Every time a video or audio volley is sent, it is automatically transcribed. This allows you to turn closed captioning on, as well as to have a transcript of the entire conversation. There is not a way to turn transcripts off, but you can turn off closed captioning if you would like. To navigate to the transcript view of a conversation, click the "Transcript" button in the upper right hand-corner, and the transcript view will open on the right side of your screen. To exit the transcript view, simply tap the transcript button again and it will disappear.
Pro tip: click anywhere in the transcript to be taken to that specific spot of the volley you're listening to!