[Question] What iDCT Algorithm(s) Is Utilized for MPEG-2 Videos?

[DeadSkullzJr]

As the title implies, I am looking to know what iDCT algorithm(s) lossless-cut is utilizing to decode and encode MPEG-2 video sources. Long story short, I made a request to another developer on integration of any possible lossless decoder / encoder iDCT algorithm of sorts for MPEG-2 sources. I am working with DVD sources and was wanting to preserve the quality as much as possible, sadly everything that decodes and encodes into the MPEG-2 format always causes destruction due to being lossy. This developer knows a lot about how these algorithms work considering their software already has a few different options, however they kind of threw the task of researching and finding a viable algorithm onto me and give them source code for it. While I do have a lot of experience with video encoding and such, I am obviously not all knowing about every aspect of how it all works, let alone all the available options. I have no idea what sources to look at for reliable iDCT algorithms, hence why I am asking what algorithms this solution uses, so I can at least get an idea on what I can research into. FFmpeg I know is utilized, but I haven't figured out what iDCT options it has yet either... I need some help if at all possible.