> libjxl's maximum effort is very slow. It produces files 2–7% smaller than its default for photos, and ~25% smaller for the screenshot and illustration, but takes 9–46 seconds, which is 50–180x as long as its default. jixel gets the same results in a couple of seconds.
libjxl's slow speed at efforts >7 is primarily due to an iterative evaluation-optimization loop of a perceptual error metric called Butteraugli (by tuning quantization weights). This, as well as some other computations in libjxl encoding, happen to be data-parallel and run faster on GPUs than multicore CPUs.
In case anyone is interested, I've been working on a GPU-accelerated libjxl port (supporting CUDA and Metal for now) that makes this much faster, closer to libjxl's normal speeds: https://github.com/yunho-c/gjxl - geared for encoding a large batch images into JPEG XL. It's also faster by around 2.9x at normal effort (7).
AVIF is fantastic format and I use it in my production applications. Spent quite a bit of time looking to the best settings (at least for up to 2k images) and for anyone interested in converting images to AVIF, here's what I've found to work the best for creating the smallest size (10x+ smaller) while still retaining good quality and even supports PNG transparency:
in my app i was using jpeg but then switched to webp two years ago, they're for generating/displaying thumbnails for images and videos. and now avif seems like a better fit? anything that you're not happy about? considering avif now, appreciate any ideas
That F1 image is, in my mind, proof of exactly what is wrong with AVIF. If you look closely the beautiful highlights on the car have been erased and replaced with something plausible. Once you see it you can't unsee it and it boggles my mind that people are still using it as an example.
Granted, AVIF performs impressively for, say, a huge hero image for a blog where you're out to create an overall impression and people aren't going to look at it closely. It does not impress me when I am compressing photos I took with my mirrorless and I expect them to look like photos taken with a mirrorless and not cell phone snaps.
I'm looking as closely as I'm able, and I don't see what you mean. (I'm not a car guy, or a photo guy.) What do you mean by highlights? What am I looking for? Reflections?
Look between the Eni and ApeCoin logos. In lossless you can see there are lines from what I assume separate pieces assembled together. Next to ApeCoin there's also a round piece in the lossless version which is missing from the AVIF. JPEG XL loses most of these as well though.
That's what I noticed anyway, not a car or photo guy either.
If you are referring to "lines from what I assume separate pieces assembled together." I didn't mean that the photo was assembled from multiple pieces, I meant that part of car was (panels or similar). Those lines between panels were no longer visible.
You're looking at it in a browser that doesn't support JPEG XL, so it's falling back to a WASM renderer, and I think it handles resizing differently.
This is totally my bad. I thought I was doing a good thing by adding that fallback renderer, but it isn't identical and it's giving people the wrong impression.
The lossless version is JPEG XL, hence the difference to AVIF.
In Firefox 157.0.1, the right border of the image moves by a pixel or two when I press "hold for lossless" while viewing the AVIF. I think it's the lossy AVIF that's a bit too small.
I think people are really forgetting that JXL's encoders are bad right now. For instance, in TFA Jake presents
- The Firefox screenshot w/ lossless JXL at 66.9kB, when with a better encoder you get get it down to like 40.7kB (39% smaller) [1] (or 43kB if you need it to work with jxl-rs [2])
- The cat illustration w/ lossless JXL at 255.3kB, when with a better encoder you can get it down to 178kB (30% smaller) [3]
Oh, that explains! I tried AVIF and JXL a few years ago and one of the two took ages to encode (a minute versus <1s for jpeg) to get similar compression ratios, and the other was somewhat reasonable on cpu complexity but significantly worse quality at the same size / much bigger to achieve the same quality as good old jpeg. I ended up concluding that jpeg is still the best for the specific image I was trying to lossily compress, but that was probably just the encoder then
Having lived through the MP3 era and experienced the many years/decades? that it took for experts across fields to come together and figure out LAME and the bag of parameters that ultimately made it better than most audio formats around it, I would lean towards waiting this one out, and not take any announcement of a "winner" as gospel. We've yet to see the codecs mature and refine for some time.
I also remember the big claims about WebP's superiority, which ended-up in practice, at equivalent file-size, mostly trading away some of the JPEG artifacts that we all know for some unusual new ones.
I don't think there's a large-enough margin in this space that a new format could chew into to make the general public care: image compression seems like a solved problem overall. The second best thing is to come-up with a format that can make the content producers not have to care either, i.e. be the best in class or close-enough in a variety of use-cases (lossy, lossless, fast, animated, hdr, progressive, …). My naive impression was that jxl is mostly interesting in that regard.
Another interesting niche is in between JPEG and RAW. RAW files are a pain to deal with, but editing JPEGs can be problematic due to bit depth and whatnot. Personally I just want to shoot pictures and not edit/convert/whatever, but sometimes I have a shot that could benefit from a bit of adjustment, and that's where even large JPEGs have an issue. Bit depth and whatever isn't suitable.
I've been using AVIF on my blog for a few years. My blog's image corpus is almost entirely videogame screenshots, and I keep the original PNGs so I can re-encode if better encoders release. Despite playing around with JPEGXL every year or so, AVIF images usually looked better (if only a little) at the same file size (vs JPEGXL).
After reading this article, there's something to point to prove I'm not going crazy.
I'm only casually following JPEG-XL and my impression from previous reading here on HN was that JPEG-XL was the best solution available for a wide variety of usecases, but it looks like numbers dont match that claim?
I think many people disliked Google's control of Chrome blocking JPEG XL rather than it being able to compete on its merits.
JPEG XL also has some big benefits for many use cases like lossless re-encoding and supporting higher resolution. AVIF images have a max size of 8192x4352 last I checked. That's not a problem for web images almost all of the time, but there's certainly uses where you might want more. I think AFIV might be limited to 12bit overall while JPEG XL can do 32bit. Again, is that something many will take advantage of on the web? No, but if it's something you care about it might be really meaningful to you.
Also, if you care about the 90% quality level, JPEG XL often outshines AVIF, but when I'm putting images on the web it's often well below that.
Some of it was bad information. I saw some people saying JPEG XL being way less computationally intensive (even less than WebP) and offering much better compression. Some of it was selective data - do you only test things at 95% quality level and declare a winner?
But I think the big thing is that a lot of people wanted the two formats to succeed or fail based on their merits. I think a lot of people don't like AVIF because it isn't well supported outside of browsers - and there can be a hope that the JPEG name would mean JPEG XL would get the kind of adoption JPEG did.
And it's hard to truly compare formats - or benchmark in general. As the article shows, different JPEG XL encoders offer vastly different performance. And when we're dealing with lossy compression, sometimes it can be a bit of personal preference. At some point, people started enjoying the way that MP3 garbled symbols (the instrument) and that was the sound they expected a symbol to make.
JPEG-XL is not the best solution if you want small low-quality images, to reduce your costs for hosting some Web site. AVIF seems appropriate for that goal.
JPEG-XL seems to be the best solution for storing and distributing high-quality images. For myself, I want high-quality images, so JPEG-XL is what matters, both for new images and for compressing the old archives of JPEG images.
While I have my own Web server, it is for private use and not for commercial purposes, so I have no interest in using AVIF to achieve the smallest image sizes, but at a lower quality than I want.
Most of the comparisons are not about what I would call "high quality" images.
And the article supports what I have said.
Quotation from the article:
> But JPEG XL catches up at very high quality. Around SSIMULACRA2 85, libjxl's default matches AVIF's default, and at maximum efforts, jixel 'extraslow' is ~6% smaller than AVIF s0. jixel 'slow' is 10–13% smaller than AVIF's default from SSIMULACRA2 80 upwards.
For a wide variety of usecases, not for every isolated usecase. Today, AVIF is better for showing people ads^W^W^W web content delivery. This article is titled “JPEG XL vs. AVIF for web use-cases”. The other article recently discussed¹ is subtitled “Investigating JPEG XL's place as a Web image codec” and ends:
> JPEG XL isn't useless; it is genuinely compelling technology for use cases beyond the Web.
AVIF ( or even AV1 itself ) has had massive increase in quality improvements over the past 6 years. JPEG XL was close to release in 2020 and finalised in 2021. A lot of the sentiments hold true back then.
JPEG XL has always been targeting high quality encoding metric first before the lower end low BPP images, which AV1 excels at with or without the last 6 years of improvements.
The current top comments about MP3 and LAME is again about how encoder extract maximum potential. JPEG XL was may be the best in 2021, but has been fighting for survival since then.
There a lot of different images that JPEG XL encode better. Screenshots with text is known to be not something they have optimised for or think it could be good at. Lossless mode may be better. Edit: As one of the other comment here proved my point.
Had all of these, even just a hint of AVIF improvement be told, may be the sentiments would have been a little different. But then again I am not one who would trust the same people who sold me WebP and AOM roadmaps.
But at least AV2 is coming. And JPEG XL is finally in every browser. Hopefully we can all have something even better in the future.
It extracts the already quantized DCT coefficients and related data from the JPEG bitstream and re-encodes them with JPEG XL’s more efficient entropy coding and container,
Think of it as zip compression that is specially designed for JPEG and putting the JPEG data in a different/better container.
JPEG is a lossy format. JPEG -> AVIF adds a second loss operation. JPEG to JPEG-XL is lossless but with a smaller file size. So one does not further degrade the jpegs beyond what they were already degraded in creating them in the first place.
Unfortunately for the comparison-focused blog post the comparison widgets is pretty bad - you can't quickly compare 2 reference pictures (original vs AVIF or original vs JXL) at different scalings like here https://web.archive.org/web/20200915201019/https://afontenot...
(also like the BPP size metric that is picture size-independent)
Wish that widget with improvements (that allows comparison of 3 pics with 3 buttons: original/codec1/codec2) were the widespread standard
(also, "hold" is a rather unergonomic action)
Otherwise, seems like AVIF has had impressive gains in both speed and quality, wonder whether JXL could catch up
>Animated image formats are dumb and animated JPEG XL is no exception. Video formats are better at video. They're built for it. They're optimised for it. Not just in terms of encoding, but also in terms of playback.
This is something I've felt doesn't get enough attention when comparing JXL and AVIF. AVIF can be the replacement for GIF.
><video muted autoplay> is right there.
>No, I'm not adding a demo. I don't want it on my server. Use video formats for video.
I'm not sure if "Use video formats for video" is saying to use AVIF over JXL or saying to use AV1 over AVIF. If the latter, GIF-like animations have a different enough user expectation that it makes sense to have it as something different from regular videos. Even <video muted autoplay> doesn't encode the full expected behavior because GIFs are not expected to have controls like pause, play and scrub. And even if you hide the controls users will expect similar behavior when opening it in an image viewer or in a new tab. Images do not have controls so they fit better as an image, although maybe they need their own category.
Also, I didn't realize how good AVIF was at progressive rendering. I don't think I knew it could do that at all. I think AVIF is the clear winner for the web, although it is still nice to have JXL for lossless. Somehow I feel that AVIF still hasn't gained as much usage as it should, especially now that it is supported almost everywhere. I think I see more webp than AVIF, and JPEG is still everywhere. Maybe now that JXL is out, developers will take another look? AVIF is supported by 96.35%-98.83% of browsers according to caniuse whereas webp is 97.18%-99.68% and JPEG is 97.28%-99.78%.
I also didn't know there was a Rust JXL encoder named jixel.[0]
I agree that animated images make sense as a category. But I wish I did get controls on them when opened directly. Being unable to pause a gif leads to very annoying workarounds sometimes.
JPEG transcoding is one of the neatest features of JXL; there is so much existing jpeg out there. Eventually that may be unnecessary, but it's looking like this could already save a significant amount of space for photo archive backups for example.
> AVIF is basically the keyframe format of AV1 video, with a bunch of still-image-specific optimisations thrown in. Animated AVIF however, is pretty much just a repackaging of AV1 video.
What optimizations are being added? I thought it was basically the exact same codec, but different packaging and usually some adjustment to how the encoder is tuned.
Apologies if your comment was meant to be a parody as there's a bit of Poe's law around this stuff…
IE never supported AVIF. Edge even shipped AVIF later than Chrome. One of the leaders of JPEG XL worked at Google until relatively recently. A massive amount of JPEG XL development has been done by a team at Google.
I don't have any real use cases for jxl or avif or any other modern format b/c I rarely host images but all these articles are always so interesting to me. And at the end of it, I'm left wondering, is there ever going to be a single winner here?
> AVIF is basically the keyframe format of AV1 video, with a bunch of still-image-specific optimisations thrown in. Animated AVIF however, is pretty much just a repackaging of AV1 video. You can convert an AV1 MP4 to AVIF and back losslessly - it's just a container change. That's why it performs so much better, because it's built for motion.
So, is animated AVIF only keyframes / p-frames, where each frame is independent from the other? I was under that impression, uncertain if there are any other capabilities it might have (like only updating part of the canvas when only parts change, like GIF supports)
No. I used to think this too, but it isn't limited to keyframes.You can convert an AV1 MP4 to AVIF and back losslessly - even if it has non-keyframes. It's just a different container. It has the full AV1 capability. Plus transparency.
A little while ago, I chucked together a comparison game on image file formats (incl a stab at av2 images), encoders, parameters to back out preferences relative to ssimulacra2 and butteraugli: https://aadhar.sh/pixel-peeper
It does seem like AVIFs win on small images, and JXL gives you progressive rendering, easy upgradability on JPEGs, and better lossless and high bitrate images.
The question now is how much of AVIF's advantage comes from the encoder compared to the image format itself. If it is the encoder, does JPEG XL even stand a chance of catching up? AVIF will certainly receive further improvements, albeit at a diminishing rate.
For me personally, AVIF is still better, for various
reasons (not solely file size compression ratio as such,
though this is my number one go-to objective; browser
support is also useful but to me is not so important as
it is).
I am keeping a close eye on JPEG-XL, but right now I am
quite settled on .avif. All my local collection is in
.avif, when before it was a mixture of .jpg, .png and
a few animated .gifs. From my findings a few years ago,
avif is superior to jpg, png and gifs on pretty much
everything it matters. On very high compression, though,
I also noticed artefacts, but we had that even more so
with jpg, and for 1:1 comparable file size, avif beats
jpg with both eyes closed.
By the way, great article. I hope he can do another review,
based on that blog entry, in, say 3 years. Would be
interesting to see how avif and jpeg-xl have improved. In
all likelihood I will still keep on using avif, but if
jpeg-xl is a real winner in some areas, I may use it.
(Lossless is one area where jpeg-xl excels, but I don't
need to store satellite data; I want to store old family
pictures in an efficient manner, and here it seems avif
is better.)
JPEG is fast as fuck, due to it being designed for decades old hardware.
When it comes to hardware encoders, the nicest thing you can say about them is they're fast. Software tends to do way better at quality. Hardware AV1 encoders will be tuned for video rather than stills.
Jake's interest in F1 hasn't waned, which is good to see. I am presuming that picture of an Alpine/Renault at Goodwood is his 18Mb photo, but I could be wrong. Neither has his interest im image compression waned, which is also good to see. But why the move from Google to Firefox?
I am still on webp, thinking that I am on the bleeding edge in a world where artworkers are obsessed with pixels with JPG/PNG as the only formats they know, which is an advance on GIF.
Every browser advertises what formats it will accept and if it is in 'data-saving, low bandwidth mode', so I just configure the CDN to keep the names the same '.jpg' but to send the bestest format for the situation/browser, whether that be webp or AVIF, fetching super-high resolution files from the origin server, outputting them in 'retina' resolution with none of those 'picture' elements referencing half a dozen 'responsive' sizes.
In this way nobody has to care what image format is being served, and if it is deemed that everything is way too compressed, the CDN can be flushed of the cached images, quality increased, and cache rebuilt.
It looks like I will need to update my server configuration to use JPEG XL in the usual five years' time, given the lack of any revolutionary benefit.
I was at Google for 10 years, then went to Shopify for 2 years, but I missed the web. For most of the time I was at Google, it mostly did what was good for the web, rather than pushing Google's interests, but that started to change, which is one of things that led to me leaving. E.g. see what happened with the Prompt API.
What good is a really small file size if small but significant fraction of the people who view the page see nothing at all? I loaded this page and I can read the text and see the plots but none of the example images display.
It'd be interesting to scale this up to a lot of images - and have users blind A/B test, like the LLM Arena on Huggingface which helped filter out "benchmaxxing" vs actual intelligence & utility. Because 1) images can be so diverse* and 2) an intrinsic tradeoff might exist between general efficiency and out-of-distribution robustness.
It's hard to rigorously judge a codec from a handful images, especially given the large impact they would have (with a widely adopted codec encoding bazillions of images in the coming years).
* There are many intricate details that go into codecs and visual perception. For instance, our sensitivity to visual errors are dependent on colors (all of hue, saturation, and brightness), spatial frequency of artifacts, local contrast and texture presence, et cetera.
And like OP mentioned, perceptual error metrics (including SSIMULACRA2) aren't perfectly representative of human-evaluated visual quality. For instance, libjxl deliberately makes choices that hurt SSIMU2 scores, but improve human-rated quality.
There was a study done while I was at Google, and I fought for it to be done on high density screens, because that's what most users have. The response was "but people won't be able to see the artifacts" and my head nearly rotated 180 degrees.
But yes, you can see this with jixel, which I'm really impressed by, but it's so tuned to SSIMU2 that it looks really bad to human eyes in some cases compared to libjxl.
But that is correct and why any proper study should first train the participants on the type of artifacts and trade-offs. Like the reference to JXL choices: think its creator mentioned that AVIF might look nicer for faces because it was "smoothing" them but it was a worse representation of the original. So the study participants would need to be conscious of that trade off and be clear in terms of what they're asked to evaluate - whether the result looks nicer or whether it represents the original better.
This is a good food for thought. Semi-related: It reminds me of the fact that smartphone cameras nowadays use ML based filters to make faces prettier before saving in the first place.
Perhaps we can use clever experiment design to address it, like doing a "full-reference" evaluation (e.g., pick most similar two images, out of encoder A, encoder B, and original) rather than strictly A/B.
Maybe the first step to designing better encoders is to build an extremely accurate visuoperceptual error metric. Seems like ML's rapid progress haven't caught onto it just yet.
Haha, that's a great point! On that note - do you have any good pointers on understanding more about how Butteraugli works? I wholeheartedly agree it is a great metric (which aligns well with my subjective assessment much better than MSE or MS-SSIM), but the Guetzli paper (or the Butteraugli GitHub repo) does not explain the theory behind it in detail.
Seems like others were curious too, given the Wikipedia page on Guetzli mentions:
> Butteraugli. ... How the hundreds of parameters that model the properties of the human visual system were derived remains unexplained.
My rough understanding is its multi-scale convolution architecture was inspired by biological visual perception (perhaps how the layers of visual cortex gradually represent higher level features, ish), and involved some sort of empirical parameter tuning based on human evaluations. It'd also be a very nice resource for beginners wanting to learn more about image/video codecs (like me :)
AVIF is a lifesaver for animation with separate transparency layers so the transparency can change position frame by frame. The only other alternative is WebM which has Safari limitations.
But the performance is so bad it isn't worth using. You're better off encoding a double height AV1 and mashing it together with WebGL https://jakearchibald.com/2024/video-with-transparency/. That's how bad the situation is.
Is there an advantage to this as a separate layer compared to just having an alpha channel baked into the image data itself? If not premultiplied then it would not affect the other channels either.
I think one overlooked aspect is that AVIF is container based. Meaning that once sites support, when AV2, AV3 etc. will come out, there won't be a need to go through another very difficult phase of sites adoption - it will still be AVIF just with newer codec inside, and it will be just up to browsers to catch up on newer versions and newer codecs will address technical needs as times goes.
JPEG XL doesn't have that benefit, while sites adoption is arguably a worse issue than browser adoption.
To demonstrate the point even for AVIF itself - it has been in the browsers for a while. Can you use it on common sites? Good luck if you can, even major sites like GitHub and GitLab have issues with it due to some site code depending on hardcoded list of known formats or other similar problems.
The container is useless. Files based on a newer codec won't display anyway.
ISO-BMFF container is bloated and needlessly complicated. AVIF decoders didn't even want to reuse existing MP4 libraries for it due to all the baggage it brings, and implemented their own minimal parsers.
AVIF would have been better off with a simple wrapper similar to RIFF/PNG or extending AV1's own OBU header (which for inexplicable reason gets its data duplicated inside the HEIF container and then implementations are required to verify that both copies agree!)
I hope AVIF will skip AV2. We don't need yet another almost-identical format to migrate to.
> I think one overlooked aspect is that AVIF is container based.
Many other image formats are. AVIF uses HEIC, the same container that HEIF does.
> when AV2, AV3 etc. will come out, there won't be a need to go through another very difficult phase of sites adoption - it will still be AVIF just with newer codec inside, and it will be just up to browsers to catch up on newer versions and newer codecs will address technical needs as times goes.
Fingers crossed, but AV2-based AVIF specs haven't even been finalized, so who knows.
This doesn't make sense to me. There's enough content negotiation out there that AV2 will need a new content-type parameter. Feature detection is important to browsers.
It's not mandatory, and it would work without using it. The whole point is for forward compatibility support effect for sites which are very slow introducing these kind of changes.
My guess: because the OP forgot that to decode AV2/AV3 it matters not that it is in an AVIF container, it matters that the display system (browser, etc.) actually have the codec available to it that can decode the new format (AV2/AV3/etc.).
With no codec for a new compression algorithm, it does not matter if the browser can read the container, you still see the "broken image" icon on your display.
You didn't get the point of the post. I explained why and how container matters here. Not a specific container, but just the idea of container itself. Hint, it's not the browser.
> libjxl's maximum effort is very slow. It produces files 2–7% smaller than its default for photos, and ~25% smaller for the screenshot and illustration, but takes 9–46 seconds, which is 50–180x as long as its default. jixel gets the same results in a couple of seconds.
libjxl's slow speed at efforts >7 is primarily due to an iterative evaluation-optimization loop of a perceptual error metric called Butteraugli (by tuning quantization weights). This, as well as some other computations in libjxl encoding, happen to be data-parallel and run faster on GPUs than multicore CPUs.
In case anyone is interested, I've been working on a GPU-accelerated libjxl port (supporting CUDA and Metal for now) that makes this much faster, closer to libjxl's normal speeds: https://github.com/yunho-c/gjxl - geared for encoding a large batch images into JPEG XL. It's also faster by around 2.9x at normal effort (7).
AVIF is fantastic format and I use it in my production applications. Spent quite a bit of time looking to the best settings (at least for up to 2k images) and for anyone interested in converting images to AVIF, here's what I've found to work the best for creating the smallest size (10x+ smaller) while still retaining good quality and even supports PNG transparency:
in my app i was using jpeg but then switched to webp two years ago, they're for generating/displaying thumbnails for images and videos. and now avif seems like a better fit? anything that you're not happy about? considering avif now, appreciate any ideas
Hmm, I haven't tested this, but I'm deeply sceptical. avifenc is now optimised very well for still images, and you're bypassing all of that here.
These settings have worked very well for me so far, but if you are aware of even better settings, I'd certain like to give it a try.
avifenc. The latest version.
Ah, I actually wasn't aware that "avifenc" was a separate executable. Thanks for the information. I will definitely do some comparison testing.
It's part of libavif. I've usually compiled it myself.
https://github.com/aomediacodec/libavif
avifenc supports args like enable-chroma-deltaq. I've used those but recently stopped, and nothing substantial changed.
That F1 image is, in my mind, proof of exactly what is wrong with AVIF. If you look closely the beautiful highlights on the car have been erased and replaced with something plausible. Once you see it you can't unsee it and it boggles my mind that people are still using it as an example.
Granted, AVIF performs impressively for, say, a huge hero image for a blog where you're out to create an overall impression and people aren't going to look at it closely. It does not impress me when I am compressing photos I took with my mirrorless and I expect them to look like photos taken with a mirrorless and not cell phone snaps.
Would you be able to circle these highlights? I viewed - https://jakearchibald.com/c/original-CXtAofvc.jpg - https://jakearchibald.com/c/avif-q39-e0-d8-yuv444-ssimu70.4-... at 100% magnification at peeped around for a few minutes but didn't notice anything. Maybe my eyes / monitor is bad...
Oh crap, it's this image
https://jakearchibald.com/2020/avif-has-landed/demos/compare...
I was talking about. He linked another one! Guess people finally realized that one sucks and now they have a new one. I screwed up.
They didn't even have the halo back then!
I'm looking as closely as I'm able, and I don't see what you mean. (I'm not a car guy, or a photo guy.) What do you mean by highlights? What am I looking for? Reflections?
Look between the Eni and ApeCoin logos. In lossless you can see there are lines from what I assume separate pieces assembled together. Next to ApeCoin there's also a round piece in the lossless version which is missing from the AVIF. JPEG XL loses most of these as well though.
That's what I noticed anyway, not a car or photo guy either.
The original is a single photo.
If you are referring to "lines from what I assume separate pieces assembled together." I didn't mean that the photo was assembled from multiple pieces, I meant that part of car was (panels or similar). Those lines between panels were no longer visible.
Oh, yeah, haha!
I agree fwiw. The only one that looks bad to me is jixel at lower qualities.
OH WAIT. I KNOW WHAT'S HAPPENING HERE.
You're looking at it in a browser that doesn't support JPEG XL, so it's falling back to a WASM renderer, and I think it handles resizing differently.
This is totally my bad. I thought I was doing a good thing by adding that fallback renderer, but it isn't identical and it's giving people the wrong impression.
The lossless version is JPEG XL, hence the difference to AVIF.
In Firefox 157.0.1, the right border of the image moves by a pixel or two when I press "hold for lossless" while viewing the AVIF. I think it's the lossy AVIF that's a bit too small.
by the way, why not convert everything to png for comparisons to avoid browser support issues?
All browsers support AVIF and JPEG XL now. I was hoping to keep their download size benefits.
Firefox added support only 3 days ago! And this doesn't cover the ESR version.
Sure but this is a technical post aimed at a technical audience.
I think people are really forgetting that JXL's encoders are bad right now. For instance, in TFA Jake presents
- The Firefox screenshot w/ lossless JXL at 66.9kB, when with a better encoder you get get it down to like 40.7kB (39% smaller) [1] (or 43kB if you need it to work with jxl-rs [2])
- The cat illustration w/ lossless JXL at 255.3kB, when with a better encoder you can get it down to 178kB (30% smaller) [3]
[1] https://www.linolevan.com/05-screenshot.jxl
[2] https://www.linolevan.com/05-screenshot-web.jxl
[3] https://www.linolevan.com/06-illustration.jxl
Happy to see your version of the cat illustration doesn't come with massive decoder overhead. Are you planning to open source this encoder?
It's just a side project I'm working on with some friends. May release it if it's interesting to folks.
Oh, that explains! I tried AVIF and JXL a few years ago and one of the two took ages to encode (a minute versus <1s for jpeg) to get similar compression ratios, and the other was somewhat reasonable on cpu complexity but significantly worse quality at the same size / much bigger to achieve the same quality as good old jpeg. I ended up concluding that jpeg is still the best for the specific image I was trying to lossily compress, but that was probably just the encoder then
Thank You. I was about to post I suspect both of those images would have worked better with JXL lossless.
Curious what is the better encoder here referring to?
It's an unreleased one. There's a whole section in the article about lossless, which includes data on those images, but not this mystery unreleased encoder https://jakearchibald.com/2026/jpeg-xl-vs-avif/#lossless
Yeah, it's very cool that jixel was able to achieve such large efficiency improvements!
Having lived through the MP3 era and experienced the many years/decades? that it took for experts across fields to come together and figure out LAME and the bag of parameters that ultimately made it better than most audio formats around it, I would lean towards waiting this one out, and not take any announcement of a "winner" as gospel. We've yet to see the codecs mature and refine for some time.
I also remember the big claims about WebP's superiority, which ended-up in practice, at equivalent file-size, mostly trading away some of the JPEG artifacts that we all know for some unusual new ones.
I don't think there's a large-enough margin in this space that a new format could chew into to make the general public care: image compression seems like a solved problem overall. The second best thing is to come-up with a format that can make the content producers not have to care either, i.e. be the best in class or close-enough in a variety of use-cases (lossy, lossless, fast, animated, hdr, progressive, …). My naive impression was that jxl is mostly interesting in that regard.
> I don't think there's a large-enough margin in this space that a new format could chew into to make the general public care
What improvement do you think is necessary for people to care?
Genuinely curious. Spoiler link with my answer to avoid any bias: https://lgms.nl/p/cau/?b64&ZVRNb9QwEL0j9T%2BMKqFtpe1Cqcq9qoT...
Another interesting niche is in between JPEG and RAW. RAW files are a pain to deal with, but editing JPEGs can be problematic due to bit depth and whatnot. Personally I just want to shoot pictures and not edit/convert/whatever, but sometimes I have a shot that could benefit from a bit of adjustment, and that's where even large JPEGs have an issue. Bit depth and whatever isn't suitable.
I've been using AVIF on my blog for a few years. My blog's image corpus is almost entirely videogame screenshots, and I keep the original PNGs so I can re-encode if better encoders release. Despite playing around with JPEGXL every year or so, AVIF images usually looked better (if only a little) at the same file size (vs JPEGXL).
After reading this article, there's something to point to prove I'm not going crazy.
I'm only casually following JPEG-XL and my impression from previous reading here on HN was that JPEG-XL was the best solution available for a wide variety of usecases, but it looks like numbers dont match that claim?
I think many people disliked Google's control of Chrome blocking JPEG XL rather than it being able to compete on its merits.
JPEG XL also has some big benefits for many use cases like lossless re-encoding and supporting higher resolution. AVIF images have a max size of 8192x4352 last I checked. That's not a problem for web images almost all of the time, but there's certainly uses where you might want more. I think AFIV might be limited to 12bit overall while JPEG XL can do 32bit. Again, is that something many will take advantage of on the web? No, but if it's something you care about it might be really meaningful to you.
Also, if you care about the 90% quality level, JPEG XL often outshines AVIF, but when I'm putting images on the web it's often well below that.
Some of it was bad information. I saw some people saying JPEG XL being way less computationally intensive (even less than WebP) and offering much better compression. Some of it was selective data - do you only test things at 95% quality level and declare a winner?
But I think the big thing is that a lot of people wanted the two formats to succeed or fail based on their merits. I think a lot of people don't like AVIF because it isn't well supported outside of browsers - and there can be a hope that the JPEG name would mean JPEG XL would get the kind of adoption JPEG did.
And it's hard to truly compare formats - or benchmark in general. As the article shows, different JPEG XL encoders offer vastly different performance. And when we're dealing with lossy compression, sometimes it can be a bit of personal preference. At some point, people started enjoying the way that MP3 garbled symbols (the instrument) and that was the sound they expected a symbol to make.
> AVIF images have a max size of 8192x4352
This isn't true btw. The format supports up to 64k x 64k, although browser decoders currently fail beyond 16k x 16k.
Not sure when you'd serve something like that on a web page though.
JPEG-XL is not the best solution if you want small low-quality images, to reduce your costs for hosting some Web site. AVIF seems appropriate for that goal.
JPEG-XL seems to be the best solution for storing and distributing high-quality images. For myself, I want high-quality images, so JPEG-XL is what matters, both for new images and for compressing the old archives of JPEG images.
While I have my own Web server, it is for private use and not for commercial purposes, so I have no interest in using AVIF to achieve the smallest image sizes, but at a lower quality than I want.
Please read the article. All of the comparisons default to "high" quality, according to JXL's own metric.
Most of the comparisons are not about what I would call "high quality" images.
And the article supports what I have said.
Quotation from the article:
> But JPEG XL catches up at very high quality. Around SSIMULACRA2 85, libjxl's default matches AVIF's default, and at maximum efforts, jixel 'extraslow' is ~6% smaller than AVIF s0. jixel 'slow' is 10–13% smaller than AVIF's default from SSIMULACRA2 80 upwards.
I believe that:
ssimulacra2 85 is rather close to median quality in the internet
ssimulacra2 90-95 is rather close to high quality in the internet
ssimulacra2 98+ is close to camera quality
> for a wide variety of usecases
For a wide variety of usecases, not for every isolated usecase. Today, AVIF is better for showing people ads^W^W^W web content delivery. This article is titled “JPEG XL vs. AVIF for web use-cases”. The other article recently discussed¹ is subtitled “Investigating JPEG XL's place as a Web image codec” and ends:
> JPEG XL isn't useless; it is genuinely compelling technology for use cases beyond the Web.
¹ https://news.ycombinator.com/item?id=49690554
(Either way, can we agree to take webp out behind the barn?)
AVIF ( or even AV1 itself ) has had massive increase in quality improvements over the past 6 years. JPEG XL was close to release in 2020 and finalised in 2021. A lot of the sentiments hold true back then.
JPEG XL has always been targeting high quality encoding metric first before the lower end low BPP images, which AV1 excels at with or without the last 6 years of improvements.
The current top comments about MP3 and LAME is again about how encoder extract maximum potential. JPEG XL was may be the best in 2021, but has been fighting for survival since then.
There a lot of different images that JPEG XL encode better. Screenshots with text is known to be not something they have optimised for or think it could be good at. Lossless mode may be better. Edit: As one of the other comment here proved my point.
Had all of these, even just a hint of AVIF improvement be told, may be the sentiments would have been a little different. But then again I am not one who would trust the same people who sold me WebP and AOM roadmaps.
But at least AV2 is coming. And JPEG XL is finally in every browser. Hopefully we can all have something even better in the future.
JPEG-XL can be a quick win since it is possible to do a transcode of all of your existing ('classic') JPEG files with zero (visual) losses in quality.
I always think of transcode and lossless as opposites. How is this achieved in this format?
It extracts the already quantized DCT coefficients and related data from the JPEG bitstream and re-encodes them with JPEG XL’s more efficient entropy coding and container,
Think of it as zip compression that is specially designed for JPEG and putting the JPEG data in a different/better container.
If you're transcoding why wont you go to avif or another one? If jpeg -> jpeg-xl uniquely better?
JPEG is a lossy format. JPEG -> AVIF adds a second loss operation. JPEG to JPEG-XL is lossless but with a smaller file size. So one does not further degrade the jpegs beyond what they were already degraded in creating them in the first place.
Claims around JPEG XL have always been wild. E.g. this from one of the creators https://x.com/jyzg/status/1592811472073416704
That's.. horrific. How can someone be this out of touch?
Unfortunately for the comparison-focused blog post the comparison widgets is pretty bad - you can't quickly compare 2 reference pictures (original vs AVIF or original vs JXL) at different scalings like here https://web.archive.org/web/20200915201019/https://afontenot...
(also like the BPP size metric that is picture size-independent)
Wish that widget with improvements (that allows comparison of 3 pics with 3 buttons: original/codec1/codec2) were the widespread standard (also, "hold" is a rather unergonomic action)
Otherwise, seems like AVIF has had impressive gains in both speed and quality, wonder whether JXL could catch up
For a moment I was sad the original comparison page was gone. It turns out it is still online under the developer's new GitHub username: https://lmfont.github.io/image-formats-comparison/#abandoned....
Thanks! Was also sad, but it's "just" linkrot, will update bookmarks
Offering different scalings is pointless because they're designed for a single largest size.
But they won't be viewed at different sizes? But even then, the point is in making detection of artifacts easier
>Animated image formats are dumb and animated JPEG XL is no exception. Video formats are better at video. They're built for it. They're optimised for it. Not just in terms of encoding, but also in terms of playback.
This is something I've felt doesn't get enough attention when comparing JXL and AVIF. AVIF can be the replacement for GIF.
><video muted autoplay> is right there.
>No, I'm not adding a demo. I don't want it on my server. Use video formats for video.
I'm not sure if "Use video formats for video" is saying to use AVIF over JXL or saying to use AV1 over AVIF. If the latter, GIF-like animations have a different enough user expectation that it makes sense to have it as something different from regular videos. Even <video muted autoplay> doesn't encode the full expected behavior because GIFs are not expected to have controls like pause, play and scrub. And even if you hide the controls users will expect similar behavior when opening it in an image viewer or in a new tab. Images do not have controls so they fit better as an image, although maybe they need their own category.
Also, I didn't realize how good AVIF was at progressive rendering. I don't think I knew it could do that at all. I think AVIF is the clear winner for the web, although it is still nice to have JXL for lossless. Somehow I feel that AVIF still hasn't gained as much usage as it should, especially now that it is supported almost everywhere. I think I see more webp than AVIF, and JPEG is still everywhere. Maybe now that JXL is out, developers will take another look? AVIF is supported by 96.35%-98.83% of browsers according to caniuse whereas webp is 97.18%-99.68% and JPEG is 97.28%-99.78%.
I also didn't know there was a Rust JXL encoder named jixel.[0]
[0] https://github.com/awxkee/jixel
I agree that animated images make sense as a category. But I wish I did get controls on them when opened directly. Being unable to pause a gif leads to very annoying workarounds sometimes.
nit: another rust ENCoder, not DE
Though given the lagging speed in decoding, is there a faster tying JXL decoder planned?
jxl-rs is rust (used in Firefox and Chrome), and already faster than libjxl (used in Safari).
Fixed that, thanks!
JPEG transcoding is one of the neatest features of JXL; there is so much existing jpeg out there. Eventually that may be unnecessary, but it's looking like this could already save a significant amount of space for photo archive backups for example.
That's just by changing the entropy coder and retaining the DCT coefficients. The idea is similar to Dropbox's Lepton. https://dropbox.tech/infrastructure/lepton-image-compression...
The main difference being that Lepton is worse and 100x slower.
Lepton guarantees that JPEG->Lepton->JPEG produces an identical file, not just identical pixels. Does JPEG XL achieve the same thing?
Great article!
Overall I am getting that AVIF is better on the web...unless Lossless is needed, in that case better take JPEGXL.
> AVIF is basically the keyframe format of AV1 video, with a bunch of still-image-specific optimisations thrown in. Animated AVIF however, is pretty much just a repackaging of AV1 video.
What optimizations are being added? I thought it was basically the exact same codec, but different packaging and usually some adjustment to how the encoder is tuned.
tune=iq is the main bit https://aomedia.org/blog%20posts/Libavif_v1_4_0-Boasts-Major...
Perhaps useful:
* https://caniuse.com/?search=avif
* https://caniuse.com/?search=jpegxl
Note about caniuse: browsers dragged their feet with jpegxl while avif had the backing of the biggest browser in existence: internet explorer
Apologies if your comment was meant to be a parody as there's a bit of Poe's law around this stuff…
IE never supported AVIF. Edge even shipped AVIF later than Chrome. One of the leaders of JPEG XL worked at Google until relatively recently. A massive amount of JPEG XL development has been done by a team at Google.
I don't have any real use cases for jxl or avif or any other modern format b/c I rarely host images but all these articles are always so interesting to me. And at the end of it, I'm left wondering, is there ever going to be a single winner here?
> AVIF is basically the keyframe format of AV1 video, with a bunch of still-image-specific optimisations thrown in. Animated AVIF however, is pretty much just a repackaging of AV1 video. You can convert an AV1 MP4 to AVIF and back losslessly - it's just a container change. That's why it performs so much better, because it's built for motion.
So, is animated AVIF only keyframes / p-frames, where each frame is independent from the other? I was under that impression, uncertain if there are any other capabilities it might have (like only updating part of the canvas when only parts change, like GIF supports)
No. I used to think this too, but it isn't limited to keyframes.You can convert an AV1 MP4 to AVIF and back losslessly - even if it has non-keyframes. It's just a different container. It has the full AV1 capability. Plus transparency.
A little while ago, I chucked together a comparison game on image file formats (incl a stab at av2 images), encoders, parameters to back out preferences relative to ssimulacra2 and butteraugli: https://aadhar.sh/pixel-peeper
It does seem like AVIFs win on small images, and JXL gives you progressive rendering, easy upgradability on JPEGs, and better lossless and high bitrate images.
The question now is how much of AVIF's advantage comes from the encoder compared to the image format itself. If it is the encoder, does JPEG XL even stand a chance of catching up? AVIF will certainly receive further improvements, albeit at a diminishing rate.
https://giannirosato.com/blog/post/case-against-jxl/ suggests JXL is fundamentally limited. We'll see. There's a race on and it's great!
Some days ago we had a similar discussion here.
For me personally, AVIF is still better, for various reasons (not solely file size compression ratio as such, though this is my number one go-to objective; browser support is also useful but to me is not so important as it is).
I am keeping a close eye on JPEG-XL, but right now I am quite settled on .avif. All my local collection is in .avif, when before it was a mixture of .jpg, .png and a few animated .gifs. From my findings a few years ago, avif is superior to jpg, png and gifs on pretty much everything it matters. On very high compression, though, I also noticed artefacts, but we had that even more so with jpg, and for 1:1 comparable file size, avif beats jpg with both eyes closed.
By the way, great article. I hope he can do another review, based on that blog entry, in, say 3 years. Would be interesting to see how avif and jpeg-xl have improved. In all likelihood I will still keep on using avif, but if jpeg-xl is a real winner in some areas, I may use it. (Lossless is one area where jpeg-xl excels, but I don't need to store satellite data; I want to store old family pictures in an efficient manner, and here it seems avif is better.)
1. How long does size, encode time and resize take compared to good old jpeg?
2. Is it possible to encode AVIF with hardware acceleration?
JPEG is fast as fuck, due to it being designed for decades old hardware.
When it comes to hardware encoders, the nicest thing you can say about them is they're fast. Software tends to do way better at quality. Hardware AV1 encoders will be tuned for video rather than stills.
I really hope that some day Firefox supports HDR AVIF images
It's not AVIF that's the issue, the blocker is supporting HDR in general.
Fair point. HDR images in Firefox just do not work at all, regardless of the format.
Jake's interest in F1 hasn't waned, which is good to see. I am presuming that picture of an Alpine/Renault at Goodwood is his 18Mb photo, but I could be wrong. Neither has his interest im image compression waned, which is also good to see. But why the move from Google to Firefox?
I am still on webp, thinking that I am on the bleeding edge in a world where artworkers are obsessed with pixels with JPG/PNG as the only formats they know, which is an advance on GIF.
Every browser advertises what formats it will accept and if it is in 'data-saving, low bandwidth mode', so I just configure the CDN to keep the names the same '.jpg' but to send the bestest format for the situation/browser, whether that be webp or AVIF, fetching super-high resolution files from the origin server, outputting them in 'retina' resolution with none of those 'picture' elements referencing half a dozen 'responsive' sizes.
In this way nobody has to care what image format is being served, and if it is deemed that everything is way too compressed, the CDN can be flushed of the cached images, quality increased, and cache rebuilt.
It looks like I will need to update my server configuration to use JPEG XL in the usual five years' time, given the lack of any revolutionary benefit.
Yep, Alpine, and yep, Goodwood! Nicely done!
I was at Google for 10 years, then went to Shopify for 2 years, but I missed the web. For most of the time I was at Google, it mostly did what was good for the web, rather than pushing Google's interests, but that started to change, which is one of things that led to me leaving. E.g. see what happened with the Prompt API.
Ah, Chrome ships JXL when we already have a better codec for the web!
PDF standardized on JPEG XL, and Chrome ships with a PDF renderer.
What good is a really small file size if small but significant fraction of the people who view the page see nothing at all? I loaded this page and I can read the text and see the plots but none of the example images display.
It'd be interesting to scale this up to a lot of images - and have users blind A/B test, like the LLM Arena on Huggingface which helped filter out "benchmaxxing" vs actual intelligence & utility. Because 1) images can be so diverse* and 2) an intrinsic tradeoff might exist between general efficiency and out-of-distribution robustness.
It's hard to rigorously judge a codec from a handful images, especially given the large impact they would have (with a widely adopted codec encoding bazillions of images in the coming years).
* There are many intricate details that go into codecs and visual perception. For instance, our sensitivity to visual errors are dependent on colors (all of hue, saturation, and brightness), spatial frequency of artifacts, local contrast and texture presence, et cetera.
And like OP mentioned, perceptual error metrics (including SSIMULACRA2) aren't perfectly representative of human-evaluated visual quality. For instance, libjxl deliberately makes choices that hurt SSIMU2 scores, but improve human-rated quality.
There was a large scale study a while back: https://cloudinary.com/blog/contemplating-codec-comparisons
That was done before AVIF had any improvements. Arguably one could even say JPEG XL competition brought the best of AVIF out.
There was a study done while I was at Google, and I fought for it to be done on high density screens, because that's what most users have. The response was "but people won't be able to see the artifacts" and my head nearly rotated 180 degrees.
But yes, you can see this with jixel, which I'm really impressed by, but it's so tuned to SSIMU2 that it looks really bad to human eyes in some cases compared to libjxl.
> but people won't be able to see the artifacts
But that is correct and why any proper study should first train the participants on the type of artifacts and trade-offs. Like the reference to JXL choices: think its creator mentioned that AVIF might look nicer for faces because it was "smoothing" them but it was a worse representation of the original. So the study participants would need to be conscious of that trade off and be clear in terms of what they're asked to evaluate - whether the result looks nicer or whether it represents the original better.
This is a good food for thought. Semi-related: It reminds me of the fact that smartphone cameras nowadays use ML based filters to make faces prettier before saving in the first place.
Perhaps we can use clever experiment design to address it, like doing a "full-reference" evaluation (e.g., pick most similar two images, out of encoder A, encoder B, and original) rather than strictly A/B.
Its creator (me) mentioned the smoothing as a negative.
I feel that!
Maybe the first step to designing better encoders is to build an extremely accurate visuoperceptual error metric. Seems like ML's rapid progress haven't caught onto it just yet.
This was indeed what the JPEG XL effort started with :) The Butteraugli metric.
Haha, that's a great point! On that note - do you have any good pointers on understanding more about how Butteraugli works? I wholeheartedly agree it is a great metric (which aligns well with my subjective assessment much better than MSE or MS-SSIM), but the Guetzli paper (or the Butteraugli GitHub repo) does not explain the theory behind it in detail.
Seems like others were curious too, given the Wikipedia page on Guetzli mentions:
> Butteraugli. ... How the hundreds of parameters that model the properties of the human visual system were derived remains unexplained.
My rough understanding is its multi-scale convolution architecture was inspired by biological visual perception (perhaps how the layers of visual cortex gradually represent higher level features, ish), and involved some sort of empirical parameter tuning based on human evaluations. It'd also be a very nice resource for beginners wanting to learn more about image/video codecs (like me :)
To be honest it's starting to sound like Google were right and adding JPEG XL support was a mistake.
AVIF is a lifesaver for animation with separate transparency layers so the transparency can change position frame by frame. The only other alternative is WebM which has Safari limitations.
But the performance is so bad it isn't worth using. You're better off encoding a double height AV1 and mashing it together with WebGL https://jakearchibald.com/2024/video-with-transparency/. That's how bad the situation is.
Is there an advantage to this as a separate layer compared to just having an alpha channel baked into the image data itself? If not premultiplied then it would not affect the other channels either.
Most of these images are not at 100%. Use large images and show 100% crops everywhere.
You're mistaking CSS pixels for device pixels https://jakearchibald.com/2021/serving-sharp-images-to-high-...
nop
I think one overlooked aspect is that AVIF is container based. Meaning that once sites support, when AV2, AV3 etc. will come out, there won't be a need to go through another very difficult phase of sites adoption - it will still be AVIF just with newer codec inside, and it will be just up to browsers to catch up on newer versions and newer codecs will address technical needs as times goes.
JPEG XL doesn't have that benefit, while sites adoption is arguably a worse issue than browser adoption.
To demonstrate the point even for AVIF itself - it has been in the browsers for a while. Can you use it on common sites? Good luck if you can, even major sites like GitHub and GitLab have issues with it due to some site code depending on hardcoded list of known formats or other similar problems.
The container is useless. Files based on a newer codec won't display anyway.
ISO-BMFF container is bloated and needlessly complicated. AVIF decoders didn't even want to reuse existing MP4 libraries for it due to all the baggage it brings, and implemented their own minimal parsers.
AVIF would have been better off with a simple wrapper similar to RIFF/PNG or extending AV1's own OBU header (which for inexplicable reason gets its data duplicated inside the HEIF container and then implementations are required to verify that both copies agree!)
I hope AVIF will skip AV2. We don't need yet another almost-identical format to migrate to.
> I think one overlooked aspect is that AVIF is container based.
Many other image formats are. AVIF uses HEIC, the same container that HEIF does.
> when AV2, AV3 etc. will come out, there won't be a need to go through another very difficult phase of sites adoption - it will still be AVIF just with newer codec inside, and it will be just up to browsers to catch up on newer versions and newer codecs will address technical needs as times goes.
Fingers crossed, but AV2-based AVIF specs haven't even been finalized, so who knows.
https://github.com/AOMediaCodec/av2-isobmff
This doesn't make sense to me. There's enough content negotiation out there that AV2 will need a new content-type parameter. Feature detection is important to browsers.
I don't think so. WebM doesn't need new content type and it can ship AV1 and VP9 all the same.
What are you talking about? Video formats have a whole mad type parameter for this stuff https://jakearchibald.com/2022/html-codecs-parameter-for-av1...
It's not mandatory, and it would work without using it. The whole point is for forward compatibility support effect for sites which are very slow introducing these kind of changes.
Can someone please explain the downvotes?
My guess: because the OP forgot that to decode AV2/AV3 it matters not that it is in an AVIF container, it matters that the display system (browser, etc.) actually have the codec available to it that can decode the new format (AV2/AV3/etc.).
With no codec for a new compression algorithm, it does not matter if the browser can read the container, you still see the "broken image" icon on your display.
You didn't get the point of the post. I explained why and how container matters here. Not a specific container, but just the idea of container itself. Hint, it's not the browser.
I don't get it. And to me it wasn't clear in the post. As others have explained the container and codec are two separate issues.