I'm also not an expert on this. But usually,
livestreamer can download .m3u8 links.
E.g:
livestreamer "hlsvariant://xxxx.m3u8" best -o test.file.mp4
PS: or do you can post the content of the m3u8 file?
PPS: Do you referring to this:
https://developer.apple.com/library/...Streaming.html