Synchronized audio/video decoding for network devices

• US 20060233203A1
• Filed: 03/20/2006
• Published: 10/19/2006
• Est. Priority Date: 04/13/2005
• Status: Active Grant

• Current Assignee: Sony Corporation (Sony Group Corp.), Sony Electronics Inc. (Sony Group Corp.)
• Original Assignee: Sony Corporation (Sony Group Corp.), Sony Electronics Inc. (Sony Group Corp.)
• Inventors: Iwamura, Ryuichi
• Granted Patent: US 8,238,376 B2
• Time in Patent Office: Days
• US Class Current: 370/516
• CPC Class Codes: H04N 21/2368 Multiplexing of audio and video streams
• CPC Class Codes: H04N 21/4305 Synchronising client clock from received content stream, e.g. locking decoder clock with encoder clock, extraction of the PCR packets arrangements for synchronising receiver with transmitter by comparing receiver clock with transmitter clock H04L7/0012; arrangements for synchronising receiver with transmitter wherein the receiver takes measures against momentary loss of synchronisation H04L7/0083
• CPC Class Codes: H04N 21/4341 Demultiplexing of audio and video streams
• CPC Class Codes: H04N 21/43615 Interfacing a Home Network, e.g. for connecting the client to a plurality of peripherals home Audio Video Interoperability [HAVI] data switching networks H04L12/2805

Abstract

A method of synchronizing decoders within a network to a server includes receiving a set of timestamps and local clock signals upon receiving the beacon interrupt signal, computing differential timestamp and local clock values based on values of timestamp and local clock signals, respectively, within the sets of timestamp and local clock signals, determining whether the differential local clock value has a predetermined relationship with the differential timestamp value, and transmitting a clock rate adjustment command signal to the decoder when differential local clock value does not have the predetermined relationship with the differential timestamp value. The clock rate adjustment command signal adjusts the local system time clock of the decoder such that a subsequent differential clock value will have the predetermined relationship with the differential timestamp value. When this method is performed for each decoder within the network, the decoders are substantially synchronized and the decoding delay can be kept below humanly perceptible levels.

Claims

1. A method of synchronizing a decoder within a network to a server, comprising:

receiving a set of timestamp signals, each timestamp signal within the set of timestamp signals having a value corresponding to a timestamped beacon transmitted by a network server, the network server adapted to stream encoded data over a network;

receiving a set of local clock signals, each local clock signal within the set of local clock signals having a value generated by a local system time clock associated with a decoder of a network client, the decoder adapted to decode the encoded data;

computing a differential timestamp value based on values of timestamp signals within the set of timestamp signals;

computing a differential local clock value based on values of local clock signals within the set of local clock signals;

determining whether the differential local clock value has a predetermined relationship with respect to the differential timestamp value; and

transmitting a clock rate adjustment command signal to the decoder when it is determined that the differential local clock value does not have the predetermined relationship with the differential timestamp value, the clock rate adjustment command signal adapted to adjust the local system time clock such that a subsequent differential local clock value will have the predetermined relationship with the differential timestamp value.

2. The method of claim 1, further comprising:

receiving a beacon interrupt signal from a network interface associated with the network client, the beacon interrupt signal generated by the network interface upon receipt of a beacon transmitted by the network server, wherein

each timestamp signal of the set of timestamp signals is received from the network interface and has a value corresponding to a beacon interrupt signal.

3. The method of claim 1, further comprising:

receiving a beacon interrupt signal from a network interface associated with the network client, the beacon interrupt signal generated by the network interface upon receipt of a beacon transmitted by the network server, wherein

each local clock signal of the set of local clock signals is received from the local system time clock and has a value corresponding to a beacon interrupt signal.

4. The method of claim 1, further comprising:

receiving the sets of timestamp and local clock signals within a period during which a predetermined number of beacons are output by the network server; and

transmitting the clock rate adjustment command signal to the decoder before a beacon is output subsequent to the period.

5. The method of claim 1, wherein the clock rate adjustment command signal is adapted to increase the frequency of the local system time clock when the differential local clock value is less than the differential timestamp value.

6. The method of claim 1, wherein the clock rate adjustment command signal is adapted to decrease the frequency of the local system time clock when the differential local clock value is greater than the differential timestamp value.

7. The method of claim 1, further comprising:

receiving a system time clock preset command signal; and

transmitting the system time clock preset command signal to the local system time clock, the system time clock preset command signal adapted to set the local system time clock to a specific preset value upon transmission of a beacon by the network server.

8. The method of claim 1, further comprising:

receiving a decode start signal after transmitting the clock rate adjustment command signal; and

transmitting the decode start signal to the decoder, wherein decode start signal is adapted to cause the decoder to decode the encoded data upon transmission of a beacon by the network server.

9. The method of claim 1, further comprising:

determining whether a buffer occupancy of a local buffer of the decoder is within a predetermined range of a total buffer occupancy as the decoder decodes encoded data within the local buffer; and

transmitting a data stream control command signal to the network server when it is determined that the buffer occupancy is outside the predetermined range, the data stream control command signal adapted to alter a then current data streaming characteristic of the network server.

10. The method of claim 9, wherein the data stream control command signal is adapted to cause the network server to stop streaming data when it is determined that the buffer occupancy exceeds an upper threshold of the predetermined range.

11. The method of claim 9, wherein the data stream control command signal is adapted to cause the network server to resume streaming data when it is determined that the buffer occupancy exceeds a lower threshold of the predetermined range.

12. The method of claim 1, further comprising:

determining whether a buffer occupancy of a local buffer of the decoder is within a predetermined range of a total buffer occupancy as the decoder decodes encoded data within the local buffer;

transmitting a clock rate control command signal to the network server when it is determined that the buffer occupancy is outside the predetermined range;

receiving a clock ratio adjustment signal corresponding to the clock rate control command signal, the clock ratio adjustment signal containing a clock adjustment ratio;

computing the clock rate adjustment command signal based on the clock adjustment ratio; and

transmitting the computed clock rate adjustment command signal to the decoder to adjust the local system time clock such that a subsequent differential local clock value is within the predetermined range of the total buffer occupancy.

13. The method of claim 12, wherein the clock rate adjustment command signal is adapted to increase the frequency of the local system time clock when it is determined that the buffer occupancy exceeds an upper threshold of the predetermined range.

14. The method of claim 12, wherein the clock rate adjustment command signal is adapted to decrease the frequency of the local system time clock when it is determined that the buffer occupancy exceeds a lower threshold of the predetermined range.

15. A network device, comprising:

a network interface adapted to receive encoded data transmitted over a network;

a decoder coupled to the network interface adapted to decode the received encoded data; and

a processor coupled to the network interface and decoder, the processor containing circuitry adapted to;

receive a set of timestamp signals via the network interface, wherein each timestamp signal within the set of timestamp signals has a value corresponding to a timestamped beacon transmitted by a network server;

receive a set of local clock signals, wherein each local clock signal within the set of local clock signals has a value generated by a local system time clock associated with the decoder;

compute a differential timestamp value based on values of timestamp signals within the set of timestamp signals;

compute a differential local clock value based on values of local clock signals within the set of local clock signals;

determine whether the differential local clock value has a predetermined relationship with respect to the differential timestamp value; and

transmit a clock rate adjustment command signal to the decoder when it is determined that the differential local clock value does not have the predetermined relationship with the differential timestamp value, wherein the clock rate adjustment command signal is adapted to adjust the local system time clock such that a subsequent differential local clock value will have the predetermined relationship with the differential timestamp value.

16. The network device of claim 15, wherein the clock rate adjustment command signal is adapted to increase the frequency of the local system time clock when the differential local clock value is less than the differential timestamp value and to decrease the frequency of the local system time clock when the differential local clock value is greater than the differential timestamp value.

17. The network device of claim 15, wherein

the decoder includes a local buffer adapted to store encoded data;

the decoder is adapted to decode the encoded data stored within the local buffer; and

the processor contains circuitry further adapted to;

determine whether a buffer occupancy of the local buffer is within a predetermined range of a total buffer occupancy; and

transmit a data stream control command signal to the network server when it is determined that the buffer occupancy is outside the predetermined range, wherein the data stream control command signal adapted to alter a then current data streaming characteristic of the network server.

18. The network device of claim 15, wherein

the decoder includes a local buffer adapted to store encoded data;

the decoder is adapted to decode the encoded data stored within the local buffer; and

the processor contains circuitry further adapted to;

determine whether a buffer occupancy of the local buffer is within a predetermined range of a total buffer occupancy;

transmit a clock rate control command signal to the network server when it is determined that the buffer occupancy is outside the predetermined range;

receive a clock ratio adjustment signal corresponding to the clock rate control command signal, the clock ratio adjustment signal containing a clock adjustment ratio;

compute the clock rate adjustment command signal based on the clock adjustment ratio; and

transmit the computed clock rate adjustment command signal to the decoder to adjust the local system time clock such that a subsequent differential local clock value is within the predetermined range of the total buffer occupancy.