Olleggerr

Understood. Thanks a lot for help!

Here is mine example. And .mca file too. Executable and region file: https://yadi.sk/d/wXBFG0M33LGxV2 Code: https://pastebin.com/ePMUhfhv

I am talking about this padding. You described me 2048 bytes of additional data after compressed chunk's NBT data. But i still have data which meaning i cant understand. 758 bytes before 00 bytes of padding and after Nibble data.

That is great but i still have 758 bytes of unknown data in padding (excluding compressed NBT data, header, 4-bit nibble and 00 padding). Do you have any idea of what is it?

So 4-bit nibble's length is always 2048 bytes, right? And it placed just after main NBT data?

When i was trying to create compressing tool for minecraft worlds and starts trying to extract chunks' NBT data I found that "padding to be a multiple of 4096B" which should be filled with zeroes is filled with some data. I found this data only in Forge world saves. Does Minecraft Forge save some data in region (.mca) files? If it is, what is this data is, like is this NBT or compressed NBT or other type of data? Hope you will understand me. Thanks in advance!