while for my particular use-case this has always worked with only "stdio recvfd", sio_open(3) mentions that if no further sio_open calls are made all pledges can be dropped except for "audio", so let's keep it.

now player_playnext has enough information to decide wheter to call player_senderr or player_sendeof.

now it includes all the params, not only the rate

there's a small window of time where we could deliver a pause message and crash the player.