This is the groupspawn packet which is able to spawn many objets in 1 Packet
before the 3019 (GroupSpawnData) is the 3017 (GroupSpawnStart) which tells the client how much objects are in the Data. You have to parse every entry of object like the single spawn but you have to know that there could be different types : Char, Mob, COS, NPC or Gates.
[3017] //GroupSpawnStart
01 - GroupSpawnType (1 = Spawn, 2 = Despawn)
01 00 - GroupSpawnAmount
[3019] //GroupSpawnData
00 00 00 00 - ObjectID
00 00 .. - data for the objects
[3018] //GroupSpawn End
//Empty
You only have to know which object type comes in because they all are parsed in a different way so you have to check the objectID which is actually the ID in the text files.