There are plenty of threads on making acapellas, dirty versions, intro versions, and so on using Vegas and FCP. These methods are labour intensive and often involve re-rendering, which can result in a loss of quality

A-Swift and others recommend de-mux and re-muxing with MPEGStreamlip to avoid re-rendering. By accident, I just figured out that if you drop an audio track onto a video playing in QT, the audio is replaced by the track you just dropped onto it! This seems to be much simpler than the whole de-mux, rename, re-mux required using Streamclip.

Has anyone done this? Results? Any obvious drawbacks to using QT for this?