iqa makes it difficult to support multiple metrics
Submitted by LRN
This was discussed on the IRC, the gist is that iqa hardcodes all input to be converted to RGB for dssim, and not all metrics can be computed on RGB.
One possible fix is to make existing Iqa class a dssim-only class (renaming it to IqaDssim), and implement other metrics as separate IqaSomething classes. Not a lot of code duplication, since GstVideoAggregator does most of the plumbing anyway.