Abstract: Relay devices and sink devices that provide synchronized audio and/or video outputs are described. A relay device receives a first communication packet from a source device. The first communication packet includes a data frame. A timestamp is generated. The timestamp is an estimate of a time at which content defined by the data frame will be “played.” A second communication packet is generated that includes the data frame and the generated timestamp. The second communication packet is transmitted from the relay device. In one implementation, the generated timestamp is received by a plurality of sink devices, and is used to synchronize output signals (e.g., sound and/or video images) of the sink devices. In another implementation, the generated timestamp is received by a sink device, and is used to synchronize an output signal of the sink device with an output signal of the relay device.