Top-and-bottom 3D format
The Top-and-bottom 3D format works similarly to Side-by-side 3D format to provide a 3D video stream with the two images (one for each eye) within an image stream, but rather than placing them horizontally as in that format, they are placed vertically in the image as transmitted, with the vertical dimension of the image compressed into half the size of the full image.
When seen in a non-3D-capable presentation, the images are shown one on top of the other, each with altered aspect ratio. The 3D decoding device would separate them into two images, expand the vertical size to the full size (resulting in an image of lower resolution in this direction), and show them in alternating frames.
Viewing of this format in 3D would involve wearing special glasses that alternately blank out each eye's view at the appropriate frame rate so that the left and right eyes see the frames intended for them.
This format hasn't been as heavily used as the side-by-side one.