You can attach images, video files or audio files to Mastodon posts:
🖼️ Images can be PNG, JPG, HEIF, WEBP, AVIF or GIF (including animated GIFs)
📺 Video clips can be MP4, M4V, MOV or WebM files
🔈 Audio clips can be MP3, OGG, WAV, FLAC, OPUS, AAC or 3GP files
The maximum file size for each image is usually 16 MB, for video or audio it's usually 99 MB. There is no restriction on running time, just file size.
More info on attachments at https://fedi.tips/how-do-i-post-images-videos-or-audio-in-mastodon-what-can-i-attach-to-a-post-how-do-i-post-gifs
