Here are the settings I am using in Compressor to convert my 720p 960×720 footage to NTSC 14:9:
Under Video format:
(1) Change Video format to NTSC
(2)Change Aspect Ratio to 4:3
(3) Leave field dominance Progressive (why introduce interlacing on progressive footage?)
Under Geometry:
Source Insert (Cropping)
Crop to: Custom
Left: 45
Right: 45
Output Image Inset (Padding)
Padding: Custom
Top:34
Bottom:34
The source cropping was based on 720 pixels across (NTSC) rather than 960 (HD 960×720). So, if my video looks streched out when the compressor job is done, then I will need to recalcultae based on (960/720) * 45 = 60 pixels. I should have run a test clip but I felt confident so I didn’t. I’ll be back to say if I was right or wrong.