Why a Video Won't Play on Your Mac (and How to Fix It)

You double-click a video, and instead of playing it, your Mac says something like "The file isn't compatible with QuickTime Player." The file isn't broken, and neither is your Mac. QuickTime, the player that opens videos by default on a Mac, just doesn't understand every video format out there.

TL;DR: QuickTime can't open WebM or MKV files on any Mac, and it can only play AV1 video on Macs with an M3 chip or newer. Apple hasn't said it plans to change that. There are two easy fixes: open the file in a free player like VLC, or convert it once to MP4, which plays everywhere.

If you'd rather convert the file once and be done with it: Video Converter →

Which Videos QuickTime Can't Open

Every video file has two parts. One is the "box" it comes in, which you see as the file extension: .mp4, .mkv or .webm. The other is the way the picture inside is compressed, called the codec. QuickTime has to understand both, and if either one is unfamiliar, it won't open the file.

In practice, it looks like this:

Not sure which chip your Mac has? Click the Apple menu in the top-left corner and choose About This Mac. The chip is listed near the top. Older Macs show an Intel processor there instead.

AV1 is the confusing row. Newer Macs have a special part in the chip just for decoding AV1, and QuickTime relies on it. Older Macs don't have that part, and Apple never made QuickTime play AV1 without it. That's why the same file can open on one Mac and fail on another.

Why the Same Video Plays in Safari

Sometimes a WebM video plays fine on a website in Safari, but the downloaded file won't open when you double-click it. Safari has its own video support built in, separate from the rest of the system. It has played WebM since macOS Big Sur, but QuickTime and most other Apple apps never got the same ability.

Apple hasn't announced any plans to change this. In June 2026, an Apple engineer answered a developer's question about it on Apple's developer forums. With the tools Apple currently provides, the engineer wrote, there's "no supported way" for regular Mac apps to play WebM files. So rather than wait for an update, use one of the two fixes below.

Fix 1: Open It in a Different Player

The quickest fix is a different video player. VLC is free, has been around for more than 20 years, and opens almost any video you give it, including WebM, MKV, VP9 and AV1, on any Mac.

After installing it, right-click the video, choose Open With, and pick VLC. To have VLC open that kind of file every time, select the file, press ⌘ + I, choose VLC under Open with, and click Change All.

IINA is another free option. It handles the same formats and is made only for the Mac, so it looks and feels more like a regular Mac app.

Fix 2: Convert It Once to MP4

A different player solves the problem on your own Mac. It won't help if you want to send the video to someone, play it on a TV or put it on an iPhone. For that, convert the file to MP4 with the H.264 codec, the most widely supported video format there is. It plays on practically every phone, computer and TV.

Any video converter can do this, including our Video Converter. Our step-by-step guide shows where each button is. If you want to know why MP4 is the safe choice, the post on MP4 vs HEVC vs AV1 explains it.

The converted file will often be a bit bigger, because H.264 is an older and less efficient codec. For most videos, the difference in picture quality is hard to spot.

If the Video Came From YouTube

This problem often starts with a YouTube download. YouTube only offers 4K and higher in VP9 or AV1, never in H.264. So a 4K video saved from YouTube can easily turn out to be a file QuickTime won't open.

Our Video Downloader has a setting for this. Go to Preferences, open the Video output tab and turn on use only macOS compatible codecs for MP4 format. There's a trade-off: some videos will then download in a lower resolution, because their 4K version doesn't exist in a Mac-friendly format. If you want the full 4K, leave the setting off and watch those files in VLC.

The Bottom Line

When a video won't open on your Mac, the file is almost never damaged. QuickTime just doesn't read every format, and Apple shows no sign of changing that. To watch on your own Mac, a free player like VLC is the easiest answer. If the video has to play everywhere, convert it to MP4 once and stop worrying about it.