UPDATE 2020-08-24: Just use youtube-dl. It does everything automagically and is maintained.

Real Time Messaging Protocol (RTMP) was initially a proprietary protocol developed by Macromedia for streaming audio, video and data over the Internet, between a Flash player and a server. Macromedia is now owned by Adobe, which has released an incomplete version of the specification of the protocol for public use.

Many media sites (N24, zdf, ard, ...) use rtmp streams to prevent people from downloading the videos. Well, there is a little command line tool which allows downloading rtmp streams. It is called rtmpdump and is available in the arch linux repositories.

To use rtmpdump you have to extract the required parameters from the html source code. For N24 it looks like this (it is really ugly!).

To use rtmpdump we need to set the -r, -W and -y parameters; with -o we can specify a filename. An explanation of these parameters could be found with rtmpdump -h. An appropriate rtmpdump call for the html code above would look like the following:

$ rtmpdump \
  -r "rtmp://pssimn24livefs.fplive.net:1935/pssimn24/" \  # <1>
  -W "http://www.n24.de/_swf/HomePlayer.swf?cachingVersion=2.66" \  # <2>
  -y "mp4:cm2013/cmp/e214/89ed/ac91/30c0/0a1db4af7089b0c05161ea2dcca58546_1000.mp4" \  # <3>
  -o "myvideo.mp4"

As you can see I have extracted these values from the source code of the website. For n24 it is:

_n24VideoCfg.flash.videoFlashconnectionUrl
_n24VideoCfg.flash.SWFUrl (prepend the baseurl!)
_n24VideoCfg.flash.videoFlashSource

For simplification I have written a little python wrapper which extracts these parameters from a given URL and builds the rtmpdump command line string:

import re
import sys
import subprocess
import urllib.request
from urllib.parse import urlparse


url = sys.argv[1]
url_parsed = urlparse(url)
response = urllib.request.urlopen(url)
html = response.read().decode()

regex = re.compile(
    r'<title.*?>(?P<title>.+?)</title>|'
    r'(?:_n24VideoCfg.flash.videoFlashconnectionUrl = )["\'](?P<param_r>.*)["\'];|'
    r'(?:_n24VideoCfg.flash.SWFUrl = )["\'](?P<param_W>.*)["\'];|'
    r'(?:_n24VideoCfg.flash.videoFlashSource = )["\'](?P<param_y>.*)["\'];|'
)

title = ''
rtmpdump_params = {}

for match in regex.finditer(html):
    typ = match.lastgroup

    if typ == 'title':
        title = match.group('title')
    elif typ == 'param_r':
        rtmpdump_params['-r'] = match.group('param_r')
    elif typ == 'param_W':
        rtmpdump_params['-W'] = match.group('param_W')
    elif typ == 'param_y':
        rtmpdump_params['-y'] = match.group('param_y')

subprocess.call([
    'rtmpdump',
    '-r', rtmpdump_params['-r'],
    '-W', url_parsed[0]  + '://' + url_parsed[1] + rtmpdump_params['-W'],
    '-y', rtmpdump_params['-y'],
    '-o', title + '.mp4'
])