It's a little bit of manual work, but you can also do this directly in VEGAS Pro.
Create a new Region (make a time selection and press R to insert region markers) every 30 seconds. Once those are in place, choose Tools | Scripting | Batch Render.In the Batch Render dialog, make all your file type and location choices and then select the Render Regions radio button. Click OK. Each region will be rendered to a separate file.
@Nathanael-ALLAL, you could also write your own script to do this. There's several rendering tutorials on my website. This one talks about rendering regions but you could modify the code to render the 30 second increments without actually needing to create the regions.