I did it. I defeated the horrible Google Home "cast-start" prompt sound!

[TheFes]

@markdavidoff

alias: Google Speaker Play
mode: parallel
icon: mdi:cast-audio
description: >-
  Plays media (on Google Speakers) at the specified volume without the extra
  bleeps and bloops. Restores the state back after it is done.
fields:
  playback_entity:
    name: Playback Entity
    description: The entity that will play the sound
    required: true
    selector:
      entity:
        domain: media_player
  playback_volume:
    name: Volume
    description: Volume to play the sound at
    required: false
    selector:
      number:
        min: 0
        max: 100
        step: 10
        unit_of_measurement: percent
        mode: slider
  media_location:
    name: Content ID
    description: The ID of the content to play. Platform dependent.
    example: media-source://media_source/local/folder_name/file.wav
    required: true
    selector:
      text: null
  media_type:
    name: Content type
    description: >-
      The type of the content to play. Like image, music, tvshow, video,
      episode, channel or playlist.
    example: media-source://media_source/local/folder_name/file.wav
    required: true
    default: music
    selector:
      text: null
sequence:
  - service: scene.create
    data:
      scene_id: before_state_{{ playback_entity|replace(".", "_") }}
      snapshot_entities: '{{ playback_entity }}'
  - service: media_player.volume_mute
    data:
      is_volume_muted: true
    target:
      entity_id: '{{ playback_entity }}'
  - service: media_player.play_media
    data:
      media_content_id: '{{ media_location }}'
      media_content_type: '{{ media_type }}'
    target:
      entity_id: '{{ playback_entity }}'
  - wait_template: '{% if states(playback_entity) == ''playing'' %}true{% endif %}'
    timeout: '00:00:02'
    continue_on_timeout: true
  - choose:
      - conditions:
          - condition: template
            value_template: '{{ playback_volume is number and playback_volume > -1 }}'
        sequence:
          - service: media_player.volume_set
            data:
              volume_level: ' {{ playback_volume / 100 }} '
            target:
              entity_id: '{{ playback_entity }}'
  - service: media_player.volume_mute
    data:
      is_volume_muted: false
    target:
      entity_id: '{{ playback_entity }}'
  - wait_template: '{% if states(playback_entity) == ''idle'' %}true{% endif %}'
    timeout: '00:05:00'
    continue_on_timeout: false
  - service: scene.turn_on
    data: {}
    target:
      entity_id: scene.before_state_{{ playback_entity|replace(".", "_") }}

@markdavidoff I also don’t see why this would help not getting the cast sound. While testing it myself, I also still get the sound.
Resume of media also does not work by use of scenes with Google Home, becuase of that I have created a script which does work, but which is almost 1000 lines long (also because I try to incorporate all use cases, and it works differently for Spotify, TuneIn, Youtube Music.
Here is a link to my script: Script to resume Google Cast devices after they have been interrupted by any action

I think to not get the cast sound, the approach above in the first post will work best. I do see some room for improvement though, maybe I will look into it in the near future.