// work out buffer requirements, check port is in the right state
   error = OMX_GetParameter(comp->comp, OMX_IndexParamPortDefinition, &portdef);
   if(error != OMX_ErrorNone || portdef.bEnabled != OMX_FALSE || portdef.nBufferCountActual == 0 || portdef.nBufferSize == 0)
      return -1;

   portdef.nBufferSize /= 80;
   portdef.nBufferCountActual = 20;
   error = OMX_SetParameter(comp->comp, OMX_IndexParamPortDefinition, &portdef);
   if (error != OMX_ErrorNone) {
       printf ("Error %d" , error);
       return -1;
   }
   printf ("buffsize: %d %d\n", portdef.nBufferSize, portdef.nBufferCountActual);
   error = OMX_GetParameter(comp->comp, OMX_IndexParamPortDefinition, &portdef);
   if(error != OMX_ErrorNone || portdef.bEnabled != OMX_FALSE || portdef.nBufferCountActual == 0 || portdef.nBufferSize == 0)
      return -1;
   printf ("buffsize: %d %d\n", portdef.nBufferSize, portdef.nBufferCountActual);