[Freeswitch-users] How to get real-time rtp audio and video ports

[takashi higashi]

Hey guys,
I sent e-mail to freeswitch developer about how to get rtp packet with ffmpeg. and I asked to him below question.
How can I get rtp packet with ffmpeg? I want to trancoding real time rtp packet to motion jpeg and transfer node.js.
and then, he answered like this,
The following works for me:
ffmpeg -re -f lavfi -i aevalsrc="sin(400*2*PI*t)" -ar 8000 -f mulaw -f rtp rtp://127.0.0.1:6666
ffmpeg -i pcmu.sdp -acodec copy /tmp/a.wav
or 
ffmpeg -i bingbing.mp4 -an -vcodec h264 -filter:v scale=1280:720 -f rtp rtp://127.0.0.1:6668
looks like pcmu is not a valid codec for mp4, so I use aac
ffmpeg -i pcmu-264.sdp -acodec libfaac -vcodec copy /tmp/a.mp4

So I asked about what is 6666 ports? How can I get rtp real-time audio and video ports?
but I couldn't get answer...
Somebody help me, how to get real-time rtp audio and video ports? please.