The reason you can't capture the NBC live stream or replays is because it isn't a rtmp stream. It's I believe MPEG-TS (MPEG transport stream) that downloads a live or replay stream in segments of small files. In NBC's case - IPTV.
http://en.wikipedia.org/wiki/MPEG_transport_stream
Here's an example of one those segments I got from NBC through Opera Dragonfly (Developer Tools):
Response
HTTP/1.1 302 Found
Date: Sun, 29 Jul 2012 16:34:33 GMT
Pragma: no-cache
Expires: Fri, 01 Jan 1990 00:00:00 GMT
Cache-Control: no-cache, must-revalidate
Location:
http://r4---lax02s05.c.youtube.com/v...es&file=seg.ts
Content-Type: text/html; charset=UTF-8
Server: ClientMapServer
Content-Length: 817
X-XSS-Protection: 1; mode=block
X-Frame-Options: SAMEORIGIN
This segment is about 637KB. Segments vary in size and aren't necessarily sequential.
I hope that answers your questions!
