You can attach audio, video or photos to Mastodon posts. To do this click on the attachment logo (which is a paperclip on the web, apps will usually have a photo icon).
Attachments can be:
-Up to four PNG, JPG or GIF images of 8 megabytes
OR
-One MP4, M4V, MOV or WebM video of 40 megabytes
OR
-One MP3, OGG, WAV, FLAC, OPUS, AAC, M4A or 3GP audio file of 40 megabytes
There is no length limit on audio or video, only a file size limit. Remember to add text descriptions for attachments!
@feditips
Need to look up how to embed remote media like pics and clips, it's gotta be similar
You can embed a lot of media by just including the link, for example links to Bandcamp albums or YouTube videos will automatically turn into embedded players.
(Having said that, embedding may not happen on some apps, but it will work on the web interface.)