Systems and methods for signaling downsampling offset information in video coding

A method of decoding video data, the method comprising:

• receiving a phase indication information message;
• parsing a syntax element in the phase indication information message indicating a horizontal phase numerator value;
• parsing a syntax element in the phase indication information message indicating a horizontal phase denominator value;
• determining a horizontal position of luminance sampling locations relative to a rendering window based on the indicated horizontal phase numerator value and the indicated horizontal phase denominator value, wherein the horizontal position of luminance sampling locations relative to a rendering window is equal to a quotient of the indicated horizontal phase numerator value and the indicated horizontal phase denominator value and is expressed in units of a horizontal distance between two horizontally adjacent luma sampling locations;
• parsing a syntax element in the phase indication information message indicating a vertical phase numerator value;
• parsing a syntax element in the phase indication information message indicating a vertical phase denominator value;
• and
• determining a vertical position of luminance sampling locations relative to a display window based on the indicated vertical phase numerator value and the indicated vertical phase denominator value, wherein the vertical position of luminance sampling locations relative to a rendering window is equal to a quotient of the indicated vertical phase numerator value and the indicated vertical phase denominator value and is expressed in units of a vertical distance between two vertically adjacent luma sampling locations,
• wherein the phase indication message applies to a current cropped decoded picture and persists for all subsequent pictures of a current layer in output order with the same cropped picture width and cropped picture height as the current cropped decoded picture until a picture in the current layer with an associated phase indication information message and the same cropped picture width and cropped picture height as the current cropped decoded picture is output and follows the current picture in output order.

A device comprising one or more processors configured to:

• receive a phase indication information message;
• parse a syntax element in the phase indication information message indicating a horizontal phase numerator value;
• parse a syntax element in the phase indication information message indicating a horizontal phase denominator value;
• determine a horizontal position of luminance sampling locations relative to a rendering window based on the indicated horizontal phase numerator value and the indicated horizontal phase denominator value, wherein the horizontal position of luminance sampling locations relative to a rendering window is equal to a quotient of the indicated horizontal phase numerator value and the indicated horizontal phase denominator value and is expressed in units of a horizontal distance between two horizontally adjacent luma sampling locations;
• parse a syntax element in the phase indication information message indicating a vertical phase numerator value;
• parse a syntax element in the phase indication information message indicating a vertical phase denominator value;
• and
• determine a vertical position of luminance sampling locations relative to a display window based on the indicated vertical phase numerator value and the indicated vertical phase denominator value, wherein the vertical position of luminance sampling locations relative to a rendering window is equal to a quotient of the indicated vertical phase numerator value and the indicated vertical phase denominator value and is expressed in units of a vertical distance between two vertically adjacent luma sampling locations,
• wherein the phase indication message applies to a current cropped decoded picture and persists for all subsequent pictures of a current layer in output order with the same cropped picture width and cropped picture height as the current cropped decoded picture until a picture in the current layer with an associated phase indication information message and the same cropped picture width and cropped picture height as the current cropped decoded picture is output and follows the current picture in output order.