CN-122001508-A - Clock drift indicating internal clock in sensor device

CN122001508ACN 122001508 ACN122001508 ACN 122001508ACN-122001508-A

Abstract

A clock drift indicative of an internal clock in a sensor device is provided. A method for indicating clock drift of an internal clock included in a sensor device, the method comprising capturing (S302) a first data frame by the sensor device, associating (S304) the first data frame with a first point in time by the sensor device, the first point in time indicating a point in time of the internal clock when the first data frame was captured, receiving (S306) time synchronization data by the sensor device via a network protocol for clock synchronization, determining (S308) a reference point in time by the sensor device, the reference point in time indicating a point in time of the reference clock when the first data frame was captured, determining (S310) an offset between the first point in time and the reference point in time by the sensor device, and associating (S312) the first data frame with data indicating the offset by the sensor device when the offset exceeds a threshold offset.

Inventors

Andrea Banquo
CHRISTIAN STORM

Assignees

安讯士有限公司

Dates

Publication Date: 20260508
Application Date: 20251031
Priority Date: 20241106

Claims (15)

1. A method for indicating clock drift of an internal clock included in a sensor device, the method comprising: capturing, by the sensor device, a first data frame; Associating, by the sensor device, the first data frame with a first point in time indicating a point in time of the internal clock when the first data frame was captured; receiving, by the sensor device, time synchronization data via a network protocol for clock synchronization; Determining, by the sensor device, a reference point in time using the time synchronization data, the reference point in time indicating a point in time of a reference clock when the first data frame was captured; determining an offset between the first point in time and the reference point in time by the sensor device, and When the offset exceeds a threshold offset, the first data frame is associated with data indicative of the offset by the sensor device.
2. The method of claim 1, wherein the sensor device is a webcam, wherein the first data frame is a first image frame, and wherein associating, by the webcam, the first image frame with data indicative of the offset comprises: graphic data that visualizes the data indicative of the offset is added to an overlay associated with the first image frame.
3. The method of claim 1, wherein associating, by the sensor device, the first data frame with data indicative of the offset comprises adding the data indicative of the offset as first metadata associated with the first data frame.
4. A method according to claim 3, wherein the first metadata associated with the first data frame is provided as at least one of: Data stream metadata, metadata added to the header of the first data frame, and a separate metadata stream.
5. A method according to claim 3, further comprising: Determining a signature using the first metadata and sensor data of the first data frame, and The signature is integrated into a record comprising the first data frame and the first metadata.
6. The method of claim 1, wherein associating, by the sensor device, the first data frame with the first point in time comprises: the first point in time is added as second metadata associated with the first data frame.
7. The method of claim 1, wherein the sensor device is a webcam, wherein the first data frame is a first image frame, and wherein associating, by the webcam, the first image frame with the first point in time comprises: Graphics data visualizing the first point in time is added to an overlay associated with the first image frame.
8. The method of claim 1, further comprising: Continuously capturing data frames by the sensor device; for each captured data frame, associating, by the sensor device, the captured data frame with another point in time indicative of a point in time of the internal clock when the captured data frame was captured; at predetermined intervals while continuously capturing the data frames: receiving, by the sensor device, time synchronization data via the network protocol for clock synchronization; determining, by the sensor device, another reference point in time using the time synchronization data, the another reference point in time indicating a point in time of the reference clock when a newly captured data frame was captured; Determining a further offset between the further point in time associated with the most recently captured image frame and the further reference point in time; When the further offset exceeds a threshold offset, the newly captured data frame is associated by the sensor device with data indicative of the further offset.
9. The method of claim 1, further comprising: the internal clock is adjusted to reduce the offset, wherein the size of the adjustment is limited by specifications of the network protocol used for clock synchronization.
10. The method of claim 1, further comprising: at a device separate from the sensor device, the first point in time and the data indicative of the offset are used to determine an accurate point in time to capture the first data frame.
11. The method of claim 10, further comprising: At the device separate from the sensor device, the exact point in time to capture the second data frame is determined using: a second point in time associated with the second data frame, the second point in time indicating a point in time of the internal clock of the sensor device when the second data frame was captured, and The data indicating the offset associated with the first data frame.
12. A non-transitory computer readable storage medium having instructions stored thereon for implementing the method of any of claims 1 to 11 when executed on one or more devices having processing capabilities.
13. A sensor device configured to indicate clock drift of an internal clock included in the sensor device, the sensor device configured to: Capturing a first data frame; Associating the first data frame with a first point in time, the first point in time indicating a point in time of the internal clock when the first data frame was captured; receiving time synchronization data via a network protocol for clock synchronization; determining a reference point in time using the time synchronization data, the reference point in time indicating a point in time of a reference clock when the first data frame was captured; determining an offset between the first point in time and the reference point in time, and When the offset exceeds a threshold offset, the first data frame is associated with data indicative of the offset.
14. A system comprising the sensor device of claim 13 and a device separate from the sensor device, the device separate from the sensor device configured to: An accurate point in time for capturing the first data frame by the sensor device is determined using the first point in time and the data indicative of the offset.
15. The system of claim 14, wherein the device separate from the sensor device is further configured to: the exact point in time at which the second data frame was captured by the sensor device is determined using: a second point in time associated with the second data frame, the second point in time indicating a point in time of the internal clock of the sensor device when the second data frame was captured, and The data indicating the offset associated with the first data frame.

Description

Clock drift indicating internal clock in sensor device Technical Field The present invention relates to networking systems and time synchronization protocols, and in particular, to methods, devices, and systems for indicating clock drift of an internal clock in a sensor device. Background In modern networking environments, sensor devices such as cameras and microphones, as well as other network-based sensor devices, rely heavily on accurate timing to ensure synchronous operation. These devices typically utilize a network protocol for clock synchronization, which allows them to periodically adjust their internal clocks to match a central time reference (CENTRAL TIME REFERENCE). Such synchronization is critical for applications that depend on accurate time stamping, such as video surveillance and event surveillance. One widely used protocol for clock synchronization is the Network Time Protocol (NTP). NTP enables the device to periodically adjust its clock frequency to gradually coincide with the time of the NTP server, thereby ensuring that the internal clock time remains accurate over time (i.e., achieving the same time value and average time lapse rate as the NTP server (AVERAGE TIME-TICKING SPEED)). NTP and other similar protocols typically have specific rules on how a device adjusts its clock quickly after detecting a discrepancy to avoid abrupt time drift. For example, when devices connect to a synchronization server, they may employ mechanisms such as slew adjustment (slew adjustment) to make small adjustments to their internal clocks periodically, where the clocks are gradually corrected over time to stay consistent with the time of the server. This can cause problems when the device temporarily loses connection with the synchronization server (which can be caused by network problems, server downtime, or other disruption). During this offline period, the internal clock of the sensor device may begin to deviate from the correct time provided by the server. This drift may occur if the Real Time Clock (RTC) of the sensor fails, resulting in its loss of precision or accuracy over time. This problem is particularly problematic in applications where accurate time alignment is critical, such as video surveillance. For example, in a multi-camera setting, if one or more cameras experience clock drift during a period of disconnection from the synchronization server, their clocks may continue to exhibit different times even after reconnection. Thus, improvements are needed in this regard. Disclosure of Invention In view of the above, it would be advantageous to solve or at least reduce one or several of the drawbacks discussed above, as set forth in the appended independent patent claims. According to a first aspect of the present disclosure there is provided a method for indicating clock drift of an internal clock included in a sensor device, the method comprising capturing, by the sensor device, a first data frame, associating, by the sensor device, the first data frame with a first point in time indicating a point in time of the internal clock when the first data frame was captured, receiving, by the sensor device, time synchronization data via a network protocol for clock synchronization, determining, by the sensor device, a reference point in time using the time synchronization data, the reference point in time indicating a point in time of the reference clock when the first data frame was captured, determining, by the sensor device, an offset between the first point in time and the reference point in time, and associating, by the sensor device, the first data frame with data indicating the offset when the offset exceeds a threshold offset. The present disclosure provides several advantages in indicating clock drift of an internal clock in a sensor device. For example, using the techniques described herein, recording clock drift information and correlating it with sensor data is facilitated when the drift exceeds a predefined threshold (e.g., 0.5 seconds, 1 second, 2 seconds, 3 seconds, 6 seconds, etc.). This ensures that a system implementing the techniques described herein maintains a perception of any significant temporal differences, which may later be used to reconstruct the actual time of a data frame, e.g., for event detection. Thus, such recorded drift information may be used when synchronizing sensor data and/or events detected therein between different sensor devices, wherein clock drift may be different. By accessing this drift data, operators, analysis systems, and post-processing tools (such as those used by law enforcement or security agencies) can adjust for time differences and align events across multiple sensor devices, thereby ensuring accurate time-based event reconstruction. Furthermore, using the techniques described herein, data processing may be improved by avoiding the inclusion of unnecessary drift information when the drift is minimal and below a threshold. If the drift is small a