ffmpegConvert mp4 to avi

Since avi and mp4 are containers, not codecs, we simply copy video/audio streams:

ffmpeg -i in.mp4 -c:v copy -c:a copy out.avictrl + cyoutubegithub

`ffmpeg` name of the package to install	`-i in.mp4` input video file
`-c:v copy` just copy video stream from input to output	`-c:a copy` just copy audio stream from input to output
`out.avi` resulting file