The part parameter specifies the caption resource parts that the API response will include. Set the parameter value to snippet.

ID of the Google+ Page for the channel that the request is be on behalf of

Note: This parameter is intended exclusively for YouTube content partners. The onBehalfOfContentOwner parameter indicates that the request's authorization credentials identify a YouTube CMS user who is acting on behalf of the content owner specified in the parameter value. This parameter is intended for YouTube content partners that own and manage many different YouTube channels. It allows content owners to authenticate once and get access to all their video and channel data, without having to provide authentication credentials for each individual channel. The actual CMS account that the user authenticates with must be linked to the specified YouTube content owner.

Extra parameter to allow automatically syncing the uploaded caption/transcript with the audio.