Both liveStream and LiveBroadcast are two different things, as defined on the youtube website. Therefore, the ID for them should also be different.
Livestreams
The liveStream resource contains information about the video stream that you upload to YouTube. The stream provides content that will be broadcast to YouTube users. After creating a liveStream, a resource can be mapped to one or more liveBroadcast resources.
USING stream.getId() you can get the video streaming id
Sample code in a link gives an idea of how to use it
Liveroadcasts
The liveBroadcast resource is an event that will be broadcast, through live video, on YouTube.
USING returnedBroadcast.getId().getId() you can get the broadcast id
Sample code in a link gives an idea of how to use it
Check Try It the part in which there is streamId where you can indicate which video you can associate with the broadcast.
Shaggy
source share