AV1 video will not play on your Mac. Whether that is fixable

A downloaded video will not open in QuickTime, or opens somewhere else and plays like a slideshow while the fans run. The file is probably AV1, and the behaviour is a support question rather than a damaged file.

Confirm what it is

ffprobe -v error -select_streams v:0 \
  -show_entries stream=codec_name,width,height,pix_fmt \
  -of default=noprint_wrappers=1 video.webm

codec_name=av01 is AV1. It commonly arrives in a WebM or MP4 container, so the extension tells you little.

Why your Mac struggles

AV1 is a newer codec, designed to deliver similar quality to HEVC in a smaller file. That efficiency is bought with computational complexity: decoding it takes considerably more work than decoding H.264.

Modern hardware includes dedicated AV1 decoding, which makes playback effortless. Apple silicon added hardware AV1 decoding from the M3 generation onwards. On a Mac without it, decoding falls to the processor, and for 4K content that is usually more than it can sustain in real time.

That produces the two symptoms exactly: applications relying on hardware decoding refuse the file outright, and applications that decode in software play it badly.

Check what you have:

sysctl -n machdep.cpu.brand_string

An Intel Mac has no AV1 hardware decoding at all. An M1 or M2 does not either. M3 and later do.

The practical fix

Use a player that decodes in software, and accept that it may struggle on high resolutions. For 1080p on a reasonably recent machine this is often perfectly acceptable; for 4K it usually is not.

Or convert once and stop fighting it:

ffmpeg -i video.webm -c:v libx264 -crf 20 -preset medium \
  -pix_fmt yuv420p -c:a aac -b:a 192k video.mp4

The result plays everywhere, on any Mac, with hardware decoding. It is larger than the AV1 source, because that is the trade AV1 was making, and if the point is to watch the file rather than to store it efficiently, that is a reasonable price.

For a smaller result on a Mac that handles HEVC, which is every Mac from the last several years:

ffmpeg -i video.webm -c:v libx265 -crf 22 -tag:v hvc1 \
  -c:a aac -b:a 192k video.mp4

-tag:v hvc1 is what makes HEVC play in QuickTime and Safari rather than being refused.

Manatee converts AV1 to a format your Mac plays natively, on the machine rather than by uploading the file, working from a duplicate so the original is kept. Converting is genuinely the right answer here, since no software update will add hardware decoding to a chip that does not have it.

The scaling option

If the problem is 4K rather than AV1 itself, and you are watching in a window, scaling down solves both the decode cost and the file size:

ffmpeg -i video.webm -vf scale=1920:-2 -c:v libx264 -crf 20 \
  -preset medium -pix_fmt yuv420p -c:a aac -b:a 192k video-1080.mp4

A 1080p H.264 file decodes in hardware on any Mac made in the last decade.

Why AV1 is becoming more common

It is royalty-free, which HEVC is not, and it is meaningfully more efficient than H.264. Video platforms have adopted it for exactly those reasons, which is why downloaded video increasingly arrives as AV1 when it used to arrive as H.264.

That trend will continue, and the answer for older hardware will remain conversion. This is the ordinary lifecycle of a codec: efficient formats arrive, hardware catches up over several years, and machines from before the transition need a conversion step in the meantime.

Distinguishing this from a damaged file

Everything above assumes the file is intact. Confirm:

ffprobe -v error -show_entries format=duration,size -of default=noprint_wrappers=1 video.webm

A real duration means the file is fine and the issue is decoding. No duration, or an error, means damage, which is a different problem covered in how to check whether a video file is corrupted.

The distinction matters because the two produce similar frustration and have nothing in common. A file that reports its duration correctly and plays badly is a hardware limitation. A file that reports nothing is damaged, and what can actually be recovered is the honest starting point there.

Questions

Will a macOS update add AV1 support to my Mac? Software decoding, possibly. Hardware decoding, no. That is a property of the chip. On a machine without it, expect software decoding at best, which is fine for 1080p and generally not for 4K.

Why does the same video play on my phone? Recent phones include hardware AV1 decoding. It is entirely normal for a phone to handle a file a several-year-old laptop cannot.

Is converting lossy? Yes, once. At -crf 20 the loss is not visible in normal viewing. Keep the AV1 original if storage allows, since it is the smaller file anyway.

The file plays in a browser but not in QuickTime. Browsers ship their own decoders and do not rely on the system. That is a good sign: it confirms the file is intact and the limitation is elsewhere.