Question: What happens to the calculated buffer depth value if the result of subtracting the current playout time from the latest playout time of media units in the buffer is negative?
Option 1: The buffer depth is set to a minimum threshold value defined by the protocol.
Option 2: The buffer depth is reported as a negative value to indicate a buffering issue.
Option 3: The calculation is repeated at the start of the next measurement period.
Option 4: The buffer depth shall be set to zero.
Explanation: According to the protocol's handling of buffer depth calculations, if the subtraction yields a negative result (indicating an anomaly in timing), the specification mandates setting the buffer depth to zero. This ensures that unrealistic or non-applicable values are not reported, maintaining the integrity of the buffering metric for streaming services.