I solved the issue (for now). My previous post was not 100% correct - the steps worked, but only because they forced me to use the hdmi output, which was apparently not affected by the original issue. I could verify this afterwards. Anyhow, the eventual solution was to find the previous Realtek drivers, and install those. I did not realize these were available for download from the Dell website - I did not find them at first. Note: I also configured Windows Update not to automatically update drivers. So here's hoping that Windows Update will, in fact, honor that, and leave those older, working Realtek drivers intact.
Since about a week ago, an issue started on my Dell XPS 17 9700: starting any video or audio file is delayed for about 10 seconds, and then it starts. In the case of video, depending on the app, it can be worse, with video and audio being unsynchronized for 10-20 seconds until it settles. All of this is regardless of whether I have the media file locally, or I'm streaming it. So after a while I figured it must be a driver issue. So I downloaded the most recent audio drivers for my laptop. Tried installing it, but it got stuck on uninstalling the previous one. Okay, I restarted, and the installation did not continue - but my issue was solved! Hurray. Unfortunately, within a day, Windows Update had updated drivers automatically, and the issue was back. So I tried the Dell Realtek drivers installation file again that I had already downloaded, and this time it uninstalled, restarted, installed, restarted, successfully. However, the issue is still there. So at this point, the only thing I can do is uninstall the drive and just hope Windows won't put them back too quickly. What is a better solution?
Recent Realtek drives don't work well