Premiere Pro automatically attempts to preserve the
frame aspect ratio of imported assets, sometimes changing the pixel
aspect ratio, the frame dimensions, or both so that the asset does
not appear cropped or distorted when used in a sequence. Some assets
contain metadata that allows Premiere Pro to make the calculations
automatically and precisely. For assets lacking this metadata, Premiere
Pro applies a set of rules to interpret pixel aspect ratio.
When you capture or import NTSC footage with the ATSC frame size
of 704x480, the D1 frame size of 720x486, or the DV frame size of
720x480, Premiere Pro automatically sets the pixel aspect ratio
for that asset to D1/DV NTSC (0.91). When you capture or import
footage with the HD frame size of 1440x1080, Premiere Pro automatically
sets the pixel aspect ratio for that file to HD 1080 Anamorphic
(1.33). When you capture or import PAL footage with the D1 or DV resolution
of 720x576, Premiere Pro automatically sets the pixel aspect ratio
for that file to D1/DV PAL (1.094).
For other frame sizes, Premiere Pro assumes that the asset was
designed with square pixels and changes the pixel aspect ratio and
frame dimensions in a way that preserves the asset image aspect
ratio. If the imported asset is distorted, you can change the pixel
aspect ratio manually.
When you drag an asset into a sequence, Premiere Pro centers
the asset in the program frame by default. Depending on its frame
size, the resulting image could be too small or overcropped for
the needs of the project. If so, you can change its scale. You can
do this manually or have Premiere Pro do it automatically whenever
you drag an asset into a sequence.
It is always a good idea to make sure that files are interpreted
correctly. You can read asset frame dimensions and pixel aspect
ratio near the preview thumbnail and in the Video Info column of
the Project panel. You can also find this data in the asset Properties
dialog box, the Interpret Footage dialog box, and the Info panel.