This paper presents task 4 of the Detection and Classification of Acoustic Scenes and Events (DCASE) 2019 challenge and provides a first analysis of the challenge results. The task is a follow up to task 4 of DCASE 2018, and involves training systems for large-scale detection of sound events using a combination of weakly labeled data, i.e. training labels without time boundaries, and synthesized strongly-labeled data. The paper focuses in particular on the additional synthetic, strongly labeled, dataset provided this year. More details about the analysis of the results will be provided after the evaluation period (July 2019).