It will use an MP4 container with either AAC or ALAC codecs. Additionally, there will be some metadata specifying details about compression for each stem to mimick mastering when they are mixed differently. It seems to be the responsibility of the program playing the Stems file to apply the compression on-the-fly.
Here is a video from NI talking all about Stems: https:/ /www.youtube. com/watch? v=MntkrfNAQ6w
It will use an MP4 container with either AAC or ALAC codecs. Additionally, there will be some metadata specifying details about compression for each stem to mimick mastering when they are mixed differently. It seems to be the responsibility of the program playing the Stems file to apply the compression on-the-fly.