On Mastodon, you can attach up to four images, or one video file, or one audio file when making a post. Click on the attachment icon which usually looks like a landscape 🌄 icon or paperclip 📎 to attach something to your post.
- Images can be PNG, JPG, HEIF, WEBP, AVIF or GIF (including animated GIFs). The maximum file size is usually 16MB per image.
- Video clips can be MP4, M4V, MOV or WebM files. The maximum file size is usually 99MB, but there is no limit on running time.
- Audio clips can be MP3, OGG, WAV, FLAC, OPUS, AAC, M4A or 3GP files. The maximum file size is usually 99MB, but there is no limit on running time.
File size limits may vary on different servers, but these are the documented defaults. Ask your server admin if you have problems with uploads. Note that if your server is unusually busy then file uploads may slow down or stop for a while.
The file size limits quoted above are from the official documentation. However, there’s some indcation in the source code that they’ve been raised in updates, so you may well find you can upload much larger files.
Making your posts accessible for blind or deaf people
Remember to add text descriptions to attached files before posting, so that they can be accessible to people with disabilities. You can do this by clicking Edit on the file before posting, or writing on top of the attachment itself on some apps. For video clips, remember to describe both the audio and video, so that both deaf and blind people are able to find out what’s going on.
How do I post GIFs in Mastodon?
There is no GIF picker built into Mastodon due to the federated nature of the Fediverse and the need to protect privacy. However, there are three methods for adding GIFs to Mastodon posts:
- If you post a link to GIF it will automatically be embedded when you post it, as if the GIF had been chosen from a picker.
- If you have the actual GIF file stored on your computer or phone, you can upload it as an image attachment.
- Some phones or tablets have a GIF picker built into their on-screen keyboard.
How long can the video or audio attachments be?
Any length! There is no time limit on video or audio, there’s only the file size limit. To post a longer file, reduce its quality so that it stays within the size limit.
How do audio files play?
Mastodon’s web interface and most of the apps have a built-in audio player, some of them with visualisers.
How do I set the artwork for audio?
After you’ve attached an audio file, click the Edit button and then choose an image for the artwork. If you don’t set an image, it will use your profile picture as artwork.
The description has disappeared from the audio file!
If you’ve added a text description to an audio file and it vanishes, add it again and it should remain there okay. There seems to be an intermittent bug that sometimes deletes descriptions from audio attachments when you first upload them.