Camera stream to Fire TV

My SV3C camera works well with generic and ffmpeg platforms. The live view (stream) works in Lovelace UI for both:

- platform: generic
  verify_ssl: false
  name: entrance
  username: !secret cam1_user
  password: !secret cam1_pass
  authentication: basic
  still_image_url: !secret cam1_auto
  stream_source:   !secret cam1_rtsp12

- platform: ffmpeg
  name: entrance_ffmpeg
  input: !secret cam1_rtsp12_cred

Using Developer Tools, I can also send notifications to Fire TV, with camera photo snapshot attachments. I found no way so far to make camera stream appear on my Fire TV.

The camera rtsp stream works fine in VLC on my notebook but not on Fire TV. Calling this HA service for example, nothing happens and nothing recorded in (standard) log:

Any idea what could be missing? Do I maybe need to install something like VLC on FireTV?