This is sent by the server to update the progress of fuel burning or progress of an item being smelted. The smelting bar ranges from 0 to 200, while the max value of the fuel bar depends on the type of fuel used (300 for any wood, 100 for sticks or a sapling, 1600 for coal, and 20000 for a lava bucket.).
Clientbound
Field
Type
Description
Window ID
Byte
The incremental ID of the window. Ranges from 0 to 99
Bar
Short
0 for the smelting bar, 1 for the fuel bar, 2 for max burn time