Within the same track, you can simultaneously play audio, midi, video or even picture* files.
Items can be from different channel counts (mono, stereo, multichannel), sample rates, bit depths or compression types (mp3, flac, wav, etc.). REAPER will convert and play them in realtime to the project’s settings, without converting the source files destructively.
* Pictures will appear as steady pictures in the video rendering window, for the length of the item.
Each track contains up to 64 channels, which means you can work in 63.1 surround if you wish to! Any track can be a buss.