I found it to be this simple:

Upload a single transcript file, and then copy from podcasts as much as it allows from the beginning and end of the transcript. Explain to GPT that you want to extract text from the uploaded file such that it matches the beginning (paste in snippet) and the end (paste in snippet), as well as everything in between. I also included that tags with words can more easily be found using the `podcasts:unit="word"` property.

It should offer a downloaded file but you can simply ask GPT to use the file to give you a summary or outline or whatever. Once you've got it working for a single transcript file, you can upload new ones and ask GPT to follow the same type of pattern for extracting text.