PIX having some restriction for Streaming Media.
The fixup protocol rtsp command lets PIX Firewall pass RTSP packets. RTSP is used by RealAudio, RealNetworks, Apple QuickTime 4, RealPlayer, and Cisco IP/TV connections. PIX Firewall does not support multicast RTSP.
If you are using Cisco IP/TV, use RTSP TCP port 554 and TCP 8554:
fixup protocol rtsp 554
fixup protocol rtsp 8554
PAT is not supported with the fixup protocol rtsp command
PIX Firewall cannot perform NAT on RTSP messages because the embedded IP addresses are contained in the SDP files as part of HTTP or RTSP messages. Packets could be fragmented and PIX Firewall cannot perform NAT on fragmented packets.
RTSP inspection does not support PAT or dual-NAT. Also, PIX Firewall cannot recognize HTTP cloaking where RTSP messages are hidden in the HTTP messages.
Try this:
Disable RTSP protocol inspection as a workaround