I just found the solution for the problem. You need to set the variable and parse it as json like the following example:
{% set conversion_assets = {"type":"FORM","id":module.form.form_id,"position":"PRE"} %}
{% video_player "embed_player"
overrideable=False
type={{ module.video.player_type || 'scriptV4' }}
full_width={{ module.video.size_type == 'auto_full_width' }}
hide_playlist=True
viral_sharing=False
embed_button=False
auto_play=True
width='1920', height='1080'
player_id={{ item.video }}
conversion_asset={{ conversion_assets|tojson|safe }}
%}