Nonlinear phenomena that arise during the propagation of spin waves in thin ferromagnetic films under conditions of the simultaneous existence of three-wave and four-wave parametric processes have been investigated. Investigations have been performed for single-frequency and double-frequency regimes of excitation of intense spin waves. The spontaneous modulation instability of the monochromatic running spin wave has been revealed for the first time at frequencies at which three-wave decay processes are allowed. The pronounced generation of a periodic sequence of bright spin wave solitons has been observed under excitation of two monochromatic spin waves at the same frequencies.