diff --git a/functions/convert.fish b/functions/convert.fish
new file mode 100644
index 0000000..b0bbd52
--- /dev/null
+++ b/functions/convert.fish
@@ -0,0 +1,7 @@
+# convert <OLD_EXT> <NEW_EXT>
+# convert all files with old_ext to new_ext using ffmpeg
+function convert
+    for i in *.$argv[1]
+        ffmpeg -i "$i" (string replace -r '\.[^.]*$' ".$argv[2]" -- $i)
+    end
+end