$ mkchromecast -s --video -i "/path/to/file.mp4" --encoder-backend ffmpeg (--seek 00:00:00)
$ mkchromecast --source-url http://commondatastorage.googleapis.com/gtv-videos-bucket/sample/BigBuckBunny.mp4 -c mp4 --volume --video
will download video to pc before streaming
$ mkchromecast -y https://[site] --video
also use mkchromecast --help for more info