In-situ vitrification and crystallization of a PdCuNiP metallic glass was investigated using synchrotron light X-ray diffraction. Distinct differences between the Bragg peaks appearing upon thermal annealing of the glassy phase and those appearing during solidification from the melt were detected. This observation indicates that the crystal phases which are in competition with the amorphous phase during rapid quenching are not always the same with those precipitating upon annealing, contrary to a general believe. Measurements during in-situ vitrification allowed the determination of structural changes in the supercooled liquid and glassy states using real-space atomic pair PDF(r) and radial RDF(r) distribution functions. The first PDF peak corresponding to the first nearest neighbor (nn) coordination shell has a pre-peak at low interatomic distance (r) which grows during cooling from the liquidus temperature to the glass transition in the supercooled liquid region. A reversible expansion of the nn distances in the first coordination shell is observed in the same temperature range. Crystallization of shear bands operating under compressive applied stress previously observed by transmission electron microscopy has been non-destructively detected by synchrotron X-ray microscopy in transmission. Analysis of crystal nucleation frequencies under hydrostatic pressure shows that crystal nucleation is more favorable under compression loading.