Receiving RTP packets after RTSP setup
I'm trying to stream RTP packets from an IP camera using Python.
I am able to send the describe, setup & play commands using RTSP protocol, however, I am unable to start streaming the actual videostream using RTP.
Here is the code:
import socket
def printrec(recst):
recs=recst.split('\r\n')
for rec in recs:
print rec
dest="DESCRIBE rtsp://admin:[email protected] RTSP/1.0\r\nCSeq: 2\r\nUser-Agent: python\r\nAccept: application/sdp\r\n\r\n"
setu="SETUP rtsp://admin:[email protected]/trackID=1 RTSP/1.0\r\nCSeq: 3\r\nUser-Agent: python\r\nTransport: RTP/AVP;unicast;client_port=60784-60785\r\n\r\n"
play="PLAY rtsp://admin:[email protected]/ RTSP/1.0\r\nCSeq: 5\r\nUser-Agent: python\r\nSession: SESID\r\nRange: npt=0.000-\r\n\r\n"
# .. here SESID will be substituted with the session id that SETUP returns us ..
ip="192.168.1.74"
s=socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect((ip,554))
s.send(dest)
recst=s.recv(4096)
printrec(recst)
# etc. then the same for the strins "setu" and "play"
....
Setup replies me:
RTSP/1.0 200 OK
CSeq: 3
Session: 1117448817;timeout=60
Transport: RTP/AVP;unicast;client_port=60784-60785;server_port=8214-8215;ssrc=40d35c30;mode="play"
Date: Mon, Jan 19 2015 11:10:08 GMT
So we have the client ports 60784 and 60785 and the server ports 8214 and 8215.
Next, play replies me:
RTSP/1.0 200 OK
CSeq: 5
Session: 1117448817
RTP-Info: url=rtsp://admin:[email protected]/trackID=1;seq=3539; rtptime=16026930
Date: Mon, Jan 19 2015 11:10:08 GMT
Next, what am I supposed to do in order to start receiving RTP packets? Open an UDP socket as follow .. ?
sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM) # UDP
sock.bind((ip, serverport))
sock.recv(4096)
But I get nothing .. (it stalls)
Excuse me my poor knowledge of sockets..!
Answer
So,
After heavy sessions of googling and wireshark-analysis, I came up with the right solutions.
I am posting the resulting demo-code here .. I thought it might be usefull for the community.
If you ever wanted to read ip-cams with python and dump the H264 stream into an edible file, this is the thing you're looking for.
Enjoy!
"""
A demo python code that ..
1) Connects to an IP cam with RTSP
2) Draws RTP/NAL/H264 packets from the camera
3) Writes them to a file that can be read with any stock video player (say, mplayer, vlc & other ffmpeg based video-players)
Done for educative/demonstrative purposes, not for efficiency..!
written 2015 by Sampsa Riikonen.
"""
import socket
import re
import bitstring # if you don't have this from your linux distro, install with "pip install bitstring"
# ************************ FOR QUICK-TESTING EDIT THIS AREA *********************************************************
ip="192.168.1.74" # IP address of your cam
adr="rtsp://admin:[email protected]" # username, passwd, etc.
clientports=[60784,60785] # the client ports we are going to use for receiving video
fname="stream.h264" # filename for dumping the stream
rn=5000 # receive this many packets
# After running this program, you can try your file defined in fname with "vlc fname" or "mplayer fname" from the command line
# you might also want to install h264bitstream to analyze your h264 file
# *******************************************************************************************************************
dest="DESCRIBE "+adr+" RTSP/1.0\r\nCSeq: 2\r\nUser-Agent: python\r\nAccept: application/sdp\r\n\r\n"
setu="SETUP "+adr+"/trackID=1 RTSP/1.0\r\nCSeq: 3\r\nUser-Agent: python\r\nTransport: RTP/AVP;unicast;client_port="+str(clientports[0])+"-"+str(clientports[1])+"\r\n\r\n"
play="PLAY "+adr+" RTSP/1.0\r\nCSeq: 5\r\nUser-Agent: python\r\nSession: SESID\r\nRange: npt=0.000-\r\n\r\n"
# File organized as follows:
# 1) Strings manipulation routines
# 2) RTP stream handling routine
# 3) Main program
# *** (1) First, some string searching/manipulation for handling the rtsp strings ***
def getPorts(searchst,st):
""" Searching port numbers from rtsp strings using regular expressions
"""
pat=re.compile(searchst+"=\d*-\d*")
pat2=re.compile('\d+')
mstring=pat.findall(st)[0] # matched string .. "client_port=1000-1001"
nums=pat2.findall(mstring)
numas=[]
for num in nums:
numas.append(int(num))
return numas
def getLength(st):
""" Searching "content-length" from rtsp strings using regular expressions
"""
pat=re.compile("Content-Length: \d*")
pat2=re.compile('\d+')
mstring=pat.findall(st)[0] # matched string.. "Content-Length: 614"
num=int(pat2.findall(mstring)[0])
return num
def printrec(recst):
""" Pretty-printing rtsp strings
"""
recs=recst.split('\r\n')
for rec in recs:
print rec
def sessionid(recst):
""" Search session id from rtsp strings
"""
recs=recst.split('\r\n')
for rec in recs:
ss=rec.split()
# print ">",ss
if (ss[0].strip()=="Session:"):
return int(ss[1].split(";")[0].strip())
def setsesid(recst,idn):
""" Sets session id in an rtsp string
"""
return recst.replace("SESID",str(idn))
# ********* (2) The routine for handling the RTP stream ***********
def digestpacket(st):
""" This routine takes a UDP packet, i.e. a string of bytes and ..
(a) strips off the RTP header
(b) adds NAL "stamps" to the packets, so that they are recognized as NAL's
(c) Concantenates frames
(d) Returns a packet that can be written to disk as such and that is recognized by stock media players as h264 stream
"""
startbytes="\x00\x00\x00\x01" # this is the sequence of four bytes that identifies a NAL packet.. must be in front of every NAL packet.
bt=bitstring.BitArray(bytes=st) # turn the whole string-of-bytes packet into a string of bits. Very unefficient, but hey, this is only for demoing.
lc=12 # bytecounter
bc=12*8 # bitcounter
version=bt[0:2].uint # version
p=bt[3] # P
x=bt[4] # X
cc=bt[4:8].uint # CC
m=bt[9] # M
pt=bt[9:16].uint # PT
sn=bt[16:32].uint # sequence number
timestamp=bt[32:64].uint # timestamp
ssrc=bt[64:96].uint # ssrc identifier
# The header format can be found from:
# https://en.wikipedia.org/wiki/Real-time_Transport_Protocol
lc=12 # so, we have red twelve bytes
bc=12*8 # .. and that many bits
print "version, p, x, cc, m, pt",version,p,x,cc,m,pt
print "sequence number, timestamp",sn,timestamp
print "sync. source identifier",ssrc
# st=f.read(4*cc) # csrc identifiers, 32 bits (4 bytes) each
cids=[]
for i in range(cc):
cids.append(bt[bc:bc+32].uint)
bc+=32; lc+=4;
print "csrc identifiers:",cids
if (x):
# this section haven't been tested.. might fail
hid=bt[bc:bc+16].uint
bc+=16; lc+=2;
hlen=bt[bc:bc+16].uint
bc+=16; lc+=2;
print "ext. header id, header len",hid,hlen
hst=bt[bc:bc+32*hlen]
bc+=32*hlen; lc+=4*hlen;
# OK, now we enter the NAL packet, as described here:
#
# https://tools.ietf.org/html/rfc6184#section-1.3
#
# Some quotes from that document:
#
"""
5.3. NAL Unit Header Usage
The structure and semantics of the NAL unit header were introduced in
Section 1.3. For convenience, the format of the NAL unit header is
reprinted below:
+---------------+
|0|1|2|3|4|5|6|7|
+-+-+-+-+-+-+-+-+
|F|NRI| Type |
+---------------+
This section specifies the semantics of F and NRI according to this
specification.
"""
"""
Table 3. Summary of allowed NAL unit types for each packetization
mode (yes = allowed, no = disallowed, ig = ignore)
Payload Packet Single NAL Non-Interleaved Interleaved
Type Type Unit Mode Mode Mode
-------------------------------------------------------------
0 reserved ig ig ig
1-23 NAL unit yes yes no
24 STAP-A no yes no
25 STAP-B no no yes
26 MTAP16 no no yes
27 MTAP24 no no yes
28 FU-A no yes yes
29 FU-B no no yes
30-31 reserved ig ig ig
"""
# This was also very usefull:
# http://stackoverflow.com/questions/7665217/how-to-process-raw-udp-packets-so-that-they-can-be-decoded-by-a-decoder-filter-i
# A quote from that:
"""
First byte: [ 3 NAL UNIT BITS | 5 FRAGMENT TYPE BITS]
Second byte: [ START BIT | RESERVED BIT | END BIT | 5 NAL UNIT BITS]
Other bytes: [... VIDEO FRAGMENT DATA...]
"""
fb=bt[bc] # i.e. "F"
nri=bt[bc+1:bc+3].uint # "NRI"
nlu0=bt[bc:bc+3] # "3 NAL UNIT BITS" (i.e. [F | NRI])
typ=bt[bc+3:bc+8].uint # "Type"
print "F, NRI, Type :", fb, nri, typ
print "first three bits together :",bt[bc:bc+3]
if (typ==7 or typ==8):
# this means we have either an SPS or a PPS packet
# they have the meta-info about resolution, etc.
# more reading for example here:
# http://www.cardinalpeak.com/blog/the-h-264-sequence-parameter-set/
if (typ==7):
print ">>>>> SPS packet"
else:
print ">>>>> PPS packet"
return startbytes+st[lc:]
# .. notice here that we include the NAL starting sequence "startbytes" and the "First byte"
bc+=8; lc+=1; # let's go to "Second byte"
# ********* WE ARE AT THE "Second byte" ************
# The "Type" here is most likely 28, i.e. "FU-A"
start=bt[bc] # start bit
end=bt[bc+2] # end bit
nlu1=bt[bc+3:bc+8] # 5 nal unit bits
if (start): # OK, this is a first fragment in a movie frame
print ">>> first fragment found"
nlu=nlu0+nlu1 # Create "[3 NAL UNIT BITS | 5 NAL UNIT BITS]"
head=startbytes+nlu.bytes # .. add the NAL starting sequence
lc+=1 # We skip the "Second byte"
if (start==False and end==False): # intermediate fragment in a sequence, just dump "VIDEO FRAGMENT DATA"
head=""
lc+=1 # We skip the "Second byte"
elif (end==True): # last fragment in a sequence, just dump "VIDEO FRAGMENT DATA"
head=""
print "<<<< last fragment found"
lc+=1 # We skip the "Second byte"
if (typ==28): # This code only handles "Type" = 28, i.e. "FU-A"
return head+st[lc:]
else:
raise(Exception,"unknown frame type for this piece of s***")
# *********** (3) THE MAIN PROGRAM STARTS HERE ****************
# Create an TCP socket for RTSP communication
# further reading:
# https://docs.python.org/2.7/howto/sockets.html
s=socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect((ip,554)) # RTSP should peek out from port 554
print
print "*** SENDING DESCRIBE ***"
print
s.send(dest)
recst=s.recv(4096)
print
print "*** GOT ****"
print
printrec(recst)
print
print "*** SENDING SETUP ***"
print
s.send(setu)
recst=s.recv(4096)
print
print "*** GOT ****"
print
printrec(recst)
idn=sessionid(recst)
serverports=getPorts("server_port",recst)
clientports=getPorts("client_port",recst)
print "****"
print "ip,serverports",ip,serverports
print "****"
s1=socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
s1.bind(("", clientports[0])) # we open a port that is visible to the whole internet (the empty string "" takes care of that)
s1.settimeout(5) # if the socket is dead for 5 s., its thrown into trash
# further reading:
# https://wiki.python.org/moin/UdpCommunication
# Now our port is open for receiving shitloads of videodata. Give the camera the PLAY command..
print
print "*** SENDING PLAY ***"
print
play=setsesid(play,idn)
s.send(play)
recst=s.recv(4096)
print
print "*** GOT ****"
print
printrec(recst)
print
print
print "** STRIPPING RTP INFO AND DUMPING INTO FILE **"
f=open(fname,'w')
for i in range(rn):
print
print
recst=s1.recv(4096)
print "read",len(recst),"bytes"
st=digestpacket(recst)
print "dumping",len(st),"bytes"
f.write(st)
f.close()
# Before closing the sockets, we should give the "TEARDOWN" command via RTSP, but I am feeling lazy today (after googling, wireshark-analyzing, among other-things).
s.close()
s1.close()