Pixel Aspect Ratio

Pixel aspect ratio (PAR) describes the shape of a single pixel. Modern formats use square pixels (1.0), but legacy standard-definition and some HD formats used non-square pixels, where each pixel is wider or taller than it is square. If a non-square clip is treated as square, the picture looks horizontally stretched or squeezed. NLEs apply PAR correction so the image displays at its true frame aspect ratio. Editors run into PAR mostly with old SD footage (like anamorphic DV or HDV), where circles can look like ovals if the ratio is misinterpreted. Setting the correct PAR in clip and sequence settings fixes the distortion. With almost all current cameras and delivery being square-pixel, PAR is now mainly an archival and conversion concern rather than a daily one.