SIP Server: Configure Opensip+Media proxy(for example Asterisk PBX)

I need: opensip+media proxy(for example asterisk pbx). I need codec translation I need video codec and audio codec I need asterisk+opensip setup opensips act as load balancer and asterisk work as media gateway. possible do asterisk only. it will be simple, but harder add another server if needed. I need from you: setup of opensips with nat traversal and rtpproxy. it is more scalable variant, but without asterisk(codec translation). You can add asterisk support(only one video codec, but audio codec translation). i need you to setup dialling via 9xxx do via asterisk. so you can test both variants. I figure I need calling via asterisk as default, so you will change config for free. there almost no additional complexity. asterisk is pbx. opensips is sip proxy. asterisk can do full featured pbx. but can handle 200-300 calls. opensips can't do pbx features that require playback of files, but can handle few thousands of calls. Usualy complex system use both variants+some load balancing &failover