The content in a SMPTE 2110 source is always a set of streams consisting of one video asset, zero or more audio assets, and zero or more captions (ancillary data) assets. Each asset is in its own stream.
With SMPTE 2110 sources, the upstream system has already identitifed the assets required for the channel, and has listed these assets in the SMPTE 2110 SDP files. Therefore, you don't need to determine which assets you want to extract. But you do need to obtain some information about the assets. For more information, see Creating a SMPTE 2110 input.