Both legacy networking technology and SDN APIs generally do not allow for highly precise timing of changes in data plane forwarding behavior. This can complicate the network processing of real-time synchronous data streams. For example, in the case of media flows, flow changes may be required to occur on the boundary of atomic elements such as video frames, requiring actions to be timed on the order of microseconds. Most SDN APIs and legacy networking tools do not allow for the changing of forwarding rules with a temporal accuracy of less than tens of milliseconds. To achieve precise timing of actions, the relatively slow and temporally imprecise process of establishing new data plane forwarding behavior can be decoupled from the actual timing of payload-aware flow changes. A proof-of-concept was developed to demonstrate seamless "clean" switching of uncompressed HD video (transported in UDP multicast RTP streams) using an off-the-shelf Ethernet switch and SDN techniques. In this PoC, specialized controller software uses SDN to prepare the network with new data-plane forwarding behavior, and then causes "source-timed" changes at a precise time in the flow's packet headers to match the new forwarding rules. Old forwarding rules that no longer match the new header values are then removed from the network.