Oops, the tag is ENCODER not ENCODED-BY.

doc/draft-terriberry-oggopus.xml

@@ -761,7 +761,7 @@ No terminating NUL octet is required.
 <vspace blankLines="1"/>
 This tag is intended to identify the codec encoder and encapsulation
  implementations, for tracing differences in technical behavior. The
- user-facing encoding application can use the 'Encoded-by' user commment
+ user-facing encoding application can use the 'ENCODER' user commment
  tag name to identify themselves.
 <vspace blankLines="1"/>
 </t>