The process in which a cell becomes capable of differentiating autonomously into a myoblast in an environment that is neutral with respect to the developmental pathway. Upon specification, the cell fate can be reversed. A myoblast is a mononucleate cell type that, by fusion with other myoblasts, gives rise to the myotubes that eventually develop into skeletal muscle fibers. [ http://purl.obolibrary.org/obo/CL_0000056 ]