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Hydrides have long been considered promising candidates for achieving room-temperature su- perconductivity; however, the extremely high pressures typically required for high critical tem- peratures remain a major challenge in experiment. Here, we use high-throughput first-principles calculations to propose a class of high-Tc ambient-pressure superconductors with MH4 stoichiom- etry. These hydrogen-based compounds adopt the bcc PtHg4 structure type, in which hydrogen atoms occupy the one-quarter body-diagonal sites of metal lattices, with the metal atoms acting as chemical templates for hydrogen assembly. Through comprehensive first-principles calcula- tions, we identify three promising superconductors, PtH4, AuH4 and PdH4, with superconducting critical temperatures of 84 K, 89 K, and 133 K, respectively, all surpassing the liquid-nitrogen temperature threshold of 77 K. The remarkable superconducting properties originate from strong electron-phonon coupling associated with hydrogen vibrations, which in turn arise from phonon softening in the mid-frequency range. Moreover, ab initio molecular dynamics simulations demon- strate that PtH4 remains kinetic stable at 300 K over 20 ps, with no atomic diffusion observed. Our results provide crucial insights into the design of plausible structures with potentially novel properties, particularly in the search for high-Tc superconductors at ambient pressure