AAC-LC (Low Complexity) is the baseline, most widely deployed profile of AAC, and in practice the audio in the overwhelming majority of MP4 video files — YouTube, Netflix, Apple, and almost every OTT service. It deliberately omits the heaviest coding tools for a good balance of quality, decode cost, and universal hardware support, and it sounds transparent to most listeners around 256 kbps stereo, very good at 128. When someone says a video is 'AAC' without naming a profile, they almost always mean AAC-LC. The HE-AAC variants extend it for low bitrates by adding SBR and Parametric Stereo on top of an LC core.
