[marhutchy]

Can't MC arrive at a source by reading the media codec, without having the source's name within the filename?

No, Source isn't exactly what is in the media's stream info, but rather where the media was sourced from.
ie: Screener, DVD, Pay-per-view, HDTV, Bluray etc.
Some of the above can have the same resolutions, but from completely different media, and these are usually found in the filename.

That's true.
Most of my movies are BRRip, so I can set them manually with ease.