Infrared (ir) spectroscopy is used to investigate the structural properties of a-SiC:H in a wide compositional range and as a function of film thickness. Hydrogen content NH increases considerably with increasing carbon fraction. For low carbon alloys this is mainly due to an increase of hydrogen bonded to silicon, incorporated in a mono- or dihydride form. Above Eg=2.3eV the proportion of hydrogen incorporated in C-H bonds increases considerably. Oxidation of high C alloys is observed. Converting experimental transmission exactly into absorption data yields thickness independent NH values. It is shown that the previously reported discrepancy between the hydrogen content calculated from ir and nuclear reaction techniques is an artifact of the ir analysis.