These metrics explore the decoded images looking for distortions (blockiness, blur, etc.) but they also extract several information from the bitstream, like the location of the badly reconstructed blocks (due to lost or corrupted video packets). That's why hybrid metrics combine the best of the two worlds, enabling to increase again the precision of the computed quality scores.
These hybrid metrics are specially interesting when measuring the impact of transmission errors on perceived video quality.
For each codec, the corresponding metric measures the distortions generated by the encoding:
Related product: Video Quality Monitor (VQM) (ask for a free evaluation version).