At high bit rates, the reconstruction error of compressed video is generally proportional to the squared value of quantization step size, such that full quantization step size increments at high bit rates can lead to significant change in the reconstruction error and/or bit rate of the compressed video....http://www.google.com.au/patents/US20050238096?utm_source=gb-gplus-sharePatent US20050238096 - Fractional quantization step sizes for high bit rates
