The disclosure provides a method of making watermarking data embedded in an Elementary Stream ES accessible to a receiver. The ES comprises video and/or audio data and is to be transmitted as a Packetized Elementary Stream PES in a Transport Stream TS such that the receiver can use the watermarking data to watermark the video and/or audio data in the ES without reconstructing the ES from the TS. The watermarking data identifies one or more watermarking locations in the video and/or audio data in the ES to be modified by the receiver in accordance with the watermarking data. The method comprises determining respective one or more watermarking TS locations in the TS corresponding to the one or more watermarking locations. The method further comprises embedding, in the ES, the watermarking data including watermarking location information identifying the one or more watermarking TS locations, or modifying watermarking data embedded in the ES by adding the watermarking location information. The method may further comprise subsequent to embedding or modifying the watermarking data, packetizing the ES into one or more PES packets, each packet comprising a packet header, and adding watermarking data location information identifying a location in the TS corresponding to a location of the watermarking data in the ES to the packet header of a PES packet (or in a TS header or elsewhere in the TS). The disclosure also provides a corresponding method of watermarking and related systems, devices, computer programs and Transport Streams.