[BUG] Mastodon won't load .avif images of posts

[3000Neo]

Is there an existing issue for this?

• I have searched the existing issues

Current Behavior

When viewing a post with .avif pictures the pictures don't load.
When setting RAILS_LOG_LEVEL=debug the following error is visible in the docker log:
D, [2025-10-20T18:53:44.055743 #400] DEBUG -- : [03805363-5b8f-4f5c-b715-acd027bd9679] Error fetching remote file: Error while optimizing 0b46c1d2ba8b23e88126430f6a9dd40820251020-400-p9cfns: VipsForeignLoad: "/tmp/0b46c1d2ba8b23e88126430f6a9dd40820251020-400-p9cfns.avif" is not a known file format

Expected Behavior

The pictures of the post get shown

Steps To Reproduce

1. Open a post with .avif images (for example: https://icy.arcticfluff.eu/@toomanyfoxes/statuses/01K7XS068T38TVNV29C9Q8G565 (not my post, just a post where I noticed the problem on my server))
2. Pictures don't load

Environment

- OS: unraid 6.12.10
- How docker service was installed: preinstalled with OS

CPU architecture

x86-64

Docker creation

docker run
  -d
  --name='mastodon'
  --net='bond0'
  --ip='192.168.178.5'
  -e TZ="Europe/Berlin"
  -e HOST_OS="Unraid"
  -e HOST_HOSTNAME="EDIv2"
  -e HOST_CONTAINERNAME="mastodon"
  -e 'TCP_PORT_80'='80'
  -e 'TCP_PORT_443'='443'
  -e 'LOCAL_DOMAIN'=<secret>
  -e 'REDIS_HOST'='192.168.178.19'
  -e 'REDIS_PORT'='6379'
  -e 'DB_HOST'='192.168.178.6'
  -e 'DB_USER'='mastodon'
  -e 'DB_NAME'='mastodon'
  -e 'DB_PASS'=<secret>
  -e 'DB_PORT'='5432'
  -e 'ES_ENABLED'='true'
  -e 'SECRET_KEY_BASE'=<secret>
  -e 'OTP_SECRET'=<secret>
  -e 'VAPID_PRIVATE_KEY'=<secret>
  -e 'VAPID_PUBLIC_KEY'=<secret>
  -e 'SMTP_SERVER'=<secret>
  -e 'SMTP_PORT'='587'
  -e 'SMTP_LOGIN'=<secret>
  -e 'SMTP_PASSWORD'=<secret>
  -e 'SMTP_FROM_ADDRESS'=<secret>
  -e 'S3_ENABLED'='false'
  -e 'WEB_DOMAIN'=<secret>
  -e 'ES_HOST'='192.168.178.216'
  -e 'ES_PORT'='9200'
  -e 'ES_USER'='elastic'
  -e 'ES_PASS'=<secret>
  -e 'S3_BUCKET'=''
  -e 'AWS_ACCESS_KEY_ID'=''
  -e 'AWS_SECRET_ACCESS_KEY'=''
  -e 'S3_ALIAS_HOST'=''
  -e 'TRUSTED_PROXY_IP'='192.168.178.11,127.0.0.1'
  -e 'SINGLE_USER_MODE'='true'
  -e 'ES_PRESET'='single_node_cluster'
  -e 'ACTIVE_RECORD_ENCRYPTION_DETERMINISTIC_KEY'=<secret>
  -e 'ACTIVE_RECORD_ENCRYPTION_KEY_DERIVATION_SALT'=<secret>
  -e 'ACTIVE_RECORD_ENCRYPTION_PRIMARY_KEY'=<secret>
  -e 'LOG_LEVEL'='info'
  -e 'RAILS_LOG_LEVEL'='info'
  -e 'PUID'='99'
  -e 'PGID'='100'
  -e 'UMASK'='022'
  -l net.unraid.docker.managed=dockerman
  -l net.unraid.docker.icon='https://raw.githubusercontent.com/linuxserver/docker-templates/master/linuxserver.io/img/mastodon-logo.png'
  -v '/mnt/disk1/docker-data-array/mastodon/':'/config':'rw,slave' 'lscr.io/linuxserver/mastodon:latest'

Container logs

D, [2025-10-20T18:53:44.055743 #400] DEBUG -- : [03805363-5b8f-4f5c-b715-acd027bd9679] Error fetching remote file: Error while optimizing 0b46c1d2ba8b23e88126430f6a9dd40820251020-400-p9cfns: VipsForeignLoad: "/tmp/0b46c1d2ba8b23e88126430f6a9dd40820251020-400-p9cfns.avif" is not a known file format

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[3000Neo]

As far as I can tell this error happens because the "vips" package used in this container doesn't support .avif pictures out of the box. To add support for .avif pictures the "vips-heif" package needs to be installed as well.

To test this I cloned the repository, added the "vips-heif" package to the Dockerfile, built the docker image locally and setup a container using that image. With this setup the pictures of the same posts now load successfully.