Videos freezing in high quality mode on mac

hello, i hv upgraded my MacBook pro's ram to 8GB, but still rekordbox video is not   playing videos in high quality mode. my MacBook pro's system configuration is

  Model Name: MacBook Pro

  Model Identifier: MacBookPro9,2

  Processor Name: Intel Core i5

  Processor Speed: 2.5 GHz

  Number of Processors: 1

  Total Number of Cores: 2

  L2 Cache (per Core): 256 KB

  L3 Cache: 3 MB

  Memory: 8 GB