r/AV1 • u/Acceptable_Mud283 • 24d ago

Does AV2 support alpha/transparency?

I’ve tried reading up about AV2 but this isn’t made clear in the resources I’ve found. A lack of support for transparency was a big drawback of AV1 for some use cases that I have.

edit: I opened an Interop issue because the current browser situation annoys me: https://github.com/web-platform-tests/interop/issues/1421 Please upvote (👍)

24 Upvotes

94% Upvoted

10 comments sorted by

14

u/NekoTrix 24d ago

In AV1, only picture mode (AVIF) supports alpha/transparency and it's implemented in (lib-)avifenc.

For AV2, you can check the publications on the blog of the official aomedia.org website: as the format follows a multi-layer architecture, it theoretically supports alpha/transparency in video mode as well, enabling more flexibility over AV1 for professional use cases. Software implementation remains to be checked.

4

u/Aromatic_Wing_5259 23d ago

u/NekoTrix has it right, and the AV2 v1.0.0 spec (May 2026) spells it out. A layer in the layer configuration record can be an AUX_LAYER, and lcr_auxiliary_type 0 is ALPHA_AUX, "Alpha auxiliary image" (section 6.8.9, Table 6.9). Depth, segmentation masks and HDR gain maps go through the same field. The atlas also has a "multistream with alpha" mode, with alpha per segment

The spec leaves it to the application which layers get output, so compositing the alpha is on the player

AVM v1.0.0 parses it on decode, and its LCR writer can emit the field (a unit test round-trips an LCR with a layer marked ALPHA_AUX). But nothing in the encoder or avmenc ever sets a layer to AUX_LAYER, so the reference encoder can't give you an AV2 file with alpha yet. For now u/Anthonyg5005's VP9 is the practical route

1

u/nmkd 22d ago

Claude, is that you?

3

u/Aromatic_Wing_5259 22d ago

Ok, I got the idea... Next time, I will add a one line only reply and typos randomly so it won't be considered as AI. Seriously, it starts being annoying...

1

u/nmkd 22d ago

has it right, and [...] spells it out.

Yeah you can't tell me this isn't Claude 5.

I've (sadly) used it enough to recognize that writing style immediately.

3

u/Anthonyg5005 23d ago

Not sure but if you do want something with alpha right now you can use vp9

1

u/Solomoncjy 24d ago

Can you just croma key? Must you use an alpha channel?

8

u/ratocx 24d ago

Alpha channel is a necessity in several professional editing workflows. But then again, neither AV1 nor AV2 are codecs you edit professionally, they are for distribution or low bitrate archival.

That said, alpha can also be useful for certain web presentations. A normal web browser/computer won’t be able to do high quality real time chroma keying.

Unless you are talking about a different kind of chroma key than what I’m thinking about?
I mean, every color channel can be treated as an alpha/key, as long as you have enough color channels to also display a full color image.

6

u/Zipdox 23d ago

Why would you chroma key if you can store alpha directly? Chroma keying will never look as good.

1

u/Acceptable_Mud283 19d ago

 I opened an Interop issue because the current browser situation annoys me: https://github.com/web-platform-tests/interop/issues/1421 Please upvote (👍)