Hi @penguin,
what you are reporting about the depth “image” is expected.
The depth information are not good to be directly displayed because the “depth map” contains depth values in 16 bit format with values in the range [0,65535] corresponding to 0 m → 65,535 m.
All the GStreamer sinks display information in 8 bit format with a normalization in the full range, so the final result is not visually significant and all the frames will be essentially black.
If you write your own sink element that retrieves the depth information you will notice that the depth values are correct if associated to real measures in millimeters.
You also correctly notice many zero values, that are relative to not valid depth data, the same as inf or nan in float format.