I came across this article (http://www.cisco.com/warp/public/788/pkt-voice-general/bwidth_consume.html)
that states there is a non-default version of g.729 which uses 30ms
packetization period, thus the RTP payload is 30bytes (I have just noticed that
now, I was under the impression that the payload was 20bytes).
Any idea what to do in this case?
From: ethereal-dev-bounces@xxxxxxxxxxxx
[mailto:ethereal-dev-bounces@xxxxxxxxxxxx] On
Behalf Of Alejandro Vaquero
Sent: Tuesday, July 25, 2006 4:41
AM
To: Ethereal development
Subject: Re: [Ethereal-dev]
Decoding G.729 using Ethereal, rtpdump and VoiceAgedecoder
Looks you are close because you get some voice
patterns. If the RTP packetization period is 20ms, then there are two 10byte
samples of G729 encoded data per RTP packet, so make sure when you run the
"rtpdump" the samples are in the correct order when generating the
bitstream.
Gabriel M. wrote:
Hi,
I am trying to decode a VoIP conversation using G.729
encoding. I have read older messages on this list (and others) but I am still
not able to dump a listenable .au file.
The steps that I made so far:
capture
the traffic using Ethereal and dumping the RTP data (Statistics -> RTP ->
Show all streams -> SaveAs).
Use
rtpdump (http://www.cs.columbia.edu/IRT/software/rtptools/)
to dump only the audio payload (“rtpdump -F payload -f in.rtp -o
out.rtp”)
Use
self-made code (see the code at the end of the e-mail) to convert the rtpdump
into the bitstream expected by the decoder
Decode
the bitstream using the VoiceAge decoder (decoder out.rtp test2.au)
Play
the test2.au using GoldWave, (with all possible combinations between 16bit
signed/unsigned 8000Hz)
Unfortunately all I can hear is some weird sound ( I
can see voice patterns in GoldWave, but the sound is metalic, almost
alien-like). Am I doing something wrong ?
References:
http://www.ethereal.com/lists/ethereal-dev/200505/msg00399.html
http://www.dsprelated.com/groups/speechcoding/show/666.php
//rtp_bitstream.c
[code]
#include <stdio.h>
int main(int argc, char **argv)
{
char c;
FILE *f=fopen("in.rtp", "r");
FILE *fileout = fopen("out3.rtp","w");
long lSize;
char * buffer, * out;
char qbyte, q;
int i, j =0, k;
fseek (f , 0 , SEEK_END);
lSize = ftell (f);
rewind (f);
buffer = (char*) malloc (lSize);
out = (char*) malloc (lSize * 16);
fread (buffer,1,lSize,f);
for (i = 0; i<lSize; i++)
{
qbyte = buffer[i];
for (k=0;k<8;k++)
{
q = qbyte & 1;
out[j] = 0x00;
j++;
if (q == 0)
out[j] = 0x71;
else
out[j] = 0x81;
j++;
qbyte >>= 1;
}
}
fwrite (out , 1 , lSize * 16, fileout);
return 0;
}
[/code]
Best regards,
Gabriel.
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