Description
The goal of this project is to implement a streaming video server and client that communicate using
the Real-Time Streaming Protocol (RTSP) and send data using the Real-time Transfer Protocol (RTP).
Your task is to implement the RTSP protocol in the client and implement the RTP packetization in the
server.
We will provide you code that implements the RTSP protocol in the server, the RTP de-packetization
in the client, and takes care of displaying the transmitted video.
For the submission, all necessary files should be put into a folder named with your own unikey,
and a zip archive of this folder should be emailed to liwei@it.usyd.edu.au.
Task 1 Code
Client, ClientLauncher The ClientLauncher starts the Client and the user interface which you use
to send RTSP commands and which is used to display the video. In the Client class, you will need
to implement the actions that are taken when the buttons are pressed. You do not need to modify the
ClientLauncher module.
ServerWorker, Server These two modules implement the server which responds to the RTSP requests and streams back the video. The RTSP interaction is already implemented and the ServerWorker calls methods from the RtpPacket class to packetize the video data. You do not need to
modify these modules.
RtpPacket This class is used to handle the RTP packets. It has separate methods for handling
the received packets at the client side and you do not need to modify them. The Client also depacketizes (decodes) the data and you do not need to modify this method. You will need to complete
the implementation of video data RTP-packetization (which is used by the server).
VideoStream This class is used to read video data from the file on disk. You do not need to modify
this class.
Task 2 Running the code
After completing the code, you can run it as follows:
First, start the server with the command
1
COMP5416 Video Streaming
1 python Server.py server_port
where server_port is the port your server listens to for incoming RTSP connections. The standard
RTSPport is 554, but you will need to choose a port number greaterthan 1024.
Then, start the client with the command
1 python ClientLauncher.py server_host server_port RTP_port video_file
where server_host is the name of the machine where the server is running, server_port is the
port where the server is listening on, RTP_port is the port where the RTP packets are received, and
video_file is the name of the video file you want to request (create your own video file
movie.Mjpeg). The file format is described in Appendix section.
The client opens a connection to the server and pops up a window like this:
You can send RTSP commands to the server by pressing the buttons. A normal RTSP interaction goes
as follows:
1. The client sends SETUP. This command is used to set up the session and transport parameters.
2. The client sends PLAY. This command starts the playback.
3. The client may sendPAUSEif it wants to pause during playback.
4. The client sends TEARDOWN. This command terminates the session and closes the connection.
The server always replies to all the messages that the client sends. The code 200 means that the request
was successful while the codes 404 and 500 represent FILE_NOT_FOUND error and connection error
respectively. In this assignment, you do not need to implement any other reply codes. For more
information about RTSP, please see RFC 2326.
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Task 3 The Client
Your first task is to implement the RTSP protocol on the client side. To do this, you need to complete
the functions that are called when the user clicks on the buttons on the user interface. You will need to
implement the actions for the following request types. When the client starts, it also opens the RTSP
socket to the server. Use this socket for sending all RTSP requests.
SETUP
• Send SETUP request to the server. You will need to insert the Transport header in which you
specify the port for the RTP data socket you just created.
• Read the server’s response and parse the Session header (from the response) to get the RTSP
session ID.
• Create a datagram socket for receiving RTP data and set the timeout on the socket to 0.5 seconds.
PLAY
• Send PLAY request. You must insert the Session header and use the session ID returned in the
SETUP response. You must not put the Transport header in this request.
• Read the server’s response.
PAUSE
• Send PAUSE request. You must insert the Session header and use the session ID returned in the
SETUP response. You must not put the Transport header in this request.
• Readtheserver’sresponse.
TEARDOWN
• Send TEARDOWN request. You must insert the Session header and use the session ID returned
in the SETUP response. You must not put the Transport header in this request.
• Read the server’s response.
Note: You must insert the CSeq header in every request you send. The value of the CSeq header is a
number which starts at 1 and is incremented by one for each request you send.
Example
Here is a sample interaction between the client and server. The client’s requests are marked with C:
and server’s replies with S:. In this assignment both the client and the server do not use sophisticated
parsing methods, and they expect the header fields to be in the order you see below.
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1 C: SETUP movie.Mjpeg RTSP/1.0
2 C: CSeq: 1
3 C: Transport: RTP/UDP; client_port= 25000
4
5 S: RTSP/1.0 200 OK
6 S: CSeq: 1
7 S: Session: 123456
8
9 C: PLAY movie.Mjpeg RTSP/1.0
10 C: CSeq: 2
11 C: Session: 123456
12
13 S: RTSP/1.0 200 OK
14 S: CSeq: 2
15 S: Session: 123456
16
17 C: PAUSE movie.Mjpeg RTSP/1.0
18 C: CSeq: 3
19 C: Session: 123456
20
21 S: RTSP/1.0 200 OK
22 S: CSeq: 3
23 S: Session: 123456
24
25 C: PLAY movie.Mjpeg RTSP/1.0
26 C: CSeq: 4
27 C: Session: 123456
28
29 S: RTSP/1.0 200 OK
30 S: CSeq: 4
31 S: Session: 123456
32
33 C: TEARDOWN movie.Mjpeg RTSP/1.0
34 C: CSeq: 5
35 C: Session: 123456
36
37 S: RTSP/1.0 200 OK
38 S: CSeq: 5
39 S: Session: 123456
Client state. One of the key differences between HTTP and RTSP is that in RTSP each session has
a state. In this assignment you will need to keep the client’s state up-to-date. Client changes state
when it receives a reply from the server according to the following state diagram.
The server. On the server side, you will need to implement the packetization of the video data into
RTP packets. You will need to create the packet, set the fields in the packet header and copy the
payload (i.e., one video frame) into the packet.
When the server receives the PLAY-request from the client, the server reads one video frame from the
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file and creates an RtpPacket-object which is the RTP-encapsulation of the video frame. It then sends
the frame to the client over UDP every 50 milliseconds.
For the encapsulation, the server calls the encode function of the RtpPacket class. Your task is to
write this function. You will need to do the following: (the letters in parenthesis refer to the fields in
the RTP packet format below).
• Set the RTP-version field (V). You must set this to 2.
• Set padding (P), extension (X), number of contributing sources (CC), and marker (M) fields.
These are all set to zero in this assignment.
• Set payload type field (PT). In this assignment we use MJPEG and the type for that is 26.
• Set the sequence number. The server gives this the sequence number as the frameNbr argument
to the encode function.
• Set the timestamp using the Python’s time module.
• Set the source identifier (SSRC). This field identifies the server. You can pick any integer value
you like.
• Because we have no other contributing sources (field CC == 0), the CSRC-field does not exist.
The length of the packet header is therefore 12 bytes, or the first three lines from the diagram
below.
You must fill in the headerfields in the header bytearray of the RtpPacket class. You will also need to
copythepayload(givenasargumentdata)totheRtpPacket’spayloaddatafield.
The above diagram is in the network byte order (also known as big-endian). Python uses the same
byte order, so you do not need to transform your packet header into the network byte order. For more
details on RTP, please see RFC 1889.
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Twiddling the Bits. Here are some examples on how to set and check individual bits or groups of
bits. Note that in the RTP packet header format smaller bit-numbers refer to higher order bits, that
is, bit number 0 of a byte is 27 and bit number 7 is 1 (or 20). In the examples below, the bit numbers
refer to the numbers in the above diagram.
Because the header-field of the RtpPacket class is of type bytearray, you will need to set the header
one byte at a time, that is, in groups of 8 bits. The first byte has bits 0-7, the second byte has bits 8-15,
and so on.
To set bit number n in variable mybyte of type byte:
1 mybyte = mybyte | 1 << (7 – n)
To set bits n and n + 1 to the value of foo in variable mybyte:
1 mybyte = mybyte | foo << (7 – n)
Note that foo must have a value that can be expressed with 2 bits, that is, 0, 1, 2, or 3.
To copy a 16-bit integer foo into 2 bytes, b1 and b2:
1 b1 = (foo >> 8) & 0xFF
2 b2 = foo & 0xFF
After this, b1 will have the 8 high-order bits of foo and b2 will have the 8 low-order bits of foo. You
can copy a 32-bit integer into 4 bytes in a similar way.
Bit Example. Suppose we want to fill in the first byte of the RTP packet header with the following
values: V = 2 P = 0 X = 0 CC = 3
In binary this would be represented as
1 1 0 | 0 | 0 | 0 0 1 1
2 V=2 P X CC = 3
3 2^7 . . . . . . . . 2^0
Task 4 Additional Exercise
1. Calculate the statistics about the session. You will need to calculate RTP packet loss rate, video
data rate (in bits or bytes per second), and any other interesting statistics that you can think of.
2. The user interface on the RTPClient has 4 buttons for the 4 actions. If you compare this to
a standard media player, such as RealPlayer or Windows Media Player, you can see that they
have only 3 buttons for the same actions: PLAY, PAUSE, and STOP (roughly corresponding to
TEARDOWN). There is no SETUP button available to the user. Given that SETUP is mandatory in an RTSP-interaction, how would you implement that in a media player? When does the
client send the SETUP? Come up with a solution and implement it. Also, is it appropriate to
send TEARDOWN when the user clicks on the STOP button?
3. Currently, the client and server only implement the minimum necessary RTSP interactions and
PAUSE. Implement the method DESCRIBE which is used to pass information about the media
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stream. When the server receives a DESCRIBE-request, it sends back a session description file
which tells the client what kinds of streams are in the session and what encodings are used.
Proprietary MJPEG (Motion JPEG) format. In this assignment, the server streams a video which
has been encoded into a proprietary MJPEG file format. This format stores the video as concatenated
JPEG-encoded images, with each image being preceded by a 5-Byte header which indicates the bit
size of the image. The server parses the bitstream of the MJPEG file to extract the JPEG images on
the fly. The server sends the images to the client at periodic intervals. The client then displays the
individual JPEG images as they arrive from the server.
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