Thanks very much for the quick reply. I was surprised that I could not find mention of Sorensen here and Roku on their forums, so really appreciate the info.
I just got a GT120 NVidia card to add to the MacPro workstation but have not installed it yet. If I understand your reply correctly, with or without the GPU I will be ok if I switch the codec selection and create a custom profile using the Apple H.264 instead of Main Concept, and use the three data rates as reasonable choices for high, medium and low quality encodes.
I assume that if I do that and DO add the GPU that I will get some faster encode times.
Do the Sorensen Squeeze Progressive Streaming profiles have any applicability or are the Streaming Profiles all I need ?
The content is 16x9 SD which I understand in Roku terminology is HD, and a 4x3 version of the same content is termed SD. The MP4 default profiles that they offer for Progressive Streaming are 320p or 480p.
=====