Provide nginx example for advanced transcoding

#2814 (comment)

doc/run.rst

@@ -95,6 +95,12 @@ Nginx
 
 * Restart Nginx service
 
+Reverse proxies can also be used to handle really old devices and convert their request, e.g. to enable transcoding on http 1.0 protocol.
+The example only works in conjunction with the respective gerbera configuration and `iptables` settings.
+
+    .. literalinclude:: ../scripts/nginx/gerbera-transcode.conf
+
+
 .. index:: Sqlite
 
 Using Sqlite Database (Default)

scripts/nginx/gerbera-transcode.conf

@@ -0,0 +1,43 @@
+# iptables -t nat -A PREROUTING \
+#   -i <incoming network interface> \
+#   -p tcp --dport GERBERA_PORT \
+#   --src <client's IP> \
+#   --dst GERBERA_IP> \
+#   -j REDIRECT --to-port NGINX_PORT
+
+server {
+  listen GERBERA_IP:NGINX_PORT;
+
+  location / {
+    proxy_pass              http://GERBERA_IP:GERBERA_PORT/;
+
+    proxy_set_header        Host $host;
+    proxy_set_header        X-Real-IP $remote_addr;
+    proxy_set_header        X-Forwarded-For $proxy_add_x_forwarded_for;
+    proxy_set_header        X-Forwarded-Proto $scheme;
+    proxy_set_header        User-Agent "imperial DABMAN i250 (proxied by nginx)"; # Used for client filtering in Gerbera
+
+    proxy_http_version 1.1; # This is important :)
+  }
+}
+
+#  <clients enabled="yes">
+#    <client userAgent="imperial DABMAN i250" flags="TRANSCODING1" />
+#    <!-- Identify the requests by User-Agent string and flag them accordingly -->
+#  </clients>
+#  <transcoding enabled="yes">
+#    <mimetype-profile-mappings>
+#      <transcode mimetype="audio/ogg" client-flags="TRANSCODING1" using="profile"/>
+#    </mimetype-profile-mappings>
+#    <profiles>
+#      <profile name="profile" enabled="yes" type="external">
+#        <mimetype>audio/mpeg</mimetype>
+#        <dlna-profile>MP3</dlna-profile>
+#        <accept-url>no</accept-url>
+#        <first-resource>yes</first-resource>
+#        <accept-ogg-theora>no</accept-ogg-theora>
+#        <agent command="<path to shell script that does the actual transcoding>" arguments="%in %out" />
+#        <buffer size="1048576" chunk-size="131072" fill-size="262144"/>
+#      </profile>
+#    </profiles>
+#  </transcoding>