We do have a Function Field for Format Conversion - and one of the options there is Binary to Base64. In the Conversion Source field, you'd put a reference to your Origin field that contains the binary (byte array) data.
If you need to do this in script, we don't have a convenient way to do this for VBScript. However, if you use C# you can use the ToBase64String() method. A simple example would look like this:
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