The default permissions for the recording are set with the person who made the recording as the owner of the video and this is stored in their OneDrive. The Nexus365 users who attended the meeting or were on the meeting invite are given view-only access to the recording.
External or guest meeting participants will not have access to the recording automatically. You can share the recording with external or guest meeting participants and with internal Nexus365 users who weren't invited to the meeting by sharing the recording like you would share any other file in OneDrive for Business.
If you were not the person who recorded or organised the meeting, you can still share the recording with people who weren't invited to the meeting. However, the meeting organiser or the meeting recorder will need to approve your share action before other people will get access.
Channel meetings
If your recording was in a channel meeting then the recording is saved in the files tab for the channel and everyone who is a member of the channel will have permission to edit and view the recording.