It's not quite "realtime analysis", but... MP3 compression works by FFT-ing the audio stream, which is something that has to be ingested sequentially. It's no

It's not quite "realtime analysis", but... MP3 compression works by FFT-ing the audio stream, which is something that has to be ingested sequentially. It's not realtime since the encoder does it much faster than realtime, but it is doing sequential analysis of the file. Usually a high quality encoder does multiple passes of the file to better fit it's FFT with the source material.