HLS steams with many subtitle variants are broken
https://pubads.g.doubleclick.net/ondemand/hls/content/2503702/vid/KaitlynSadtler_2018U/CHS/streams/c158db81-3bf7-4d01-921b-0f0ef58e4879/master.m3u8. You will notice that startup is very slow, since it's going through 27 subtitle tracks ahead-of-time and creating streams for them.
Then we miss a lot of data and start 10-15 seconds into the video. At which point desync between the audio and video has started and the video is hard to watch.
This was discovered in WebKit when browing TED.com. See also #585 for another issue in the TED HLS streams.