Easy way to switch containers? (MKV to MP4, specifically)

[Espio]

I want to change the container of a video without actually re-encoding the video so I'm wondering if there's a program that will demux the video and audio in one container and remux it into another container.

[Ranguvar]

Look up MP4Box (MP4 muxer, YAMB is a good GUI) and MKVtoolnix (bunch of tools for working with the Matroska container (MKV)). You should be able to do what you want quite easily.

[stax76]

StaxRip beta can do with little user input, it can also batch remux.