Constant libmpv_sys::mpv_error_MPV_ERROR_EVENT_QUEUE_FULL

pub const mpv_error_MPV_ERROR_EVENT_QUEUE_FULL: mpv_error = -1;

The event ringbuffer is full. This means the client is choked, and can't receive any events. This can happen when too many asynchronous requests have been made, but not answered. Probably never happens in practice, unless the mpv core is frozen for some reason, and the client keeps making asynchronous requests. (Bugs in the client API implementation could also trigger this, e.g. if events become "lost".)