Comment by juliobbv | Hacker News Reader

Comment by juliobbv | Hacker News Reader

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> I find it misleading to call AVIF's "up to four passes" "very flexible".

Wow, what a way to misquote me. Let me repeat what I actually said:

> Progressive AVIF is very flexible: it supports up to four passes, at configurable quality and dimension scaling levels. You can have any given pass reference up to two previous ones for refinement (thanks to AV1's strong inter-encoding capabilities), and you add filters to non-final passes (like blurring) to achieve a desired loading aesthetic.

So, I re-iterate progressive AVIF is flexible, because:

- Intermediate passes in AVIF can look as sharp or blurry as desired -- you don't have that kind of control with JXL

- Intermediate passes in AVIF can semantically be different from the final pass -- very useful if you want to add a "loading" mark to the non-final passes to inform the user the image is still loading

- The four pass limit is A GOOD THING, as you want an image format to have a reasonable worst-case upper bound on energy consumption due to sum of partial decoding + display refresh updates -- there's such a thing as having "too many passes", and uncapping the limit would be irresponsible

- You can absolutely do saliency encoding in AVIF, as AV1's inter-frame encoding naturally allows for it efficiently

Ah, an accusation of misquoting. I actually quoted your exact words minus "is" and "it supports".

I think we disagree on the degree of flexibility, for sure.

A cap on layers (under user/browser) absolutely makes sense, but 4 at the format level is quite limiting, especially if you want to spend some of them on salient regions.

I agree that's possible, but not that it's efficient. You'd waste a few KiB on encoding skip blocks - AVIF layers represent the whole image, whereas JPEG XL can efficiently encode and update at group level.

How flexible did Jake find AVIF progressive in 2025? [1]

"it seems pretty limited. Only particular scaling values are allowed, and 1/8 is the smallest. Supposedly, additional layers are possible[..], but whenever I tried this, the encoder would error out, or explode the file size to ~400 kB, even at lowest quality. I guess that's why it's marked 'experimental'."

> Intermediate passes in AVIF can semantically be different from the final pass

Also true of JPEG XL - scans are additive.

[1]: https://jakearchibald.com/2025/present-and-future-of-progres...

I'm not sure if you're aware of this or not but juliobbv is the developer that fixed progressive AVIF, he is fully aware of how it works and how AV1 works in general.

"You'd waste a few KiB on encoding skip blocks" This tells me you don't know how codecs work... skip blocks are not expensive to code, they are very cheap.

Jake's blog post is outdated by the way, the progressive functionality is much more advanced than it was at that point in time because Julio worked on it.

> This tells me you don't know how codecs work

Laughable.

My conservative estimate is that a few-MP image with all but a smallish region encoded using skip blocks will spend a few KiB on that. This is very expensive compared to sending only a bounding box, hence it is unattractive for purposes of updating small regions with a whole-image layer.

I am glad to hear AVIF progressive has improved. But note that my original comment was: I find it misleading to call AVIF's "up to four passes" "very flexible". I believe that stands: contrasting the flexibility of (purpose-built) JPEG XL vs. the fairly strict limitations (inherited from video) of AVIF, I am astonished anyone would still call the latter "very flexible" by comparison.

Hi, I'm the author of the article you're quoting. AVIF was limited at the time of writing, but has since seen massive improvements, including progressive support.

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