docs: add official ffmpeg docs reference

Author: lidel

src/ipips/ipip-0280.md

@@ -81,7 +81,7 @@ FFMPEG's libavformat supports both `$HOME/.ipfs/gateway` file and `IPFS_GATEWAY`
 ([ffmpeg.git/commit/f889837](https://git.ffmpeg.org/gitweb/ffmpeg.git/commit/f889837e00d3b2388a24c0a9d075ad62f47da825)).
 
 
-Ref. <https://blog.ipfs.tech/2022-08-01-ipfs-and-ffmpeg/>
+Ref. <https://ffmpeg.org/ffmpeg-protocols.html#ipfs>, <https://blog.ipfs.tech/2022-08-01-ipfs-and-ffmpeg/>
 
 #### Curl