Using finer quantizer for keyframes

Metrics on video-1-short:
           RATE (%)  DSNR (dB)
    PSNR -0.20639  0.01102
 PSNRHVS -0.16628  0.01316
    SSIM -0.20454  0.00984
FASTSSIM -0.22283  0.01366
Adds optional code to measure the actual overhead of the entropy coder