Q: During Zoom video calls, my screen image follows my actual movements very slowly. If I move my head or speak, there's sometimes a delay of two seconds or more before it happens on my screen. (This didn't happen during a Microsoft Teams video call.) Other people in the Zoom meeting say they don't have the same problem. I've updated Zoom and my Windows 10 PC, but nothing helps. What's wrong?

Phil Morton, Eden Prairie

A: The possible causes include your home network, your internet connection or the Zoom video-calling service — or maybe all three.

There will always some time-lag problems on video calls due to signal processing and internet congestion issues (Microsoft Teams has also had lag time issues.) But your relatively long Zoom delays, and the fact that others on your Zoom call don't experience them, are unusual.

The first thing you should do is check the speeds of your internet connection (determined by your internet service provider) and your home network (determined by its connections).

Test your internet speed at Speedtest (tinyurl.com/y3kon7nl), nPerf (tinyurl.com/y5utxtf5) or Comparitech (tinyurl.com/ybww67jl).

For one-to-one video calls, Zoom requires that you have 0.6 megabit upload and download speeds for basic video, and 1.2 to 1.8 megabit speeds for high-definition video. Group video meetings require higher speeds (see tinyurl.com/hpjtc98).

Adjust your home network. If your Wi-Fi is slow, it can add delays to a video call. Try using a wired connection between your computer and modem to speed things up.

If you must use Wi-Fi, move your computer closer to your Wi-Fi router to reduce time lag (Wi-Fi signal strength is weakened by distance and barriers such as walls.) Alternatively, you can buy a wireless router with a stronger signal or a Wi-Fi extender that will expand the range of your existing router.

If the lag time is caused by Zoom, there are some things you can fix and some you can't.

You can adjust the time of day you use Zoom. The service has been experiencing high demand from people working at home during the day. As a result, you might experience less lag time if you use Zoom during off-peak hours.

Unless you pay for Zoom service, you can't maximize the way Zoom connects international video calls. As a result, during a free international call you might be much farther from the Zoom regional data center being used than the other participants are. That could cause time lag for you, but not others (see tinyurl.com/ycqgnz2v).

Q: When I watch movies on my 55-inch Samsung smart TV, I sometimes get black bars at the top and bottom of the screen. Why doesn't the TV reformat the images to make them full screen?

Dwight Pollard, Andover, Minn.

A: The TV is opting to give you a nondistorted picture, which works in your favor.

Many movies have been filmed in different picture shapes, called "aspect ratios." If a movie's aspect ratio doesn't fit your TV screen, you can either watch it normally on a partial screen (with black bars) or have the picture stretched or cropped to fit your full screen (see tinyurl.com/y9q35czu).

E-mail tech questions to steve.j.alexander@gmail.com. Include name, city and telephone number.