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EP-4198973-B1 - WATERMARKING USING STARTING PHASE MODULATION

EP4198973B1EP 4198973 B1EP4198973 B1EP 4198973B1EP-4198973-B1

Inventors

  • TOPCHY, ALEXANDER
  • KUZNETSOV, VLADIMIR
  • DAVIS, Jeremey M.

Dates

Publication Date
20260506
Application Date
20191216

Claims (11)

  1. A method for watermark decoding comprising: determining a first analyzed phase value for a first watermark component of a watermarked media signal (108) at a first time; the method is characterised by further comprising: determining a second analyzed phase value for a second watermark component of the watermarked media signal (108) at the first time; determining whether a sum of differences for the first and second analyzed phase values with respect to a first one of a plurality of possible starting phase values satisfies a difference threshold; if it is determined that the sum of differences satisfies the difference threshold: decoding a first bit value corresponding to the first one of the possible starting phase values, and determining a watermark payload based on the first bit value, the watermark payload including a watermark symbol and/or auxiliary information; and if it is determined that the sum of differences does not satisfy the difference threshold: determining whether a second sum of differences for the analyzed phase values relative to a second one of the possible starting phase values satisfies the difference threshold, the analyzed phase values including the first analyzed phase value and the second analyzed phase value; and if it is determined that the second sum of differences satisfies the difference threshold: decoding a second bit value corresponding to the second one of the possible starting phase values, and determining the watermark payload based on the second bit value.
  2. The method of claim 1, wherein in response to determining that the sum of differences and the second sum of differences do not satisfy the difference threshold: determining a third analyzed phase value of the first watermark component at a second time, the second time prior to the first time; and determining a fourth analyzed phase value of the second watermark component at the second time.
  3. The method of claim 2, further including: determining a third sum of differences for the third analyzed phase value and the fourth analyzed phase value relative to the first one of the possible starting phase values; determining a fourth sum of differences for the third analyzed phase value and the fourth analyzed phase value relative to the second one of the possible starting phase values; and in response to one of the third sum of differences or the fourth sum of differences satisfying the difference threshold, selecting a corresponding one of the first one of the possible starting phase values or the second one of the possible starting phase values to be a starting phase value.
  4. The method of claim 1, further including: iteratively determining additional analyzed phase values of the first and second watermark components; and iteratively determining additional sums of differences of the additional analyzed phase values relative to the first one of the possible starting phase values and the second one of the possible starting phase values until one of the additional sums of differences satisfies the difference threshold.
  5. The method of claim 1, further including: iteratively determining additional analyzed phase values of the first and second watermark components; and iteratively determining additional sums of differences of the additional analyzed phase values relative to the first one of the possible starting phase values and the second one of the possible starting phase values until a symbol duration is reached.
  6. The method of any one of claims 1 to 5, further including selecting the first and second watermark components based on a signal strength of the first and second watermark components, and wherein the sum of differences is determined in such a way as to account for phase wrapping.
  7. A watermark decoding apparatus (116) comprising: memory (1014, 1016; 1114, 1116); instructions (400; 500; 1032); and processor circuitry (1012; 1112) arranged to execute the instructions (400; 500; 1032) to at least: determine a first analyzed phase value for a first watermark component of a watermarked media signal (108) at a first time; determine a second analyzed phase value for a second watermark component of the watermarked media signal (108) at a first time; determine whether a sum of differences for the first and second analyzed phase values with respect to a first one of a plurality of possible starting phase values satisfies a difference threshold; if it is determined that the sum of differences satisfies the difference threshold: decode a first bit value corresponding to the first one of the possible starting phase values, and determine a watermark payload based on the first bit value, the watermark payload including a symbol and/or auxiliary information; and if it is determined that the sum of differences does not satisfy the difference threshold: determine whether a second sum of differences for the analyzed phase values relative to a second one of the possible starting phase values satisfies the difference threshold, the analyzed phase values including the first analyzed phase value and the second analyzed phase value; and if it is determined that the second sum of differences satisfies the difference threshold: decode a second bit value corresponding to the second one of the possible starting phase values, and determine the watermark payload based on the second bit value.
  8. The apparatus of claim 7, wherein the processor circuitry (1012; 1112) is arranged to further: in response to determining that the sum of differences and the second sum of differences do not satisfy the difference threshold: determine a third analyzed phase value of the first watermark component at a second time, the second time prior to the first time; and determine a fourth analyzed phase value of the second watermark component at the second time.
  9. The apparatus of claim 8, wherein the processor circuitry (1012; 1112) is arranged to further: determine a third sum of differences for a third analyzed phase value and a fourth analyzed phase value relative to the first one of the possible starting phase values; determine a fourth sum of differences for the third analyzed phase value and the fourth analyzed phase value relative to the second one of the possible starting phase values; and in response to one of the third sum of differences or the fourth sum of differences satisfying the difference threshold, select a corresponding one of the first one of the possible starting phase values or the second one of the possible starting phase values to be a starting phase value.
  10. The apparatus of claim 7, wherein the processor circuitry (1012; 1112) is arranged to further: iteratively determine additional analyzed phase values of the first and second watermark components; and iteratively determine additional sums of differences of the additional analyzed phase values relative to the first one of the possible starting phase values and the second one of the possible starting phase values until one of the additional sums of differences satisfies the difference threshold.
  11. At least one machine-readable medium comprising machine-readable instructions to implement the method of any one of claims 1 to 6.

Description

FIELD OF THE DISCLOSURE This disclosure relates generally to media monitoring, and, more particularly, to apparatus and methods for watermarking using starting phase modulation. BACKGROUND Media, such as a television broadcast, may be encoded with watermarks that, when detected, are decoded to identify the media that was presented. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of an example environment for watermarking using starting phase modulation.FIG. 2 is a block diagram of the example watermark encoder of FIG. 1 to encode watermarks using starting phase modulation in accordance with the teachings of this disclosure.FIG. 3 is a block diagram of the example watermark decoder of FIG. 1 to decode watermarks encoded utilizing starting phase modulation in accordance with the teachings of this disclosure.FIG. 4 is a flowchart representative of machine readable instructions that may be executed to implement the watermark encoder of FIGS. 1 and 2 to encode media signals with watermarks using starting phase modulation.FIGS. 5A-5B are a flowchart representative of machine readable instructions that may be executed to implement the watermark decoder of FIGS. 1 and 3 to decode watermarks encoded using starting phase modulation.FIG. 6 is example code for implementing the watermark decoding process described in connection with FIGS. 5A-5B.FIG. 7 is a schematic illustrating multiple watermark components having different frequencies but a common starting phase value.FIG. 8 is an example phase plot of a plurality of watermark components having a common starting phase value.FIG. 9 is an example phase distribution plot illustrating convergence of numerical methods to determine watermark starting phase as described herein.FIG. 10 is a block diagram of an example processor platform structured to execute the example machine readable instructions of FIG. 4 to implement the example watermark encoder of FIGS. 1-2.FIG. 11 is a block diagram of an example processor platform structured to execute the example machine readable instructions of FIGS. 5A-5B to implement the example watermark decoder of FIGS. 1 and 3.The figures are not to scale. In general, the same reference numbers will be used throughout the drawing(s) and accompanying written description to refer to the same or like parts. DETAILED DESCRIPTION Audience measurement entities desire knowledge on how users interact with media devices such as smartphones, tablets, laptops, smart televisions, etc. In particular, media monitoring companies want to monitor media presentations made at the media devices to, among other things, monitor exposure to advertisements, determine advertisement effectiveness, determine user behavior, identify purchasing behavior associated with various demographics, etc. Watermarking is a technique used to identify media such as television broadcasts, radio broadcasts, advertisements (television and/or radio), downloaded media, streaming media, prepackaged media, etc. Existing watermarking techniques identify media by embedding one or more codes (e.g., one or more watermarks), such as media identifying information and/or an identifier that may be mapped to media identifying information, into an audio and/or video component. In some examples, the audio or video component is selected to have a signal characteristic sufficient to hide the watermark. As used herein, the terms "code" or "watermark" are used interchangeably and are defined to mean any identification information (e.g., an identifier) that may be inserted or embedded in the audio or video of media (e.g., a program or advertisement) for the purpose of identifying the media or for another purpose such as tuning (e.g., a packet identifying header). As used herein "media" refers to audio and/or visual (still or moving) content and/or advertisements. To identify watermarked media, the watermark(s) are extracted and used to access a table of reference watermarks that are mapped to media identifying information. Watermarks are encoded into media signals by selecting audio frequency ranges that have may have minimal influence on a user's perception of the media signal (e.g., as determined empirically via psychoacoustics) and modifying the media signal in this frequency range. Watermarks typically include a plurality of watermark components (e.g., symbols, tones, etc.). The watermark components are embedded in the media signal in a manner that is ideally imperceptible to a listener, but discernable when audio characteristics are analyzed during watermark decoding. One approach to audio watermarking is based on embedding short tones (e.g., sine waves) of particular frequencies and amplitudes, where the choice of tones is modulated by the watermark information payload. Specific tone frequency ranges and/or tone amplitude values can be associated with different values of watermark components. For example, an amplitude value satisfying a threshold may be observed at a tone frequency where