PSNR is to this day the most common metric used to measure video quality, despite having been shown for decades to do so with very limited accuracy. Better metrics have been standardised, but their implementations are proprietary and expensive to license, which means that they are unavailable to most researchers. The primary goal of this master's thesis is to develop an implementation of a standardised video quality metric that performs significantly better than PSNR, and make it available as Free Software. Subsequently, we want to provide useful abstractions to make it easy for researchers to implement their own metrics within the framework of this software. An introduction to video quality measurement and its history is presented together with an examination of existing metrics that may be used as foundation for our implementation. We show how the metric called PEVQ standardised in ITU-T Recommendation J.247 is chosen as a basis from which we derive our own metric called OPVQ. The differences between the base and the derived metric are described in detail before we evaluate the performance of OPVQ. OPVQ is implemented, not as a stand-alone program, but as part of a more general toolkit that is called OpenVQ. We explain the considerations that went into the design of this software, and describe the implementation in detail. We also give an introduction to how to use the program, both to assess video quality and to implement a video quality metric.