source: http://www.vrdmn.com/2015/01/get-all-office-365-video-channels.html
Office 365 has introduced 3 new portals recently: Videos, Groups and Delve. Behind the scenes, the architecture of Videos and Groups is such that each Video channel is a site collection and so is each Group. For Delve boards, each board is saved as a Tag and when you add a document to a board, the document is tagged with the name of the board.
If you are working on a solution for Office 365 and want to integrate Videos, Groups or Delve, here is how you can get a list of all of them using the SharePoint REST API:
1) Get all Office 365 Video Channels with REST API:
https://siteurl.sharepoint.com/_api/search/query?querytext='contentclass:sts_site WebTemplate:POINTPUBLISHINGTOPIC'&SelectProperties='WebTemplate,Title,Path'&rowlimit=50
2) Get all Office 365 Groups with REST API:
https://siteurl.sharepoint.com/_api/search/query?querytext='contentclass:sts_site WebTemplate:Group'&SelectProperties='WebTemplate,Title,Path'&rowlimit=50
3) Get all Delve Boards with REST API:
https://siteurl.sharepoint.com/_api/search/query?querytext='(Path:"TAG://PUBLIC/?NAME=*")'&Properties='IncludeExternalContent:true'&selectproperties='Path,Title'&rowlimit=50