Video transmission on wireless links usually requires some frame aggregation, so that the overhead due to the headers is not a too large percentage of the bit-stream. In such a situation, header error detection is essential, because any error in the header may cause a loss of several consecutive frames. The contributions of this paper are (i) an improved reception of the length field of the header and (ii) an improved Frame Synchronization (FS) algorithm for aggregated frames. The FS algorithm has the following characteristics: (i) it makes use of the implicit redundancies which are present in the headers, thus resulting in an efficient synchronization of the variable-length frames; (ii) Bayesian hypothesis testing is used to estimate the correct synchronization; (iii) the proposed algorithm performs estimation on-the-fly and does not require reading the whole bit-stream. A comparative performance evaluation with respect to previously proposed algorithms is provided in the context of WiMAX MAC.