Media clock recovery
First Claim
1. A system for recovering a local media clock from a master media clock based on a plurality of time-stamped packets received from a transmitter, the system comprising:
- a frequency synthesizer configured to generate the local media clock;
a local real-time counter synchronized with a remote real-time counter associated with the transmitter;
a period determination module configured to determine a period of the local media clock from a change in the local real-time counter over at least one cycle of the local media clock, and to determine a period of the master media clock from a difference between a first timestamp and a second timestamp, a first one of the time-stamped packets including the first timestamp and a second one of the time-stamped packets including the second timestamp;
a syntonization adjustment module configured to cause the frequency synthesizer to adjust a frequency of the local media clock to match a frequency of the master media clock based on a difference between the period of the local media clock and the period of the master media clock; and
a synchronization adjustment module configured to determine a phase difference between the master media clock and the local media clock,where the synchronization adjustment module is further configured to cause the frequency synthesizer to limit the phase difference between the master media clock and the local media clock in response to a determination that the local media clock is syntonized with the master media clock.
3 Assignments
0 Petitions
Accused Products
Abstract
A system recovers a local media clock from a master media clock based on time-stamped packets received from a transmitter. The packets may include audio, video, or a combination of both, sampled at a rate determined by the master media clock at the transmitter. Timestamps in the packets may be based on values of a remote real-time counter at the transmitter that is synchronized with a local real-time counter at a receiver. The local media clock may be syntonized with the master media clock through the clock periods. The clocks may be synchronized by syntonizing the clocks and adjusting the phase of the local media clocks based on timestamps and a real-time counter.
30 Citations
18 Claims
-
1. A system for recovering a local media clock from a master media clock based on a plurality of time-stamped packets received from a transmitter, the system comprising:
-
a frequency synthesizer configured to generate the local media clock; a local real-time counter synchronized with a remote real-time counter associated with the transmitter; a period determination module configured to determine a period of the local media clock from a change in the local real-time counter over at least one cycle of the local media clock, and to determine a period of the master media clock from a difference between a first timestamp and a second timestamp, a first one of the time-stamped packets including the first timestamp and a second one of the time-stamped packets including the second timestamp; a syntonization adjustment module configured to cause the frequency synthesizer to adjust a frequency of the local media clock to match a frequency of the master media clock based on a difference between the period of the local media clock and the period of the master media clock; and a synchronization adjustment module configured to determine a phase difference between the master media clock and the local media clock, where the synchronization adjustment module is further configured to cause the frequency synthesizer to limit the phase difference between the master media clock and the local media clock in response to a determination that the local media clock is syntonized with the master media clock. - View Dependent Claims (2, 3, 4, 5, 6, 7)
-
-
8. An apparatus for recovering a local media clock from a master media clock based on a plurality of time-stamped packets received at the apparatus from a transmitter, the apparatus comprising:
-
a frequency synthesizer that generates the local media clock; a local real-time counter synchronized with a remote real-time counter at the transmitter; a period determination module configured to determine a period of the local media clock from a change in the local real-time counter over at least one cycle of the local media clock, and to determine a period of the master media clock from a difference between at least a first timestamp and a second timestamp in the time-stamped packets, where each of the first and second timestamps is based on a value of the remote real-time counter sampled according to the master media clock at the transmitter; a syntonization adjustment module configured to cause the frequency synthesizer to adjust the period of the local media clock to match the period of the master media clock; and a synchronization adjustment module configured to determine a phase difference between the master media clock and the local media clock, where the synchronization adjustment module is further configured to cause the frequency synthesizer to limit the phase difference between the master media clock and the local media clock in response to a determination that the local media clock is syntonized with the master media clock. - View Dependent Claims (9, 10, 11, 12, 13, 14)
-
-
15. A method that generates a local media clock at a receiver from a plurality of time-stamped packets received from a transmitter, the method comprising:
-
providing a first real-time counter at the receiver, where the first real-time counter is synchronized with a second real-time counter at the transmitter; generating the local media clock with a frequency synthesizer; reading a plurality of first timestamps from the first real-time counter at a first rate determined by the local media clock; determining a period of the local media clock at the receiver based on a change in the first timestamps; determining a period of the master media clock in the transmitter based on a change in a plurality of second timestamps included in the time-stamped packets, the second timestamps being generated from a second real-time counter at the transmitter sampled at a second rate determined by the master media clock;
adjusting a frequency of the local media clock with the frequency synthesizer to limit a difference between the period of the local media clock and the period of the master media clock;determining a phase difference between the master media clock and the local media clock by comparing at least one timestamp in the time-stamped packets with at least one timestamp read from the first real-time counter; and adjusting a phase of the local media clock with the frequency synthesizer to limit the phase difference between the master media clock and the local media clock in response to determining the local media clock is syntonized with the master media clock. - View Dependent Claims (16, 17, 18)
-
Specification