Do you inject metadata when making spatial audio files, or when combining those files with video?

[Ric de Mowbray]

Just looking through youtube spatial audio requirements and not sure as to whether it's my responsibility when making the audio files to inject the necessary metadata, or if that happens when the audio gets encoded with the video. With something like FB encoder or Media Encoder? Seems .mp4 is preferable for the audio, is it a case of converting after, or is a WAV also acceptable?