How can we make video converter....???

Answer 1

Familiarize yourself with the different compression methods first and if I were you, I would start with audio first

Answer 2

Install a codec system in your server and read the documentation of the codec. Especially the parts that declares how you use the codec programmatically.

Answer 3

Brut-force approach is to decompress and then compress to another format. But a more eloquent but more difficult way is to convert without decompressing