Help me to spliting a large OSM file into small pieces...

I am using this video to get 3d building from a openstreetmap:

It works great but the software does not work with large osm files… like a complete city.

Can you give me instructions to achieve my goal?

If you have other idea to get my goal I will really appreciate…

thank you

Use osmconvert with a bbox or polygon filter.

There is also a splitter program associated with mkgmap which will write out one osm file into several. Lastly osmosis can also process files into multiple files, but it can be a little more complicated to get working.