Q:

block specific udp packet with iptables

Is it possible to block specific udp packet using iptables?

for example I want to block packet containing bd 65 like at line 3, that is a sequence number of RTP packet

A:

Yes, the iptables "u32" module will allow you to take action on bit/byte values at a given offset (even with variable-length headers).  The syntax is extremely ugly, but it will get the job done.  Search for "iptables u32" and you'll find details & examples.
The line would look something like this:
... -m u32 --u32 "44&0xFFFF=0xBD65" -j DROP

(grab a 4-byte chunk starting at offset 44, AND with 0xFFFF, compare with 0xBD65)

