Complex sentence: DVDs using anamorphic widescreen are analogous to anamorphic format film negatives (although technically, the two formats are very different), wherein the rectangular image captured by the camera lens is optically squeezed (horizontally) to fit inside the available area of standard filmstock.
Split into simpler sentences: DVDs using anamorphic widescreen are similar to the use of anamorphic format film negatives (although technically, the two formats are very different). In film the rectangular image captured by the camera lens is optically squeezed to fit the available area of standard filmstock.