Many people are frustrated that YouTube videos stop playing - or freeze or pause - after a few seconds. The videos also play for a short time without sound, no matter what you do to your volume settings. See also: How to download YouTube videos
How to unfreeze YouTube video
Check your broadband
First, make sure it's not a slow internet connection causing the problem. If other people in the house are watching Netflix, playing games and doing other things which could be using up a lot of the bandwidth, this is a quick answer to the problem.
You can also use broadband speed checkers such as Speedtest.net to quickly find out how fast your broadband is currently running. You'll want at least a couple of megabits per second for a single stream of HD video, and more if several people are using the connection at the same time.
Restart your device
If it's not that, try restarting your PC, laptop, phone or tablet. This fixes a surprising number of problems, but is often forgotten in the heat of the moment when you're experiencing a problem. For phones and tablets, hold down the power button until you see an option to restart or power off.
Try a different browser or app
Similarly, try watching the YouTube video via a different browser or app, just in case it's the software causing the issue.
YouTube itself now uses HTML5 as the default way to play videos, having dropped Flash back in 2015. So it shouldn't be Adobe Flash that's causing your problem. But just to double-check that this isn't the case, head to Control Panel > Programs and then Uninstall a Program. The list is presented in alphabetical order, so you should see Adobe Flash player near the top if it's installed.
Since virtually nothing uses Flash any longer, there's no harm in uninstalling it, and you'll actually protect your PC from its security risks by removing it. (You can always reinstall it again if you need it for something.)
If your YouTube problem goes away after this, it was almost certainly Flash causing the issue.
Problem not fixed? Read on... (and be sure to watch the excellent Project Binky series on YouTube)
Firefox and Chrome YouTube tips
In Firefox click the three horizonal lines at the top right, go to Options > Advanced > General.
In the second section called Browsing uncheck "Use Hardware Acceleration when available".
Unchecking this doesn’t seem to have any big impact on Firefox or video performance. Similarly, though, if Hardware Acceleration is not ticked, try enabling it.
It's almost identical in Chrome. Click the three dots at the top right, then choose Settings. Use the search box and type 'hardware'. Uncheck "Use Hardware Acceleration when available".