diff --git a/docs/index.md b/docs/index.md
index 8466aa8..d402407 100644
--- a/docs/index.md
+++ b/docs/index.md
@@ -60,6 +60,17 @@ of RAM do we need? What are the other things we need to take into account and
 how can we reason about the requirements for video streaming between friends?
 We hope to document all this as we find out.
 
+### Icecast Format
+
+> What is Icecast, the program?
+>
+> Icecast is a streaming server, which can stream audio (and video) to
+> listeners/viewers. It supports Ogg (Vorbis, Theora), Opus, FLAC and WebM
+> (VP8/VP9), nonfree codecs/formats like MP4 (H.264, MPEG4), M4A, NSV, AAC and
+> MP3 might work, but we do not officially support those.
+
+So, we aim for [WebM](https://www.webmproject.org/).
+
 ### Setting up Icecast
 
 TODO.