the shortcode
FFMPEG is an open source system for converting and crunching videos. You won't be able to run this on a normal web site that you'd get from a provider. Use VideoMonkey or similar on your home machine. I believe Videomonkey uses the FFMpeg code.
There's a lot involved in massaging and displaying video -- maybe you should upload to Youtube ?