Combine audio and video streams from different files. This can be useful when you want to add multi-channel audio (eg. ac3) to a video file for playback in multimedia installations.
Download the latest MuxTool.zip here.
Drag and Drop
Doesn't encode, just rams the files together so the quality shouldn't suffer.
It isn't very intelligent, so if your source files are strange, it may not work for you.
Binary available for macOS. You should be able to build binaries for other platforms easily by cloning the repo using npm to install the dependencies (including the appropriate FFmpeg binary), and building it with the electron-packager. There is a bit in the renderer where it plays the macOS sound on completion which you may need to take out.