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I have a couple of questions unrelated to this commit:

1. Is there any interest in adding support for libaom (AV1 / AVIF encoding?)
2. libvpx uses --target=generic-gnu was there an issue building the x86 optimizations for

@jzern Thanks for the contribution, but after testing I found that there is no problem to upgrade libvpx to 1.13.1, but upgrading libwebp to 1.2.0+ results in the error below:

Thus, I think libwebp 1.2.1+ is not compatible with ffmpeg n5.1.3 / n5.1.4.

May I trouble you to update this PR to upgrade libvpx to 1.13.1 and libwebp to 1.2.0? Thanks.

Thanks for the contribution, but after testing I found that there is no problem to upgrade libvpx to 1.13.1, but upgrading libwebp to 1.2.0+ results in the error below:

WebPAnimEncoder* come from libwebpmux; see ffmpeg's configure check 1. The motivation behind this change is to ensure the snapshot has all available bug and security fixes. An option is to update to a commit on the 1.2.0 release branch, but I'd prefer is this can get fixed so this code base has the latest code.

How can I reproduce the issue?

I see the issue using make dev. Maybe there was an issue in the ffmpeg snapshot you are using. v1.2.0-8-g20ceff7e is a fallback on the 1.2.0 branch.

@jeromewu this should be fixed now.
I didn't notice in my original change that the libs are explicitly named in Dockerfile and passed ffmpeg-wasm.sh.

Thanks for your contribution!