==== quality_extension_descriptor

Defined by MPEG in <<ISO-13818-1>>.

[source,xml]
----
<quality_extension_descriptor field_size_bytes="uint8, required">

  <!-- between 1 and 255 metric codes to be provied (although only 7 are defined) -->
  <metric code="uint32, required"/>

</quality_extension_descriptor>
----
