Convert a WAV (Asterisk recordings) to MP3

This sounds like one of either:

• Firewall problem
• Nat problem

Either way, your RTP isn't getting through. I would suggest:

1. Trying it from a different location, where you are not behind a NAT router. If you have a separate router & broadband modem, plug your computer straight into the broadband (and reset it) and try that. If they are integrated, try setting the DMZ on the router to be you computer's local IP. You can also try port forwarding the RTP ports.

2. Double check your AWS security groups. If you haven't done it right it just won't work.

I've done this with Voxilla's FreePBX AMI and it worked perfectly (excluding CDR, which did not work).

I've used many versions of asterisk, with several different VoIP providers (SIP and one or two IAX2), physical cards on analog lines (Sangoma/Digium/Pika), and many different PC-based and hardphones (Aastra/Polycom/Sipura/Linksys/Snom/Mitel) and have never had that problem.

It's almost certainly your PSTN gateway. If it's an analog card, there's probably an extra wait at the end of the dial string, or a delay setting specific to the manufacturer. These cards mute the line while dialing, and that's probably what is happening here.