The present disclosure relates to methods and devices for testing video data being rendered at or using a media device. A plurality of video frames to be rendered is received, each frame comprising one or more primary screen objects and at least one further screen object. The received frames are rendered at or using the media device wherein the at least one further screen object is superimposed on the one or more primary screen objects of a given frame during rendering. The rendered frames are provided to a data model. Extracted metadata indicating the presence or absence of further screen objects in the rendered video frames is the output of the data model. The data model is also provided with original metadata associated with the video frames prior to rendering. The rendering of each further screen object is then tested based on the original metadata and extracted metadata relating to a given video frame. The disclosure also extends to associated methods and devices for generating training data for testing rendering of video frame and training a data model using the training data.