Joining OxO mp4 files
The OxO 4K produces video files every 3 minutes. This is to prevent loss of all the recording in the event of something unexpected occurring. Joining the files is very easy and thee are may free or low cost apps that will do this.
Online
https://clideo.com/merge-video
https://canva.com/features/merge-videos/
https://adobe.com/express/feature/video/merge
We also like Microsoft's Clipchamp as an easy to use editor - there is a free and a low cost version, both will merge files and edit.
https://support.microsoft.com/en-gb/topic/how-to-combine-videos-94e34901-dc9b-4b0f-8112-2fb72c8f8595
The full version is also included in some Microsoft 365 licences.
Nearly all video editors will also easily join the files.
App
MP4 tools also has a file joiner and can be installed on all platforms. It is a collection of cross-platform free tools to manipulate .mp4 files and can be downloaded here: