The animated export plays your file once, in real time.
A PNG or SVG comes out instantly. The animated video is a different thing: it draws the waveform reacting to the actual audio, frame by frame, while the file plays — so a two-minute clip takes about two minutes to export, the same real-time bound Subtitle Studio and Auto Subtitle both disclose. There is no way to record it faster than it plays.
The animated file is WebM (VP9 + Opus, typically) with the audio re-encoded, not copied — a real, usually inaudible generational step, same as every other MediaRecorder-based export in this build.