A method, system and computer program product for creating dynamic custom headers and for controlling flow rate of Downstream External Physical layer Interface (DEPI) packets are described herein. The method comprises concatenating or fragmenting a packet descriptor of a DEPU packet based on one or more of associated packet size, maximum transmission unit, packet type, channel configuration information and flow control mode. The method further comprises creating a header for the packet based on data in a programmable header template and storing the header in a header buffer, determining whether to transmit the packet based on one of a flow meter or a maximum transmission unit size and transmitting the packet by sending the packet descriptor to an output direct memory access (DMA) controller. A flow meter flow control mode determines if a packet is to be transmitted based on packet size, bucket size, a low threshold and a high threshold. A maximum transmission unit flow control mode determines if a packet is to transmitted based on packet size and a maximum transmission unit size. The header can be customized for Packet Streaming Protocol (PSP) mode or Moving Picture Experts Group Transport Stream (MPT) mode and includes dynamic customizable fields such as User Datagram Protocol (UDP) port identification, flow identification and session identification.