video file encryption, decryption and player development

Hello, I have several .mp4 video files that my customers use. For the protection of those files. I want two software. 1. First software should encrypt it to some custom format. (The encryption should be simple enough for me to modify. for example inverting every 5th bit) 2. Second software should be a video player with basic functionalities of play, stop, forward, reverse and next file. This player should be able to take the custom format and play the video. The software should be developed preferably using C# and the source file should be given to me. Some assistance may be required from you to help me understand the program so that I can modify to change the encryption and decryption algorithm to maintain the secrecy. I am not sure what should be the right price for such work so I am keeping it open ended.