You're seeing just the callback
handle_prepared_to_playing, go back to Membrane.Element.Base module for more information.
handle_prepared_to_playing( context :: Membrane.Element.CallbackContext.PlaybackChange.t(), state :: Membrane.Element.state_t() ) :: callback_return_t()
Callback invoked when element is supposed to start playing (goes from state
This is moment when initial demands are sent and first buffers are generated if there are any pads in the push mode.