Chunking Blob Array to smaller Blob Arryas!

Is there any way to chunk Blob Array of size 2mb to smaller Blob Arrays of size 500kb each ?
For say :

public func VideoChunk(chunkId : Nat , chunkData : [Blob]){
 //I need to chunk this chunkData into 4 parts lets say , How can I do that?

Also , Finally after chunking it in smaller size , I need to put these chunks into a Trie Data Structure.
So , What would be better in Time Complexity Wise?
Putting Complete Blob Array of size 2mb into Trie , or putting 4 Chunks of 500kb one by one in Trie ?
(If Chunking in 500kb is better then Why and how to do it , If you have any idea?)

Thanks in Advance!