Couldn't change a frame rate

This issue relates to #7 

I tried your advise and updated 
https://github.com/dbof10/Bitmp4/blob/master/lib-bitmp4/src/main/java/com/ctech/bitmp4/MP4Encoder.java#L64

but it didn't really affect the output.
Is there any other line of code I need to update to change a frame rate?