Why this pairing exists
If iPhone photos are going onto a website, this is the shortest honest route.
HEIC and AVIF are technical siblings — both are still images built on a video codec, in the same container family. HEIC uses HEVC; AVIF uses AV1. What separates them is licensing rather than engineering: AV1 was designed to be royalty-free, which is why every browser can create AVIF and none can create HEIC.
Converting HEIC to AVIF therefore keeps you in the same family of compression while moving to a format the web can actually display.
Go directly, not via JPG
The tempting route is HEIC to JPG and then JPG to AVIF, because those are the conversions people already know about.
Avoid it. Each lossy step discards a little more detail, and the second encoder then spends bits faithfully reproducing the first one’s artefacts. One step gives a cleaner file, usually at a smaller size.
Expect a slow conversion and a modest saving
This is the slowest pairing on the site: an HEVC decode followed by an AV1 encode, both genuinely expensive.
The size result is usually undramatic. HEIC and AVIF are both modern and both efficient, so the file often lands close to where it started. That is expected — you are converting because browsers render AVIF and do not render HEIC, not to save space.
Where the saving shows up is against the alternative. Converting to JPG instead would produce a considerably larger file for the same web page.
When to pick something else
- Sending the photo to a person → JPG. You cannot predict their software, and AVIF support outside browsers is still thin.
- A website that must support older devices → WebP. Slightly larger, slightly safer.
- Editing the photo → PNG, for a lossless working copy.
The full trade-off between the two modern formats: WebP vs AVIF.