List of fields to return.
To add several fields, separate each value with a comma (i.e. title,description)
Sample of possible values: title,description,id,channel,content_provider,country,created_time,duration,embed_html,embed_url,geoblocking,is_created_for_kids,language,mode,private,private_id,publish_date,published,url
See the exhaustive list of possible values and their description.