Always we need something which simplify our task/job. Here I have attached code which can convert video using ffmpeg.
# ffmpeg -i /path/to/inputfilename /path/to/outputfilename
Example: ffmpeg -i /usr/local/public_html/abc.flv /usr/local/public_html/abc.mp4
It will convert abc.flv file to abc.mp4 without any codec(video/audio)
You can also check other formats also using following command:
# ffmpeg -formats