How ID3 metadata is extracted in LIVE streaming?

I am trying to perform ad insertion using ID3 metadata and Wowza as can be found in: https://www.wowza.com/resources/webinars/streamtalk-jw-masterclass-session4 In this webinar they do not address the time precision of the ad insertion and I am interested in frame precision. So, I was wondering how JW Player onMeta event works when detecting the ID3 metadata. As the metadata is stored in the header of the HLS chunk, I can get the ID3 before inserting the ad, isn't it? And if so, how can I play tge ad in the correct timecode? I am still reading the information and maybe you have some tutorials facing this topic. Other question is how to get the timecode of the ID3 metadata. I am thinking in defining it as text to be inserted in the ID3. Thanks!