Audio Play (MP3 or Wav file) with I2s MAX98357A codec

Hi,

I'm using nRF52840 DK with ncs V 2.6.0. I plan to create an mp3 or WAV audio player. I tried using the MAX98357A with the i2s nRF52840 DK board, building a project i2s example, and feeding converted sound data into a 16-bit array. The audio isn't clear. Can you help me how to play a wav or mp3 file using the MAX93857A codec? for file storing I am using external spi flash also required 
How can I configure the file system for Flash and need to read files from external flash and play audio files?

Thanks,

Parth