A video standard essentially defines a set of methods for compressing video - it's up to the encoding applications to decide how to apply those methods and wher

A video standard essentially defines a set of methods for compressing video - it's up to the encoding applications to decide how to apply those methods and where. Basically, the smarter decisions the encoder can make, the higher quality results it will produce. This is why all H.264 encoders are not created equal. As an example of "techniques" that can be applied to compressing videos, one of the reasons why x264 is considered the best H.264 encoder out there is due to its advanced psychovisual optimizations - these are basically methods that will increase the perceived visual quality for human viewers, but decreases the quality in the eyes of metrics like PSNR and SSIM.