HAT development and experiment

2002. 1. 24.

Kyoungae Kim, SNU Koreadrizzle@mmlab.snu.ac.kr

Outline• HAT ?• Software design • Implementation details• Experimental result• Future work

What’s HAT ?

HAT ?• High-quality Audio conferencing Tool

– Audio conferencing tool using mp3 codec• Variable bitrates: e.g., 32, 80, 128kbps

– Supports IPv4 and IPv6 : unicast and multicast– Supported OS : Windows 2000

• Working on MSR IPv6 stack• Will work on MSDN IPv6 stack

Software Design

Software ComponentsSounddevice

Encoderprocess

Stdin

RTP send

Wave data

PIPE

Stdout

Mic process

rawPCM

voice

RTPRecvprocess

Stdout

PIPE mp3 datamp3 data

Sounddevice

sound

Stdin

Decoderprocess

RTP headerRTP header

mp3 datamp3 data

RTP headerRTP header

Sender Receiver

At Sender• MIC process

– audio signal WAV file• Encoder process

– WAV file MP3 data ( LAME )– MP3 data RTP payload – Send it as a UDP packet

At Receiver• Receiver process

– RTP data MP3 data– Maintain participant information and statistics

in source database with RTCP

• Decoder process– MP3 data sound device ( mpg123 )

Implementation Details

Inter-Process Comm.

-check the condition of every process dies or not

-If no response, show error msg.

Statistics

Options

- Adjust bitrate

- Adjust system performance

- Input participant name

Message Exchange

UI

Receiver

1. Cre

ate P

roce

ss

ASK_ALIV

E

ALIVE,

SESS

ION_IN

FO

Encoder

2. Create Process

3 ASK_SSRC, Source Report

4.MY_SSRC

ASK_ALIVEALIVE

2.AFX_BEGIN_THREAD MIC

PIPE

PIPEPIPE 5._ popen

Decoder

Experimental result & Future work

Experiment environmentETRI

Daejeon

SNU Seoul

APAN-KRAPAN-KR(KOREN)(KOREN)Native Native IPv6 NetworkIPv6 Network

Result – bandwidth• PCM (Pulse Code Modulation )

– sample 16bit, two stereo, sampling rate 44.1kHz

– 16 * 141000 * 2 =~ 1.3 Mbps • MP3 encoding

– sample 16bit, two stereo, sampling rate 44.1kHz

– 128 – 256 kbps

Result – delay• Required maximum delay : 200 ~

300ms• Delay of HAT : 800 ~ 900ms• Solution to minimize delay

– Optimization of mpg123 for HAT tool• Delete useless options

– Optimization for real-time data• Modify buffer size, frame size

Future Work• Reduce end-to-end delay• Develop MSDN IPv6 version

• Welcome your participation in experiment of HAT and collaboration

• You can get more information from http://mmlab.snu.ac.kr/~hat