In the field of video protection, selective encryption (SE) is a scheme which ensures a visual security of video by encrypting a small part of data. This paper presents a new SE algorithm for H.264/AVC in CAVLC mode. This algorithm controls the amount of encrypted alternative coefficients (AC) of the integer transform in the entropic encoder. Two visual quality measures, the peak signal-to-noise ratio (PSNR) and the structural similarity (SSIM), are used to measure the visual confidentiality level of each video frame and to regulate the amount of encrypted alternatives coefficients. This method can be applied on intra and inter frame video sequences.