Convert images to AVIF in bulk (CLI)

AVIF is usually the smallest of the modern web image formats — often 20–30% below WebP at comparable quality — and it keeps an alpha channel, so it’s a strong choice for transparent PNGs like logos and icons. The trade-off is encode time: AVIF is slower to produce than WebP. This guide converts a whole folder to .avif in one command, locally, with no upload.

Everything runs against @assetopt/cli (open source, MIT). The number at the end comes from the downloadable sample pack — a real file, not a cherry-picked benchmark. If you only care about WebP, see the companion guide, Convert JPG & PNG to WebP in bulk.

Install

npm install -g @assetopt/cli

Or run it without installing:

npx @assetopt/cli --help

Convert a folder to AVIF

By default the CLI recompresses images in their original format. To target AVIF, add a .assetoptrc that routes your source formats to avif:

{
  "images": {
    "formatMatrix": { "jpeg": "avif", "png": "avif" },
    "quality": { "avif": 55 }
  },
  "output": { "dir": "./optimized" }
}

Then run:

assetopt optimize ./images

Every .jpg and .png under ./images is written as .avif into ./optimized. Originals are left untouched.

To push every image (including existing WebP) to AVIF, use { "images": { "outputFormat": "avif" } } instead of a per-format matrix. See the config reference for the difference.

Preview the savings first

Run a dry run before writing anything — analyze reports exact before/after sizes without touching disk:

assetopt analyze ./images

Swap analyze for optimize once the numbers look right.

Pick a quality that fits

AVIF quality is a 1–100 dial (default 75). AVIF holds up well at lower numbers than JPEG, so 50–60 is often a good starting point for photos:

{ "images": { "formatMatrix": { "jpeg": "avif", "png": "avif" }, "quality": { "avif": 50 } } }

Because AVIF encoding is CPU-heavy, the incremental cache matters here: after the first run, only changed files are re-encoded, so re-running is fast.

The max-compression preset

If your goal is simply the smallest possible payload, the built-in max-compression preset converges every format to AVIF at quality.avif: 50, strips metadata, and fully optimizes SVG:

{ "preset": "max-compression" }

See the preset reference for exactly what each one does.

Real number

On the sample pack, a transparent logo PNG smart-routed to AVIF:

AVIF kept the alpha channel while cutting the file to a sixth of its size — the case where AVIF clearly beats WebP. You can reproduce this with the downloadable pack.

WebP or AVIF?

• AVIF: smallest files, keeps transparency, slower to encode. Best for logos/icons with alpha and for photos where build time isn’t critical.
• WebP: still much smaller than JPEG/PNG, far faster to encode, universally supported. A safe default for large photo batches.

You don’t have to choose globally. assetopt can route by content — transparent → AVIF, opaque → WebP — automatically. That’s what the web-perf preset does; see Smart format conversion.

Next steps

• Convert JPG & PNG to WebP in bulk — the faster-encoding sibling
• CLI reference — every command, flag, and exit code
• Configuration reference — all .assetoptrc fields