Generic Camera & camera.play_stream

I’m trying to use the camera.play_stream service for this Generic Camera:

camera:
  - platform: generic
    name: 'Cam1'
    still_image_url: http://192.168.1.224/cgi-bin/snapshot.cgi?chn=0&u=[LOGIN]&p=[PASSWD]

But I get the error:

Failed to call service camera.play_stream. camera.cam1 does not support play stream service

From the reading I’ve done, it appears this is because I don’t have a stream_source: as part of Cam1 config. However, I can’t find anything–no rtsp, nothing else other than the still_image_url: I listed above in my camera/NVR literature.

Is there any workaround? The official Generic Camera instructions indicate a template can be used, but I can’t find any literature on this whatsoever. Any help will be greatly appreciated. Thanks!