I am working an OpenMAX-IL video decoder and have looked at the example code (MPEG2 decoder) and the conformance test code. I noticed that both of these allow the app to modify the OMX_IndexParamVideoPortFormat data using the SetParameter method.

I don't understand what this is used for. From the example code, I can see that the codec can provide a number of different port settings (e.g. different raw data formats on an output port), but why would the app overwrite these?

Any help appreciated.