This paper investigates the relationship between two ways of analyzing streaming systems: trace analysis for dataflow programs with firing, and network calculus for network flows. While the former focuses on the structure of the dataflow computation while idealizing the interaction with the environment, the latter characterizes the temporal properties of flows of data, largely abstracting from the computations that connect them. In this work, we show how a trace analysis can be used to derive a description of communication behavior of a dataflow program in terms of network calculus, which is then applied to answering a question about the buffer sizing. The example being studied is an MPEG-4 video decoder. © 2014 IEEE.