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Voice Over IP Video/Audio Streaming: Domain Expertise

1. H.323 standard for video conferencing and point to point communications.
T.120 - Real time data conferencing protocol

Call signals and controls

• H.323 - Packet-based multimedia communications systems
• H.225 - call control protocol
• H.235 - security
• H.245 - media control protocol
• Q.931 - digital subscriber signaling
• H.450.1 - Generic functional protocol for the support of supplementary services in H.323

2. Voice Over IP

SIP, H.323.

3. Audio and Video Codecs, Compression Algorithms

Audio codecs

• G.711 - PCM audio codec 56/64 kbps
• G.722 - audio codec for 7 Khz at 48/56/64 kbps
• G.723.1 - speech codec for 5.3 and 6.3 kbps
• G.728 - speech codec for 16 kbps
• G.729 - speech codec for 8/13 kbps
• Windows Media Audio (WMA), MP3

Video codecs

• H.261, H.263, H.264 (MPEG4 Part 10)
• MPEG-2, MPEG-4
• Windows Media Video (WMV)

4. Software APIs, libraries

• Open H.323
• Microsoft Video for Windows, DirectShow, DirectX

5. Case Studies:

a. Video conferencing software.
The client/server software is intended for business and entertainment use. Software has two units - Windows/MAC client application and Windows/Unix server multipoint control unit (MCU) application. The video streams handled by server are distributed to the clients based on the demand. Clients may communicate with each other using a video conference chat room.

b. Point to point video chat software
c. Web-based video conferencing software

d. TV Tuner Project
XShift TV Tuner application is the fully DirectShow compliant software for PC with the MS Windows. This application provides the playback, recording and trimming of TV video programs video (that are stored in file buffer), which is received by PC TV tuner. Simple sliding control enables video playback (for TV program) that was received before. Time to store video depends on several parameters such as: predefined buffer size, size of output video, compression quality etc.

e. Reverse Bitmap Filter
Reverse Bitmaps is a DirectShow filter designed for reversing frames in the MPEG-1, MPEG-2 Streams. It was designed for playing back MPEG-1, MPEG-2 files in reverse order - from back to front. It is fully compatible with Moonlight-Elecard MPEG2 Video Decoder, Video Renderer, Overlay Mixer, Video Mixing Renderer 7 and Video Mixing Renderer 9.

f. IP-telephony system
Maxpro, Inc developed a software-hardware complex for making encrypted Internet calls to and from PSTN (Public Switched Telephony Network). Was used the following PC based hardware: PhoneJack and LineJack produced by QuickNet (USA).
This system is especially attractive for small/medium businesses as it requires minimal investments in hardware, most of which is standard inexpensive PC hardware. Nevertheless, the deployment of the standard ITU H323 protocol stack enables scalability needed to satisfy the demands of larger businesses.

Technologies used: C++ for Windows and Linux, OpenH323 (www.openh323.org), OpenSSL (www.openssl.org)

Copyright © 2007 Maxpro, Inc. All Rights Reserved.