Why have the SRT files? I use VLC or other video players to create a playlist and randomly loop the videos on a big screen in our office for all our developers to watch. You just need to drop the SRT files with the same name as your MP4 files downloaded from Apple in the same folder. Make sure the file names are the same. VLC and most video players will just pick it up and display the subtitles correctly.

WWDC 2019 files are processing now.

If you need to download the videos and PDFs, check out this project https://github.com/ohoachuck/wwdc-downloader