|UI location||Group: Sequencer|
|Current version download||https://github.com/mutantbob/blender-letterbox|
Pick a Scene, Image, or Movie strip in the Video Sequence Editor, and use the Strip menu to find the Letterbox submenu. Then choose the letterbox option you prefer. A transform effect strip will be created to accomplish the effect.
If there is already a Transform strip pointing at the active strip, or if the active strip is a Transform strip, then it will be adjusted instead.
This addon has adjustable parameters, but they are only visible if you have a 3D view open with its toolbar open (which is unlikely if you are doing sequence editing; maybe blender will be upgraded to show the operator parameter panel in another spot one day). The one menu entry that is a plain "Letterbox" reuses the align parameters from the last completed letterbox operation. The rest start with parameters that are initialized to accomplish the operation on the label.
The biggest shortcoming of this addon is that for strips that don't include specific aspect ratio information it assumes the target strip has square pixels. (Scene strips do have aspect ratio information and this addon uses it). Non-square pixels are not that unusual (especially for DVD content which is routinely 720x480 pixels, but a 16:9 aspect ratio instead). Until blender is upgraded to extract this information and store it on a sequence property, you can kludge around it by adjusting the display aspect ratio property on the operator.