Unofficially and completely at own risk, it has been found to be possible to watch the Test Channel as described on the BT website, on an AAISP provided FTTC line.
Example for Debian GNU/Linux
Have extracted some paramaters from pppd, this may not work correctly if there is more than one instance.
eval `tdbdump /var/run/pppd2.tdb | grep CALL_FILE | cut -d'"' -f2`
Add a route to the multicast group on the device upon which PPPoE runs, aimed at the openreach modem. Also found to work without legacy unicast IP by adding a route:
echo ip route add 220.127.116.11 dev $DEVICE
Play stream. Caveats : It starts when the network receives an IGMP join and stops with IGMP leave.
Relaying the stream
It may happen that the computer hosting PPPoE is in an inconvenient location for watching and that other networked devices should receive copies of the stream. For real use an IGMP proxy would be used but for first testing smcroute lets one try multicast even where clients don't send IGMP join and leave correctly, but this also means the stream has to be manually started and stopped.
For testing, using smcroute we can reflect the multicast to other attached networks. SMCroute does not configure the interface without a legacy IP, so can copy WAN address:
ifconfig $DEVICE $IPLOCAL
smcroute requires the source address, this was found with wireshark and could be subject to change, int0 and ext0 are example devices to copy multicast packets to, these could be internal vlans on a home network:
smcroute -a $DEVICE 18.104.22.168 22.214.171.124 int0 ext0
To actually start:
smcroute -j $DEVICE 126.96.36.199
smcroute -l $DEVICE 188.8.131.52
now ffmpeg, vlc or other client can be ran elsewhere on the internal network, if their ethernet interfaces do not have legacy ip addresses and the client does not specify an interface, use the ip route
This had been tested on several linux bridges for ebtables purposes, each on 802.1q vlan tags, on a managed ethernet switch where the other untagged port for PPPoE is connected to the openreach modem.