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An Apple patent (number 8239748) for a synchronization manager synchronizes multiple media streams. has appeared at the U.S. Patent & Trademark Office. It relates to synchronization of media streams, and more specifically to utilizing clocks on multiple media devices and on a single host to synchronize multiple media streams.
The synchronization manager queries a media stream output device associated with each media stream to synchronize, and in response receives the current device clock time of each device, each device's next available media stream output time, and each device's delta between available media stream output times. The synchronization manager uses this timing information to determine an earliest available media stream output time common to each media stream output device, and synchronizes the output of the media streams by providing each stream to its associated output device at the earliest available common output time.
Here's Apple's background on the invention: "In a multimedia environment, it is often necessary to synchronize multiple streams of data (e.g., a video stream and an audio stream). Although synchronizing video with audio is a common example, such a challenge occurs whenever it is desired to simultaneously output at least two streams of data of any type that is metered by time.
"Although it is desirable to start each stream at the same time, simply simultaneously sending each media stream to its physical output hardware will not necessarily ensure synchronization. Physical output devices typically have constraints binding available output start times. For example, a video output device can only begin outputting received data at the beginning of a vertical synchronization cycle.
"Other devices such as audio are somewhat more flexible, but still have some inherent latency between the time data is received and the subsequent output time. Latency and constraints on possible output start times are a function of the specific hardware, and thus vary a great deal, not only between media types, but also from device to device.
"When the video and audio streams are output by a common device, synchronization can be achieved by the associated device driver delaying the audio output until a vertical synchronization cycle begins, adjusted for the time of the audio output latency. However, this solution only works for a single device. The synchronizing device driver is not aware of other output devices, and the other output devices and their controlling software have no information concerning the operations of the synchronizing device driver.
"What is needed are methods, systems and computer program products that synchronize multiple media streams, even where the media streams are processed by separate devices."
The inventors are Jeff Moore, Jean-michael Berthoud and Tim Cherma.
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