Term: Storage Aspect Ratio (SAR)
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Term: Storage Aspect Ratio (SAR)
- Definition:
SAR (Storage Aspect Ratio) is the width and height of a video frame expressed as a ratio. For example, a video frame with a width of 720 pixels and height of 480 pixels (720x480) would have a SAR of 3:2.
SAR can be calculated with the following equation: SAR = DAR / PAR
Note that some sources (including Wikipedia) suggest that "PAR is also known as sample aspect ratio and abbreviated SAR, though it can be confused with storage aspect ratio."
The three values related to aspect ratios are intertwined. SAR is an immutable value that is unchanging over time or unable to be changed. It is the size of the file. DAR is the rendering of the file, and PAR is what has changed to achieve that. In other words, PAR is adjusted in order to get the appropriate DAR from the given SAR of the file, as the pixel dimensions of a file (SAR) are immutable. If the desired DAR is different than the SAR, the PAR must be adjusted to be either larger or smaller than 1:1, which represents a perfectly square pixel. For example, a 720x480 file has a SAR of 3:2, but must be displayed with a DAR of 4:3 to be rendered properly. In this case, a PAR of 8/9 must be set in order for the file to be displayed properly, or in other worse, the pixels must be slightly taller than they are wide.
SAR is stored in the metadata of each video frame, and a decoder uses this information to adjust the video to account for how it was sampled and how it should render. Changes may result in stretched or squeezed images.
Typical values for SAR include:
- 2:1: An image with 200 pixels wide by 100 pixels high
- 22:15: An image with 704 pixels wide by 480 pixels high
- 4:3: An image with 640 pixels wide by 480 pixels high
- 5:4: A 576i video with 720 pixels wide by 576 pixels high
- 16:9: A video shot at 1280 pixels wide by 720 pixels high
- Category:
- Video
- Resource:
- PAR, SAR, and DAR: Making Sense of Standard Definition (SD) video pixels
https://bavc.org/par-sar-and-dar-making-sense-standard-definition-sd-video-pixels/ - FADGI Significant Properties for Digital Video
https://www.digitizationguidelines.gov/guidelines/sigpropvideo.html - See also:
- Pixel Aspect Ratio (PAR); Display Aspect Ratio (DAR); Aspect ratio