A method for data display, comprising: storing an identification code; receiving encoded video content for playback by a video playback device; and decoding the encoded video content so as to output a series of video frames overlaid on a background layer generated by the video playback device while modulating a level of said background layer of the video frames in the series according to the identification code, wherein modulating the background level comprises generating a background having an overall level that is time modulated according to the identification code, and summing the background with the decoded video content, wherein: modulating the background level comprises modifying a color of the background; the background level is defined by a luminance coordinate and two chrominance coordinates, and wherein modifying the color comprises modulating the two chrominance coordinates; modulating the two chrominance coordinates comprises encoding the identification code using an alphabet comprising four symbols mapped over the two chrominance coordinates; and characterised in that: modulating the two chrominance coordinates comprises applying the modulation in a chrominance coordinate system where the chrominance axes are rotated so as to diminish a visual effect of the modulation. storing an identification code; receiving encoded video content for playback by a video playback device; and decoding the encoded video content so as to output a series of video frames overlaid on a background layer generated by the video playback device while modulating a level of said background layer of the video frames in the series according to the identification code, wherein modulating the background level comprises generating a background having an overall level that is time modulated according to the identification code, and summing the background with the decoded video content, wherein: modulating the background level comprises modifying a color of the background; the background level is defined by a luminance coordinate and two chrominance coordinates, and wherein modifying the color comprises modulating the two chrominance coordinates; modulating the two chrominance coordinates comprises encoding the identification code using an alphabet comprising four symbols mapped over the two chrominance coordinates; and characterised in that: modulating the two chrominance coordinates comprises applying the modulation in a chrominance coordinate system where the chrominance axes are rotated so as to diminish a visual effect of the modulation. modulating the background level comprises modifying a color of the background; the background level is defined by a luminance coordinate and two chrominance coordinates, and wherein modifying the color comprises modulating the two chrominance coordinates; modulating the two chrominance coordinates comprises encoding the identification code using an alphabet comprising four symbols mapped over the two chrominance coordinates; and characterised in that: modulating the two chrominance coordinates comprises applying the modulation in a chrominance coordinate system where the chrominance axes are rotated so as to diminish a visual effect of the modulation. modulating the two chrominance coordinates comprises applying the modulation in a chrominance coordinate system where the chrominance axes are rotated so as to diminish a visual effect of the modulation.