A few weeks ago I griped about how the default audio player in Chrome is too narrow, and how this makes it hard to seek accurately. I realized yesterday, though, that there's an easy work-around: zooming. By pinch-zooming I can make the seek bar almost the whole width of my phone, which is a big improvement:

It's not perfect: it's not super discoverable and it still doesn't make great use of the available vertical space (showing timing and seeking at the same time would be nice) but I'm very happy I've found this.