What is an AVIF file?

AVIF is a container: a wrapper that holds streams encoded by something else. It stores a grid of pixels, so enlarging it past its own resolution softens it. It is used for the web and handing a finished file over.

The extension is .avif, and the full name is AV1 Image File Format. Both matter less than what the file can hold, which is what the rest of this page is about.

Alliance for Open Media published it in 2019. The specification is AV1 Image File Format.

Age is worth knowing here for one practical reason: the older a format is, the more programs have had time to learn it.

It is published in full, so anyone can implement it from the document rather than by inspection, which is why it turns up in so many programs and why files written twenty years ago still open. A published specification is not the same thing as a royalty-free one: where a format wraps a codec, the patent licensing is a separate question the standard does not settle.

AVIF stores its content exactly. Saving it again changes nothing, so it can be opened, edited and re-saved as often as you like without accumulating damage — which is what makes it a working format rather than a delivery one.

AVIF carries an alpha channel, so a logo keeps its soft edges over whatever sits behind it instead of arriving in a white box.

AVIF can store an animation rather than a single still. That is worth knowing before converting one: a target that holds one frame keeps the first and drops the rest, usually without saying so.

Up to 12 bits per channel. It can work in RGB, YCbCr, the model video and JPEG compress in and wide-gamut colour.

More than eight bits per channel is what stops a gradient from stepping when it is edited, which is why it matters in a working file and rarely in a finished one.

AVIF cannot describe an image larger than 65,536 pixels on a side. That is far beyond an ordinary photograph and well within reach of a stitched panorama or a high-resolution scan, which is exactly when people meet it.

It usually holds AV1. This is the distinction behind most "why will this not play" questions: two files with the same extension can contain entirely different encodings, and a player that refuses one may be perfectly happy with the other.

It also explains why changing container is often fast and lossless while changing codec is neither. Moving the same stream into a different box rewrites the box; re-encoding rewrites the picture.

GIMP, Squoosh and ImageMagick read it, and so do most programs of the same kind.

If a file will not open, the format is rarely the problem — it is more often that the program predates it. Converting to something older is the reliable way past that, and it is what the rest of this site is for.

Current browsers read it; older ones do not.

Where support is uneven, serving a second format alongside it is the usual answer — the browser takes the one it understands and nobody is left out.

AVIF can hold EXIF, XMP and ICC profiles.

Whether any of it survives a conversion depends entirely on the target, and the honest answer is usually "some of it".

AVIF is meant to be handed over rather than worked in. Editing one is possible and rarely pleasant; the sane approach is to change the source and export again.

The recurring complaints: it is slow to write compared with its neighbours.

None of these is a reason to avoid the format. They are the things worth knowing before you are surprised by one, which is a different claim and a more useful one.

AVIF stores still images using AV1, the video codec developed by the Alliance for Open Media — Google, Mozilla, Netflix, Amazon, Apple and others — and released in 2018. An AVIF is essentially a single AV1 frame in a container.

It compresses roughly 50 per cent smaller than JPEG at matched visible quality and about 20 per cent smaller than WebP. Several formats have claimed similar numbers before; what makes this one different is that every major browser now decodes it, which no previous challenger achieved.

Technically AVIF and HEIC are close relatives: similar container lineage, similar capabilities, similar compression. The difference is that HEIC uses HEVC, covered by patent pools charging per-device royalties, and AVIF uses AV1, which the alliance built specifically to be royalty-free.

That single difference decided everything. Browsers could ship an AV1 decoder without negotiating licences, and could not do the same for HEVC. It is why the technically comparable formats ended up in completely separate worlds — HEIC on phones and nowhere else, AVIF on the web and increasingly everywhere.

This is the part most writing about AVIF omits. Encoding is expensive — often ten to fifty times slower than JPEG for the same image, and slower than WebP by a wide margin. Decoding is fast, which is the right way round, but the asymmetry is severe.

For a site with a build step that produces images once and serves them millions of times, this is a non-issue and the bandwidth saving is pure gain. For anything converting images on demand, or for a person converting a folder of holiday photographs on a laptop, the wait is real and is the honest reason to weigh WebP instead.

Ten and twelve bits per channel rather than eight, which is what stops a gradient banding. Wide colour gamuts and HDR, so an image can be brighter and more saturated than sRGB allows on a display that supports it. A proper alpha channel, including on lossy images. Lossless mode. Animation.

That last combination — a photographic image with soft transparent edges, lossily compressed — has no equivalent in JPEG or PNG and is genuinely useful. The HDR support is the one most likely to matter in the next few years, as displays capable of showing it become ordinary.

Where AVIF is most impressive is not at high quality settings but at aggressive ones. At file sizes where JPEG produces obvious blocking and WebP produces visible smearing, AVIF still looks reasonable — smooth rather than broken.

The consequence is that the settings people carry over from JPEG are usually wrong. A quality figure that would be reckless in JPEG frequently produces an acceptable AVIF, and pushing harder than instinct suggests is where the format’s advantage actually lives. Judge it by looking rather than by the number.

AVIF at low quality does not break up the way JPEG does — it smooths. Fine texture such as skin pores, fabric weave, foliage detail and film grain can be quietly flattened into something cleaner and less real.

That is often preferable to blocking and it is a different failure mode, which matters if you are checking quality by looking for artefacts. There will not be any obvious ones; there will be less detail than there was. Compare against the original at full size rather than looking for damage.

Every current browser reads AVIF — Chrome since 2020, Firefox 2021, Safari 2022 — and it works in recent Windows, macOS, Android and iOS. That is a much better position than WebP was in at the same age.

Outside that it thins quickly. Desktop photo software is inconsistent, print services and photo labs generally refuse it, older devices do not know it, and a great many upload forms have never heard of it. The pattern is the same one WebP went through: solid in the browser, patchy everywhere else, improving each year.

AVIF where the images are produced once and served many times, where the size saving compounds, and where HDR or ten-bit colour matters. WebP where encoding speed matters, where support outside the browser is a consideration, or where the 20 per cent difference does not justify the added complexity.

Serving both is the arrangement most large sites use, with the browser choosing. For a single person converting a folder of images, WebP is usually the more practical answer and AVIF the more impressive one — which is a distinction worth making rather than blurring.

JPG when the image is a photograph going somewhere that will not accept AVIF — a print service, an older program, a submission form. Expect a considerably larger file at the same visible quality. PNG when the image has transparency or is a screenshot or diagram, where JPG would flatten the alpha and blur the edges.

Bit depth is the one real loss. A ten-bit AVIF converted to an eight-bit JPEG or PNG has fewer levels available in gradients, which can show as banding in a sky. It is rarely visible and it is permanent, so keep the original where the photograph matters.