ffmpeg5 update: Document how to use ffmpeg in pipewire.

introduction/welcome/changelog.xml

@@ -44,6 +44,9 @@
     <listitem>
       <para>July 12th, 2022</para>
       <itemizedlist>
+        <listitem>
+          <para>[renodr] - Documented how to use ffmpeg with pipewire.</para>
+        </listitem>
         <listitem>
           <para>[renodr] - Fix building gegl with ffmpeg-5.x.</para>
         </listitem>

multimedia/libdriv/pipewire.xml

@@ -152,6 +152,11 @@ ninja</userinput></screen>
       pages. The optional dependencies for documentation need to be installed
       for this to work.
     </para>
+
+    <para>
+      <option>-Dffmpeg=enabled</option>: This switch enables using ffmpeg for
+      audio conversion as a SPA backend.
+    </para>
   </sect2>
 
   <sect2 role="content">