The self-generation of microwave magnetic envelope solitons in magnetic films has been realized for the first time. Solitons with a width of 20 ns and a carrier frequency of 5.1555 GHz were generated for the magnetostatic backward volume wave (MSBVW) configuration in a $5.2\ensuremath{\mu}\mathrm{m}$ thick yttrium iron garnet film. The film and MSBVW propagation structure were part of a ring with an overall gain of $+4\mathrm{dB}$. Pulse modulation at 10 MHz provided the interrupted feedback and the active mode locking which was needed to produce a stable and continuous stream of self-generated soliton pulses. Pulse width and phase measurements confirmed the soliton nature of the self-generated pulses.