I tried the experiment, but it didnt work.
Voipong seemingly identify g729 packages of 8khz (and put it as part of the output filename: session-enc18-G729-8KHz-....). I modified voipong to write the length before the payload. I am attaching part of the hexdump -C output of the raw file. (the length is multiplied by 2). Is data correct??. Can data with length=28 be 3 active G729D frames and 2 SID frames???
As I see your hex dump you are wrong when write payload data in voipong. There are 8 packets In your file. At the end of every packetI see two padding bytes "00 02". Last byte shows how many padding bytes are present in packet (if padding bit in header equals 1). Pls, verify paddind bit in RTP header ("rtp->pad" in voipong) and removethese bytesfrom payload and payload length. In your case payload length will be 26 bytes.
Igor S. Belyakov