Obviousness

Analysis of Obviousness for U.S. Patent No. 8,942,252 B2

I. Introduction

Under 35 U.S.C. § 103, a patent claim is considered obvious if the differences between the claimed invention and the prior art are such that the subject matter as a whole would have been obvious at the time the invention was made to a person having ordinary skill in the art (PHOSITA). This analysis examines the claims of U.S. Patent No. 8,942,252 B2 in light of prior art available before its priority date of December 17, 2001.

The core of the '252 patent is a master/slave system for synchronizing multimedia playback across different rendering devices. The master device sends its "rendering time" (playback position) and "device time" (local clock time) to slave devices. The slave devices then calculate the time difference and adjust their playback to maintain synchronization. A key aspect highlighted in the claims is the "smoothing" of this time differential to avoid abrupt playback adjustments.

II. Prior Art References

A combination of prior art references teaches the fundamental concepts of the '252 patent, suggesting that its claims would have been obvious to a person of ordinary skill in the art.

• European Patent Application EP0550197A2 ("Koval"): Published well before the '252 patent's priority date, Koval discloses a multimedia data processing system that uses a master/slave relationship to synchronize multiple data streams. Koval explicitly describes one stream being designated as the "master" and others as "slaves." The master stream generates "sync pulses" that contain a clock value, and a slave receives these pulses to determine if it is out-of-sync. Koval also teaches "adaptive resynchronization" to speed up or slow down a slave stream. This directly corresponds to the core master/slave architecture and playback adjustment mechanism of the '252 patent.

• Network Time Protocol (NTP): As a long-established standard for synchronizing clocks over a computer network, NTP was well within the knowledge of a PHOSITA before 2001. NTP provides the fundamental mechanism for devices to compare their local clocks and calculate offsets, which is analogous to the '252 patent's concept of comparing "device times." The use of timestamps in NTP to account for network latency is a standard technique that a skilled artisan would have readily understood and applied to a multimedia synchronization problem.

• General Principles of Signal Processing and Control Systems: The concept of "smoothing" a differential to prevent jarring corrections is a fundamental principle in control systems and signal processing. A person of ordinary skill in the art of multimedia systems would have been familiar with techniques like averaging, weighted averaging, or using decaying functions to smooth out variations in data. These are standard methods to ensure gradual and less perceptible adjustments in a system, which would have been directly applicable to the problem of synchronizing media playback without causing noticeable skips or stalls.

III. Obviousness Argument

A person of ordinary skill in the art, faced with the problem of synchronizing multimedia playback across networked devices with independent clocks, would have found it obvious to combine the teachings of Koval, the principles of NTP, and standard signal processing techniques to arrive at the invention claimed in the '252 patent.

Claim 1 (Master Device Method):

1. "A master rendering device rendering a first content stream": Koval directly teaches a "master stream" that outputs data to a multimedia device.
2. "sending, from the master rendering device to a first one of a plurality of slave devices, a plurality of master rendering times indicative of statuses of the rendering the first content stream": Koval's master stream generates and sends "sync pulses" with a clock value representing the time the master stream started. A PHOSITA would have understood that sending a plurality of these pulses over time provides ongoing status of the rendering.
3. "wherein the first slave device is configured to smooth a rendering time differential": While Koval doesn't explicitly use the term "smooth," it teaches "adaptive resynchronization" to speed up or slow down a slave stream. A PHOSITA would have recognized that implementing such an adaptation in a way that is not jarring to the user would require smoothing the calculated time difference. This would be a routine implementation detail to avoid abrupt changes in playback, drawing on common knowledge in signal processing and control theory. The motivation to smooth the correction is inherent in the goal of providing a pleasant, uninterrupted user experience, a fundamental objective in multimedia system design.

Claim 11 (Slave Device Method):

1. "receiving, at a slave device, a particular content stream": Koval's system includes "slave streams" that receive data for output.
2. "receiving, at the slave device from a master rendering device, a plurality of master rendering times": This is the slave-side equivalent of the master sending sync pulses in Koval.
3. "the slave device determining a smoothed rendering time differential that exists between the master rendering device and the slave device, wherein the determining is based on calculations using the plurality of master rendering times and a plurality of slave rendering times": Koval describes the slave comparing its time with the master's time to determine if it is "out-of-sync." The motivation to combine this with NTP-like clock synchronization principles to account for different device clocks would have been strong. As with claim 1, the step of "smoothing" this differential by using a plurality of timing messages (both master and slave) is an obvious improvement to prevent abrupt playback adjustments. A skilled artisan would have naturally applied averaging or other filtering techniques to the calculated time differences to achieve a smooth correction, which is a predictable solution to a known problem in control systems.
4. "based on the smoothed rendering time differential, the slave device rendering the particular content stream synchronously with the master rendering device": This is the explicit goal and outcome of Koval's "adaptive resynchronization."

IV. Motivation to Combine

The motivation to combine these prior art elements is straightforward. A developer creating a synchronized multimedia system based on Koval's master/slave architecture would inevitably encounter the problem of clock drift between devices, a well-known issue addressed by protocols like NTP. It would have been an obvious step to incorporate NTP-like clock synchronization to get a more accurate comparison of device times.

Furthermore, upon implementing the "adaptive resynchronization" taught by Koval, the problem of abrupt, jarring playback corrections would immediately become apparent. A person of ordinary skill in the art would have been motivated to solve this by applying standard smoothing algorithms from the field of signal processing and control systems to the calculated time differential. This would be a predictable solution to a well-understood problem in the field.

V. Conclusion

The independent claims of US8942252B2 recite a combination of elements that were well-known in the prior art before the patent's priority date. The master/slave architecture for synchronization was taught by Koval. The method for synchronizing device clocks was established by NTP. The technique of smoothing a corrective signal to avoid abrupt changes is a fundamental concept in engineering. A person having ordinary skill in the art of multimedia systems would have been motivated to combine these known elements to create the system described in the '252 patent to achieve a smoothly synchronized multimedia experience. Therefore, the claims of US8942252B2 are rendered obvious under 35 U.S.C. § 103.