An encoding data processing apparatus generates a marked copy of a video material item by embedding a payload data word into the video material item. The video material item includes a plurality of video frames. The encoding data processing apparatus comprises a code word generator, a shuffle processor and an embedding data processor. The code word generator is operable to generate a water mark code word from the payload data word and to read data representing the water mark code word into a shuffle data store. The shuffle processor is operable to generate pseudo randomly at least one address within an address space of the shuffle data store for each of the video frames and to read data representing part or parts of the water mark code word out from the data store at locations identified by the pseudo randomly generated address. The data embedding processor is operable to receive the video material item and to embed the data representing the part or parts of the water mark code word read out from the shuffle data store for each frame into a corresponding frame of the video material item. As such, by randomly embedding different parts of the code word into each frame of the video material item, a likelihood of an attacker being able to identify the code word within the video material item is substantially reduced. Security of the payload data word represented by the water mark code word is therefore improved.