This is something I've never quite understood, but have always wondered. Forgive my basic knowledge here, but I've tried to research this without a specific answer as to what is going on.
When I convert from an .MTS file to ProRes422 HQ, the file get's huge. Why is that? Where is that extra data coming from if it's not there to begin with? i.e. higher bitrate. I understand the codec has a standard bitrate it will always maintain, but why do it if the original file bitrate is so much lower?
For example, a stock GH2 mts for me streams at about 22 Mbits/s, I convert it to ProRes422 HQ, that same file is now playing at 216 Mbits/s. - With no discernible image quality difference.
What is going on in the codec that makes the file so huge? Other than workflow issues, why would you want to transcode from MTS? Does converting it to ProRes (or another codec) 'Unpack' the data in a more efficient way?
Why not use something like ProRes422 LT if you're starting from a much lower data rate like a native MTS file provides?