IR absorption spectra of gaseous CF4 mixed with Ar and He in the v4 band region are studied at the buffer gas pressures from 0.5 to 300 atm. The line mixing effect seems to influence essentially the band shape. The pressure induced broadening of the Q-branch is essentially less than that of individual rotation-vibration lines and depends on a buffer gas. The broadening coefficients for J-multiplex are determined. To make band shape calculations, we propose a model relaxation matrix taken as a linear combination of matrices for weak and strong collision limit cases. This model with one fitting parameter characterizing the intensity of collisions provides an appropriate description of the obtained data set.