Python knowledge? ustream script

#!/usr/bin/env python
# This script finds the rtmpdump command syntax for opening a UStream stream.

import sys
import urllib2
import re


def getVideoData(url):
# Get the HTML contents
req = urllib2.Request(url)
response = urllib2.urlopen(req)
html = response.read()

# Extract the channel ID from the HTML
channelId = None
m = re.search("Channel\sID\:\s+(\d+)", html)
if (m):
channelId = m.group(1)

# Extract the channel title from the HTML
channelTitle = None
m = re.search("property\="og\:url"\s+content\="http\:\/\/www." +
"ustream\.tv\/(?:channel\/)?([^"]+)"", html)
if (m):
channelTitle = m.group(1)

amfContent = None
if (channelId):
amfUrl = ("http://cdngw.ustream.tv/Viewer/getStream/1/"
+ channelId + ".amf")
response = urllib2.urlopen(amfUrl)
amfContent = response.read()

rtmpUrl = re.search("(rtmp\:\/\/[^\x00]+)", amfContent).group(1)
f = open('tmp.txt', 'w')
f.write(amfContent)
streamName = re.search("streamName(?:\W+)([^\x00]+)",
amfContent).group(1)

return (channelId, channelTitle, rtmpUrl, streamName)


def getRtmpCommand(rtmpUrl, streamName):
result = ("rtmpdump -v -r "" + rtmpUrl + "/" + streamName + """
" -W "http://www.ustream.tv/flash/viewer.swf" --live")
return result


def main(argv=None):
# Process arguments
if argv is None:
argv = sys.argv[1:]

usage = ("Usage: ustreamRTMPDump.py <ustream channel url> [filename]\n"
"e.g. "ustreamRTMPDump.py 'http://www.ustream.tv/ffrc'"")

if (len(argv) < 1):
print usage
return

# Get RTMP information and print it
url = argv[0]
print "Opening url: " + url + "\n"

(channelId, channelTitle, rtmpUrl, streamName) = getVideoData(url)
print "Channel ID: " + channelId
print "Channel Title: " + channelTitle
print "RTMP URL: " + rtmpUrl
print "RTMP Streamname: " + streamName + "\n"

rtmpCmd = getRtmpCommand(rtmpUrl, streamName)
print "RTMP Command:\n" + rtmpCmd

if __name__ == "__main__":
main()

Traceback (most recent call last):
File "S:ustreamRTMPDump.py", line 76, in <module>
main()
File "S:ustreamRTMPDump.py", line 66, in main
(channelId, channelTitle, rtmpUrl, streamName) = getVideoData(url)
File "S:ustreamRTMPDump.py", line 41, in getVideoData
return (channelId, channelTitle, rtmpUrl, streamName)
UnboundLocalError: local variable 'rtmpUrl' referenced before assignment

local variable 'rtmpUrl' referenced before assignment