Hi there,
Unfortunately, if you have video files you grabbed in the past, you likely can't decrypt them since the keys for your stream are long gone, discarded, or changed. Likewise, it probably isn't practical for me to spend time to explain how some of this works. Unless your a software developer it won't do you any good, and if you are a software developer (of sufficient skill/knowlege) you'd already know the general process anyway. (^_^);