Codecs have been a thing on both major OSes, Windows Media Player could open DivX and QuickTime could open MKV. I think they were only limited to videos however.
I think QuickTime 7 had that capability (I remember installing a codec to make it play wmv video) but Apple removed the plugin architecture in QuickTime X.
I think QuickTime 7 had that capability (I remember installing a codec to make it play wmv video) but Apple removed the plugin architecture in QuickTime X.