QOS design questions

a couple questions about qos. Currently we do no qos we are not voip. Our design is as follows
3560 access layer switches vlans ride along layer 2 until they get to our core switch where all the routing takes place(vlan interfaces). We have a flexwan card in our core that routes our wan over an mpls network. We want to do qos on video traffic. We can mark the traffic at layer 2 at the switchport the equipment automatically marks its cos packets.
now to my question
1) since the traffic is layer 2 until it hits the core and marked as cos where exactly do i do a cos-dscp map i am assuming it is on our 6509(ios). We need to convert the cos markings to dscp to route accross the mpls.
2) when exactly does the mapping come into place. Lets say 2 phones are on a lan on the same subnet cos markings will stay the same. What happens when 2 phones are on the same lan but different subnets does the mapping convert the cos to dscp since it is then getting routed
3)Will i also have to remap the packets to follow our mpls qos mappings.
3560 access layer switches vlans ride along layer 2 until they get to our core switch where all the routing takes place(vlan interfaces). We have a flexwan card in our core that routes our wan over an mpls network. We want to do qos on video traffic. We can mark the traffic at layer 2 at the switchport the equipment automatically marks its cos packets.
now to my question
1) since the traffic is layer 2 until it hits the core and marked as cos where exactly do i do a cos-dscp map i am assuming it is on our 6509(ios). We need to convert the cos markings to dscp to route accross the mpls.
2) when exactly does the mapping come into place. Lets say 2 phones are on a lan on the same subnet cos markings will stay the same. What happens when 2 phones are on the same lan but different subnets does the mapping convert the cos to dscp since it is then getting routed
3)Will i also have to remap the packets to follow our mpls qos mappings.