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.
