DVD-A was shorthand for DVD Architect the software for this forum.

I am asking about a Blu-Ray. The defaults for DVD Architect are:

18 mbps
1920 by 1080

and 24 progressive for the frame rate. I'm wondering why the frame rate default is 24?

The default frame rate under File/Properties/Disk Properties/Frame Rate changes to match the Project Video Format you select when you start a new project. You told the software what kind of disk you want to make, DVD Architect sets the default and will render video and audio to match if your assets don't match your Project Video Format or Project Audio Format or if the project won't fit on the disk.

If you wish to test this: start a project with all of the possible frame rates and check under File/Properties/Disk Properties/Frame Rate for each type of BD project.

Don't get too hung up on it because you should be preparing your video and audio assets in Vegas using the MainConcept MPEG-2 or Sony AVC for Blu-ray templates.

* See DVD Architect 5.2 Manual pages 191-195 Rendering Files for Your Project.

Using the templates in Vegas will produce video and audio files that will pass through DVD Architect without rendering again. Vegas will likely render quicker given its use of all cores and video card render assist through Open CL and you will be better able to customize the templates to suit your needs.

If you have 24fps shot in a video camera- edit in a 24fps project in VegasPro - output a 24P (progressive) video stream from VegasPro for DVD Architect input - and finally create an authored Blu-Ray project in 24P form - that is what is meant by the above forementioned workflow. Your burned Blu-ray disc will play in standard players attached to modern widescreens (LCD/LED) as a 24P encoded video.

Most prosumer/consumer video will be shot as 60i, workflowed through the edit and authoring process as 60i - and your output is standard television signal played on old and modern TV's.