The reaction dynamics of vinyl bromide decomposition in perfect, face-centered cubic xenon and krypton matrices at 12 K and in xenon lattices with 10 and 20% vacant sites are computed using trajectory methods with an analytic potential for the electronic ground state of vinyl bromide. The total potential is written as the summation of a pairwise lattice potential, pairwise lattice-vinyl bromide interactions, and the gas-phase vinyl bromide potential. Product yield ratios, rate coefficients for vibrational energy transfer to the lattice phonon modes, and total decomposition rate coefficients are computed as a function of initial vinyl bromide energy. At low levels of excitation, three-center HBr dissociation is the only observed decomposition channel. This result is in accord with the data obtained from recent photolysis experiments. At higher energies, three-center HZ elimination becomes important. When the excitation energy exceeds 6.0 eV, three-center H-2 elimination becomes the major reaction channel. The relative importance of C-Br and C-H bond cleavage to produce Br and H atoms is greatly reduced in the matrix environment. Such processes become important only at higher energies. Molecular hydrogen elimination is also suppressed by the matrix, but the relative yield of HBr is enhanced compared to the gas-phase result. Limited calculations using Kr matrices suggest that the results are insensitive to matrix composition. The energy transfer rate coefficients are found to decrease exponentially with the percentage of vacancies in the lattice. The total vinyl bromide decomposition rates increase as the percentage of lattice vacancies increases, but the gas-phase rates are not approached even when 20% of the lattice sites are vacant. It is concluded that the molecular hydrogen seen in the matrix photolysis of vinyl bromide is produced by photolytic reactions of the HBr/acetylene products produced by the primary decomposition.