Introduction to Aspect Ratios
The aspect ratio of a video is the difference between the height and the width of a video. If the aspect ratio is wrong, the image may appear stretched or squashed.

To support badly encoded content, Zoom Player supports multiple aspect ratio modes:

1. Fit to Window
   Disables aspect ratio and renders the video image across the entire display area.
2. Source Aspect Ratio
   The original video aspect ratio with no adjustments.
3. Derived Aspect Ratio
   The original video aspect ratio with automatic adjustments based on data in the media stream. This is the default and recommended Aspect Ratio mode for any content that is properly encoded and supports dynamic aspect ratio changes (when streaming).
4. Fullscreen 4:3
   This is a forced aspect ratio mode which forces any content to appear as fullscreen on 4:3 screens.
5. Widescreen 16:9
   This is a forced aspect ratio mode which forces any content to appear as fullscreen on 16:9 screens.
6. Anamorphic
   This mode stretches the source resolution vertically by 33.333% for display in Anamorphic devices (Anamorphic Lens Projectors for example). The percentage stretched can be relative to the derived aspect ratio or to the current video dimension.
7. Custom
   This mode defines a custom (user selected Aspect Ratio. By default the custom aspect ratio is 2.35:1.

Specify a Custom Aspect Ratio
These two values specify the Aspect Ratio used when the Aspect Ratio mode is set to "Custom".
Some sample Aspect Ratios:
4:3
16:9
16:10
1.85:1
2.35:1

Anamorphic Aspect Ratio is Relative to
When using the Anamorphic aspect ratio mode, the video can be stretched relative to its source aspect ratio or against the currently defined video dimensions.

Reset Aspect Ratio to "Derived" mode when opening a new media
Enabling this setting ensures that the video aspect ratio is reset to the preferred derived mode when opening a new media.

Use Source Relative Stretch to compensate for non-square pixel displays (affects all AR's)
Enable/Disable Source Relative Stretch (Pixel Aspect Ratio). See "Source Relative (Pixel Aspect Ratio) Values" for more information.

"Derived" mode Automatically Adjusts Aspect Ratio for badly encoded content
Media content is often encoded with a slightly offset aspect ratio. With this setting enabled and Zoom Player aspect ratio mode set to "Derived", Zoom Player attempts to automatically compensate for badly encoded Aspect Ratio by trying to fit it into 4:3 or 16:9 modes, as long as the Aspect Ratio compensation lies within a safe margin.

Restrict AR Adjustments to Height in Fullscreen / Zoom mode (disable this on 16:9 displays)
Zoom Player always ensure that the video image fits into the specified Width and Height as defined in the user interface (and presets). However, when playing certain video content (usually where the black bar on a widescreen video is encoded as part of the video) in the Anamorphic aspect ratio, this will cause the width of the video to shrink in order to maintain the video height. With this setting enabled, only the video height is adjusted in fullscreen/zoom mode, allowing the video to break out of the specified height value. This may not work well on widescreen display devices that squeeze 4:3 content. In such cases, you may want to disable this setting.

Setting window to Source Video Size compensates for Aspect Ratio
When setting the Zoom Player window to match the Source Video resolution, this setting instructs Zoom Player to take into account the current aspect ratio mode.

Support Anamorphic Matroska Files
Matroska files can contain Aspect Ratio information. Depending on the source filter (component) used to read matroska files, the aspect ratio can be handled by the component itself, or with this setting enabled, it can be handled by Zoom Player. You should leave this setting disabled unless playing matroska files displays video with an incorrect aspect ratio.

Source Relative (Pixel Aspect Ratio) Values
Source Relative Stretch, at times referred to as PAR (Pixel Aspect Ratio), allows adjusting the video display to make the aspect ratio appear correct on display devices where the pixels are not perfect squares (for example, a Plasma 16:9 TV with a resolution of 1024x768). You can use the Pixel Aspect Ratio calculator to feed in the dimensions and resolution of your display device and it will automatically fill in the correct Source Relative Stretch value.

You can limit the Source Relative Stretch feature to a specific monitor by specifying the monitor number in the "Use on monitor" field.

Pixel Aspect Ratio - Relative Stretch Calculator
The calculator tool helps entering the correct values for the "Source Relative Stretch" setting. Using this tool, you can easily compensate for displays with non 1:1 PAR (non-square pixels) such as widescreen displays with a resolution of 1024x768 (a popular resolution with older Plasma TVs).