what aspect ratios does ffmpeg support?

In the documentation ffmpeg has this:

`-aspect aspect'
Set aspect ratio (4:3, 16:9 or 1.3333, 1开发者_运维问答.7777).

Is this implying that it only supports those two aspect ratios or are those just examples for how to set the ratio?

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I think it means you can either supply it in the "X:Y" format or as a decimal.