FindProducer
static BMidiProducer *FindProducer(int32 id, bool localOnly = false);
BMidiProducer* endpoint = BMidiRoster::FindProducer(fInputId);
endpoint = BMidiRoster::FindProducer(fInputId);
BMidiProducer* producer = roster->FindProducer(producerID);
BMidiProducer* producer = roster->FindProducer(fProducerID);