[API Question] Undestanding transcoding options while using API

[avdept]

Hey folks, so I'm using Jellyfin api for JellyBox player, however I'm kinda stuck with making proper calls to streaming endpoint and understanding query params. So there are these params

'TranscodingContainer': 'm4a',
 'AudioCodec': 'm4a',
 'Container': 'mp3,aac,m4a|aac,m4b|aac,flac,alac,m4a|alac,m4b|alac,wav,m4a,aiff,aif',

while I understand TranscodintContainer and AudioCodec params, what is Container, and what's the format of its value?
I'm using endpoint Audio/:id/universal

What I'm trying to achieve - ensure iOS devices can play lossless audio, assuming my app doesn't support playing FLAC, however do support ALAC.

Need your guidance on correct api usage.
Thanks