Mac slow during video calls? How to find the culprit

A Mac gets slow during a video call because the call itself is hard work, and anything else running in the background has to share what is left. The usual culprits are a browser with many tabs open, a sync or backup that started at the wrong moment, and an app that was already busy before the call began. The fix is to find what is competing with the call and quit it or slow it down, in that order.

Below: why calls are demanding, how to see what is competing, what to quit first, and how to give the call more room without closing everything.

Why a call is hard work

A video call does at least four jobs at the same time, and none of them can wait.

• The camera. Your Mac captures video many times a second.
• Encoding. That video is compressed so it can travel over the internet. Compressing video takes real work from the processor or the graphics hardware.
• Decoding. Everyone else’s video arrives compressed and has to be unpacked and drawn on screen, one stream for each person in the grid.
• Audio and the network. Your voice is captured and sent, theirs is played, and the connection has to keep up in both directions.

The key point is that a call has deadlines. If a web page loads half a second late, you barely notice. If a video frame arrives half a second late, the picture freezes and the sound breaks up. That is why a call exposes a Mac that is only slightly overloaded: the same load that is invisible in a document is obvious in a call.

Features add more. Blurred backgrounds, filters and reactions use extra processing for every frame, and a shared screen adds another stream on top. If a call runs fine with your camera off and stutters with it on, the camera work is the part your Mac is struggling with.

Browser calls live in tab processes

Many calls run in a browser tab. Browsers split every tab into its own process, so a call in a tab is one of many processes the browser runs, and the other tabs are running alongside it. A few things follow from that.

• A call tab and a heavy tab (a spreadsheet, a video site, a web app that refreshes itself) compete for the same processor.
• Safari’s pages run in processes that Foreman shows as “Web content”, next to “Web networking” and “Web graphics”. Other browsers have similar helpers. All of them belong to the one browser.
• Closing a heavy tab stops its work. Leaving it open in the background does not.

So before a call, close the tabs you do not need. It is the single easiest change, and it often helps more than anything else. If you are not sure which tab is heavy, how to tell if one browser tab is slowing down your Mac shows how to find it.

Find what is competing with the call

You want to know what else is using the processor while the call runs. Two ways to see it.

With what macOS gives you. Open the Force Quit window with Option-Command-Escape to see which apps are open and whether any is marked as not responding. It does not show how busy anything is. For numbers, open Terminal and run top -o cpu, which sorts processes by processor use and updates once a second. Press q to leave it. The names are the technical ones, so a browser may show up as several lines, but the top three or four lines will tell you what is busy.

With Foreman. Foreman is a Task Manager for macOS. Open it with Control-Shift-Escape, which works from any app, so you do not have to leave the call. The Processes page lists apps with their helper processes added up under each one. Sort by CPU and the busiest app is at the top. The same page has a GPU column, which matters in a call because video work can use the graphics hardware. If you screen-share, look at GPU as well as CPU.

What you are looking for is an app that is high while you are not using it. Common ones:

• A cloud sync catching up after you saved a large file. In Foreman, iCloud Drive’s sync shows as “iCloud Drive” (bird), and the link between Finder and cloud storage such as Dropbox as “Cloud files” (fileproviderd).
• Spotlight indexing after a big change or update. It appears as “Spotlight indexing” and “Spotlight file reader” in Foreman. It is normal and it finishes, but it will compete with your call until it does.
• Photos analysing your library. It shows as “Photos analysis” and “Media analysis”, and it runs mostly while the Mac is idle.
• A backup. “Time Machine backup” is the name to look for.
• An app that was already busy, such as an export, a build or a game left running.

Several of these are parts of macOS. Ending them rarely helps: they are doing real work, and many simply start again. Let them finish, move the call if you can, or slow them down as described below.

What to quit first, and what to slow

Work from the cheapest change to the most disruptive.

1. Close browser tabs and windows you do not need. This is the biggest win for browser calls.
2. Quit apps you are not using. Use Command-Q, which lets an app save its work. Only force quit if it will not close.
3. Turn off video effects. Backgrounds and filters cost processing on every frame. If things improve, you know where the load was.
4. Turn off your own video for a moment if the problem is only for large meetings. It cuts the encoding job.
5. Switch to Wi-Fi at a closer spot or a cable. If the picture freezes but the Mac itself is not busy, the network is the likely cause, and no amount of quitting apps will fix that.

For the apps you want to keep open but do not need during the call, Foreman has Efficiency Mode. Select the app, click the Efficiency Mode button in the toolbar (or press Shift-Command-E), and while that app is in the background it runs at background priority and is held to about a quarter of the processor time it would take, working in short bursts. When you switch to it, or while it plays sound, it runs at full speed again. It is remembered for that app until you turn it off. It also works on macOS’s own background processes that run under your account, such as Photos analysis, Media analysis and iCloud Drive, which is useful when one of them gets busy in the middle of a call. Spotlight indexing and Time Machine backup run under the system’s root account, so Foreman does not offer it for those. How much it helps depends on how busy the Mac is, so treat it as a way to give the call more room, not as a guarantee.

If an app will not let go of the processor and you want it fully out of the way, Suspend freezes it where it is, using no processor, until you choose Resume. Foreman asks first. It is not offered for parts of macOS that would freeze the Mac. Suspend a heavy app mid-job only if you are sure you can resume it, because the app does nothing until you do.

After the call

A call that stutters once is not always worth investigating. A Mac that stutters in every call is worth a closer look.

• Check how much of the drive is free in System Settings under General, then Storage. A nearly full drive makes everything slower.
• Look at what opens at login. A Mac that starts with ten helpers already running has less to spare. How to stop apps opening at login on a Mac covers it.
• If memory pressure stays high all day, a call will feel it first.

Foreman costs $12 once and is free for 24 hours, so you can try it on your next call. Open it before the call starts, glance at the top of the CPU column, and you will know within a minute whether something other than the call is eating the processor.