Pixel aspect ratio describes the shape of a stored video sample: its width relative to its height when displayed. Many modern computer images use square pixels, but some video formats store non-square samples. Display aspect ratio therefore depends on both stored dimensions and pixel aspect ratio. A file can have a numerical resolution that looks unusual yet still display correctly when its metadata is respected. This is distinct from the physical shape of individual panel pixels.
Pixel aspect ratio and Display aspect ratio
Display aspect ratio describes the final picture's shape; pixel aspect ratio describes each sample's shape.
Why stored width can be misleading
A picture stored as 720 by 576 samples does not automatically have a display shape of 720:576. Broadcast-derived formats can use a sample aspect ratio that tells the renderer to stretch those samples into a different intended composition. Ignoring that instruction can make people and objects look too narrow or too wide.
Metadata and scaling work together
The decoder exposes coded dimensions and relevant aspect metadata, then the renderer chooses a display rectangle. A transcoder may convert non-square samples into square pixels while preserving the same composition. Comparing resolution labels without examining the display shape can make a correct conversion appear to be an error.
Avoid repairing the wrong stage
A user-selected stretch mode may hide an incorrect aspect interpretation on one programme but distort every correctly tagged source. It is better to determine whether the error belongs to the media, player or output scaling. If source metadata is wrong, report the affected item and proportions rather than changing all channels permanently.
An illustrative example
An archive television clip looks unnaturally narrow in one player but normal in another. Both report the same stored dimensions. The second player applies the signalled sample shape correctly, demonstrating why encoded width divided by height is not always the intended display ratio.
Practical actions
- Inspect coded dimensions and sample/display aspect information where the player exposes it.
- Compare automatic aspect handling in another compatible player using the same source.
- Restore global stretch settings before reporting a source-specific metadata fault.