Wireshark and Continuation or non-HTTP traffic - http

Question

I'm writing some code to integrate an in-house app into a DVR to retrieve a video file. This is all reverse engineered as there isn't any official documentation, and I'm having trouble understanding the following sequence of events (captured by playing with the DVR's Android app).
936 72.985204 192.168.0.1 192.168.0.200 HTTP 468 POST /cgi-bin/supervisor/NetworkBk.cgi HTTP/1.1 (application/x-www-form-urlencoded)
937 72.985368 192.168.0.200 192.168.0.1 TCP 54 mit-ml-dev > 41859 [ACK] Seq=1 Ack=415 Win=65535 Len=0
938 73.933676 192.168.0.200 192.168.0.1 HTTP 275 HTTP/1.0 200 OK (video/mpeg4)
939 73.933983 192.168.0.1 192.168.0.200 TCP 54 41859 > mit-ml-dev [ACK] Seq=415 Ack=222 Win=15544 Len=0
940 74.004433 192.168.0.200 192.168.0.1 TCP 74 [TCP segment of a reassembled PDU]
941 74.004887 192.168.0.1 192.168.0.200 TCP 54 41859 > mit-ml-dev [ACK] Seq=415 Ack=242 Win=15544 Len=0
942 74.024669 192.168.0.200 192.168.0.1 HTTP 1346 Continuation or non-HTTP traffic
The HTTP POST requests the video file, which then results in an HTTP OK. I get confused as to what happens next. Isn't the request complete when the HTTP 200 is received? Why then is it continuing to receive TCP data and then getting a HTTP Continuation or non-HTTP traffic? The subsequent TCP packets contain the video file I'm intending to download. When I manually craft a HTTP POST I get the HTTP OK response and then I'm stumped.
This is the code I use to simulate the HTTP POST.
import requests
dc = {"action":"download", "start_time":"2013 7 1 13 59 00", "end_time":"2013 7 14 3 0", "num":"255", "ch":"5"}
r = requests.post("http://192.168.0.200/cgi-bin/supervisor/NetworkBk.cgi", data=dc, auth=(username, password))
This code gets the HTTP 200 OK response, how do I get to the Continuation or non-HTTP traffic? I'm new to this and so am unsure if I've provided enough details. I can provide the HTTP headers if that will help.
Addendum
This is the RAW response of the HTTP OK reply. As far as I can tell, there is nothing there about expecting extra content.
HTTP/1.0 200 OK
Date: Mon, 01 Jul 2013 15:01:34 GMT
nServer: Linux/2.x UPnP/1.0 Avtech/1.0
Expires: 0
Pragma: no-cache
Cache-Control: no-cache
Connection: close
Content-Type: video/mpeg4
Content-Length: 5
0
OK

Answer 1

Why then is it continuing to receive TCP data and then getting a HTTP
Continuation or non-HTTP traffic?
By default, when you make a request, the body of the response is downloaded immediately.
So in this case once the successful POST request is made the DVR will immediately start sending the video data over TCP - most probably as a H.264 Byte Stream. That would account for the non-HTTP traffic you are seeing.
This code gets the HTTP 200 OK response, how do I get to the
Continuation or non-HTTP traffic?
You can override this default behaviour and defer downloading the response body until you access the Response.content attribute with the stream parameter: You could then use something like r.iter_content to iterate over the response data in chunks and then write them to a file. e.g.
import requests
url = "http://192.168.0.200/cgi-bin/supervisor/NetworkBk.cgi"
dc = {"action":"download", "start_time":"2013 7 1 13 59 00", "end_time":"2013 7 14 3 0", "num":"255", "ch":"5"}
r = requests.post(url, data=dc, auth=(username, password), stream=True)
if r.status_code == 200:
with open(path, 'wb') as f:
for chunk in r.iter_content():
f.write(chunk)