Better understanding about QuickTimeMov purpose

[puttin]

Hi, I have few questions about the QuickTimeMov.swift & JPEG.swift main purpose.

1. Is that these two class main purpose is add the assetIdentifier?
2. Why the assetIdentifier so important? Is that main for Photos to recognize them as a live photo?
3. What is the purpose of StillImageTime? Is that for Photos to judge where the still image position in the video file?

I find some demos on GitHub using your QuickTimeMov.swift, but the file has mzp & LoveLiver headers. So I come here. Thanks.