Downloading and streaming assets are done through a httphandler in the api. The same handler is used both for download and streaming.
The easiest way to get a Download/stream url would be to call the GetAssets search as that contains already constructed urls
{
"success": true,
"error": "",
"total": "1",
"items": [{
"itemId": "23624",
"totalCases": "1",
"assetId": "3119",
"itemId": "23624",
"assetType": "4",
"fileSize": "4318504",
"name": "",
"thumb": "https://mm-dam.dev.digizuite.com/dmm3bwsv3/3119_3_11_4_11_0_faa9987b-7b2d-47de-ab3a-92993146a802_False.jpg?mptdid=96310",
"downloadSource": "https://mm-dam.dev.digizuite.com/dmm3bwsv3/3119_0_11_4_44_0_faa9987b-7b2d-47de-ab3a-92993146a802_True_.jpg",
"imagePreview": "https://mm-dam.dev.digizuite.com/dmm3bwsv3/3119_2_11_4_11_0_faa9987b-7b2d-47de-ab3a-92993146a802_False.jpg?mptdid=96309",
"videoPreview": "https://mm-dam.dev.digizuite.com/dmm3bwsv3/3119_10079_11_4_11_0_faa9987b-7b2d-47de-ab3a-92993146a802_False.mp4?mptdid=0",
"videoPoster": "https://mm-dam.dev.digizuite.com/dmm3bwsv3/3119_2_11_4_11_0_faa9987b-7b2d-47de-ab3a-92993146a802_False.jpg?mptdid=96309",
"sourceLocationPath": "\\\\DZ-DEV-APP01\\mmdev\\dmm\\Assets\\1-10000\\3101-3200\\3119\\3119_.jpg",
"importDate": "2017-12-19T15:54:23.990+01:00",
"importedBy": "SuperAdministrator",
"assetVersionId": "",
"isPublic": "1",
"neverExpire": "1",
"endDate": "2017-12-19T15:54:24.060+01:00",
"published": "1",
"writeAccess": "1",
"readAccess": "1",
"displayAssetId": 3119,
"displayitemId": 23624,
"displayName": "",
"displayAssetType": "4",
"displayFileSize": "4318504",
"displayImportedBy": "SuperAdministrator",
"displayImportDate": "2017-12-19T15:54:23.990+01:00"
}]
}