Streaming Audio and Video

1
Streaming Audio and Video
60-520 Seminar Topic Instructor Dr. A. K.
Aggarwal Presented By Mostafa Monwar
2
What is Streaming Technology
A technique for transferring data such that it
can be processed as a steady and continuous
stream, client does not have to download the
entire file to view it.
Data
Source
Network
The portion in the buffer
The portion client is viewing
3
Advantages

• It reduces download time

• It provides steady service

• Slower systems can take advantage of streaming
  technology

• Provide service on demand

Applications are utilizing this technology are
Streaming Video, IP telephony, Internet Radio,
Distance learning, Videoconferencing,
Interactive games and so on
4
Disadvantages

• It is difficult to keep the service steady if
  the bandwidth is low

• The maintenance of streaming server is
  relatively expensive

• Packet loss may occur during the transmission

5
3 types of delivery methods of streaming media

• Streaming Stored Audio and Video

• Streaming Live Audio and Video

• Real-Time Interactive Audio and Video

6
Media Player or Helper Application
Three main streaming media companies or products
are RealPlayer (RealNetworks), Media Player
(Microsoft) and QuickTime (Apple).

• Three basic tasks of media players
• Decompression
• Jitter Removal
• Error Correction

7
Accessing Audio Video thru a Web server
Web Browser
HTTP
Web Server With Audio Files
Client
Files
Media Player
8
Accessing Audio Video thru a Meta File
Web Browser
HTTP request /response
Client
for meta file
Web Server
meta file
HTTP
Media Player
Audio/Video file requested and sent using HTTP
A meta file contains information of URL, type of
encoding, etc about the audio/video file that is
to be streamed.
9
RTSP Diagram
Web Browser
HTTP request/response
Client
Web Server
meta file
RTSP Streaming Command
Media Player
Streaming Server
RTP Audio / Video Content
HTTP is insufficient for user interaction. With
streaming server audio/video file can be sent
over UDP,
10
Protocols

• RTSP Real Time Streaming Protocol

• RTP Real-time transfer Protocol

11
RTSP

• RTSP is a industry standard Internet
  application level protocol

• RTSP is a framework for delivering and
  transmission of multicast data stream

• RTSP is a protocol that allows a media player
  to control the transmission of a media stream for
  exchanging control information

12
RTSP Message Format
Start Line Message Header Message Header
CRLF message body
Request-Line
Method SP Request-URI SP
RTSP-Version CRLF
Status-Line
RTSP-Version SP Status Code SP Reason
Phrase CRLF
Field-name field-value CRLF
Header
13
RTSP Features

• RTSP works in the conjunction with RTP to
  deliver streaming audio video content

• RTSP maintains a server state during
  transmission unlike HTTP

• Client-Server architecture

• Overcome the limitations of HTTP. RTSP enhance
  HTTP functions

• RTSP provides the synchronization of events

14
RTP

• RTP is used to transmit real-time data

• RTP encapsulate segments

Payload Sequence Timestamp Synchronization
Misc type number
source identifier
15
RTSP Operation
HTTP GET
Web Server
Web Browser
HTTP
Presentation Description File
Setup
Play
Media Player
Media Player
Media Stream
RTSP
Pause
Teardown
16
Presentation Description File
lttitlegt Music lt/titlegt ltsessiongt ltgroup
languageen lipsyncgt ltswitchgt lttrack
typeaudio ePCMU/8000/1 srcrtsp//audio.com
/music/audio.en/lofigt lttrack
typeaudio eDV14/16000/2 pt90
DV14/8000/1 srcrtsp//audio.com/music/audio.en
/hifigt lt/switchgt lttrack
typevideo/jpeg srcrtsp//video.com/music/vi
deogt lt/groupgt lt/sessiongt
17
Fixed Playout Delay
Playout Schedule p-r
Missed playout
Packets generated
Packet received
Playout Schedule p-r
r
p
p
18
Forward Error Correction
1
2
3
4
Original stream
1
1
3
2
2
3
4
Redundancy
Internet
4
3
1
1
LOSS
Received stream
2
4
1
2
3
Reconstructed stream
19
Interleaving
Original Stream
1 2 3 4
5 6 7 8
9 10 11 12
13 14 15 16
1 5 9 13
2 6 10 14
3 7 11 15
4 8 12 16
Interleaved Stream
Received Stream
1 5 9 13
2 6 10 14
LOSS
4 8 12 16
1 2 4
5 6 8
9 10 12
13 14 16
Reconstructed Stream
20
References
http//www.rtsp.org/ http//www.cs.helsinki.fi/u/j
manner/Courses/seminar_papers/rtsp.pdf http//www.
javvin.com/protocol/rfc2326.pdf http//www.cs.colu
mbia.edu/hgs/rtp/ James F. Kurose, Keith W.
Ross. Computer Networking, 2nd Edition, Addison
Wesley Longman, Inc, 2003. http//www.webopedia.co
m/TERM/R/RTSP.html
21
Any Questions