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In the RenderMan Preferences there is now a section to specify controls for playblasting Playblasting from RenderMan in the viewport.
When selecting the Playblast RenderMan viewport icon, the above menu will pop up. This will take settings from the Maya Playblast window but also adds controls for Quality and viewing for "it". Pressing "OK" begins the Playblast process. Note that each image will reach the values selected under quality before moving to the next frame. Better quality may take significantly longer to render a playblast. For final quality renders, use the standard Batch Rendering options.