1

WhatNOW: A System to Enable Videostream in a Mobile NetworkAlexandre Martini, Sandro Mourão, Wesley SilvaNokia Technology Institute, Manaus, Brazil

報告者：劉源蔁

2

IntroductionCommunication graphic

3

Software ArchitectureMobile Client Software

Server Description and Theory

4

Mobile Client SoftwareSymbian platform

Controllers CVideoPlayerUtility CVidePlayerUtility2 CVideoRecordingUtility

5

Mobile Client Software-Codecs Codecs As shows, the codec program is responsible

for the job of encoding and decoding the image video and audio data. When it comes to video, it is worth mentioning H.263 , Xvid and H.264.

The encoded video and audio data are streamed in a multimedia container format, such as MP4 (MPEG-4 Part 14) , 3GP or AVI (Audio Video Interleave) .

6

These requirements can be defined as Video quality and bandwidth; Complexity (number of computations carried by

the algorithm); Synchronization (support to other sources of

information such as speech), and Delay (time delay between the encoding of a

frame and its decoding at the receiver) .

Mobile Client Software-Data Compression

7

Server Description and Theory The analysis of the scenario above described shows

us two ways to provide audio/video content over the Web: ◦ Using a common Web server;◦ Streaming it from a Stream Media Server.

Let us analyze these two technologies considering three points of view:◦ Deploying◦ Hosting;◦ Delivering

8

Server Description and Theory Web Server

◦ 1.1 Progressive Download◦ 1.2 Embedding “Player”

Streaming from a Streaming Media Server◦ 2.1 Streaming Media Architecture◦ 2.2 Video compression◦ 2.3 QoS control◦ 2.4 Streaming Server◦ 2.5Media synchronization◦ 2.6 Security and Privacy

9

Web Server The original audio/video is compressed (encoded) into

a single media file, often Flash Video (FLV) or MPEG-4,and uploaded to a Web server just like a normal file.

Basically,there are two ways to deliver our media file: Progressive Download and Embedding “Player”.

10

Progressive Download The client player receives this file piece by piece and

starts to buffer until have a piece large enough to be played.

Progressive download uses Hyper Text Transport Protocol on top of the Transmission Control Protocol for communication between server and client

11

Embedding “Player” This approach has its limitations, to know:

◦ If our video is changed, it is necessary to reopen the wrapped file, embed the video again and republish everything;

◦ The entire file must be downloaded from the web server before video playback can begin;

◦ Some larger videos have problems with synchronization and duration;

12

Streaming from a Streaming Media ServerFlash Media Server (Adobe);

Windows Media Service (Microsoft);

Darwin Streaming Server (Apple – Open Source);

QuickTime Streaming Server (Apple – Commercial).

Helix Server (Real Networks).

13

Streaming from a Streaming Media Server Capture audio/video, by a camera/microphones integrated in a mobile equipment;

Raw video and audio are pre-compressed by their own algorithms. This still happens in the mobile equipment;

The media file is uploaded to a Streaming Media Server, using any available wireless network:

When the client request a streaming media, through a Web Server hosting the application to show the video to the audience, the Streaming Media Server retrieves compressed video/audio data;

Application layer QoS control adapts and adjusts media file bit-streams according to the network status and QoS requirements;

Transports protocol creates the packets with compressed bit-streams to send them to Internet. As usually, some packets can be lost or delayed

Packets successfully delivered to the receiver are decoded after transport layer and their audio/video are synchronized, then.

14

Streaming Media Architecture

15

Video compression It can be classified in two approaches: scalable and

non-scalable.

As the scenario will be set according to different demands of stream (latency, andwidth, access points) the MPEG-4 is proposed, as it uses a scalable mechanism called FGS (fine granularity scalability) .

16

QoS control Full: comparison between decoded video

sequence a the original, using an algorithm calculating the distortion;

Reduced: comparison between features calculated from the original and decoded video sequence;

No reference: observations only on decoded video and estimate the quality.

17

Streaming Server Set up a streaming server consist basically in having

three components◦ Communicator: involving two layers, Application and Transport. It

is used to link clients to the server;

◦ Operation System: it is mandatory that it satisfies the real-time requirements for this kind of application;

◦ Storage system: a large enough storage system to support whole streaming to be delivered.

18

Media synchronization There are three levels of synchronization related to

three semantic layers of multimedia data: ◦ Intra-stream synchronization, to avoid interruptions by pauses or

gaps;

◦ Inter-stream synchronization, which without this to skew between the streams may become intolerable.

19

Security and Privacy Since this application can provide access to the user’s

data in the mobile, for example: file system to share photos, images, texts and multimedia content, is mandatory for it to be safe.

Operating System - OS: our application is intended to run in Symbian OS 9.x .

Application level privacy: photos and videos will only be displayed to friends authorized by the user.

20

UI Concept The key issues driving customer-centeredweb-design

21

Message Screen HOME、 Friends、Wall、 Video Screen

Video Screen with a user transmission

22

SNS for Mobile Comparisons

23

Conclusion The server storage capacity is another thing to worry

about.

In the mobile client software, good progress has been made, with streaming of a short video between peers, but we are still facing errors when trying longer videos.

Our expectation is to continue the work and hopefully deliver a more complete and stable prototype.