Apparatus for synchronization of digital multimedia data communicated over wired media
View Patent ↗An apparatus for synchronizing the initiation of the playback of packetized multimedia data received asynchronously in each receiver in a system, and for synchronizing the real time playback in a plurality of receivers in the system, from the transmitter over a wired communications medium. The clocks in the transmitter encoder and the receiver decoders operate asynchronously but at substantially the same rate. Initiation of playback is synchronized according to the arrival time of a first received data packet having a zero-valued retransmit number. Real time playback among a plurality of receivers is synchronized according to a measured time difference between an operating rate of the encoder and an operating rate of the decoder.
1. Apparatus for communicating multimedia data over a wired communication channel, comprising:
a transmitter, operating at a predetermined clock rate, coupled via an interface to the wired communication channel, and further having an encoder for forming data packets having at least a packet sequence number and a packet re-transmit number associated with the data packet; and
a receiver, coupled via an interface to the wired communication channel and having a timer and a decoder, wherein the decoder operates at a clock rate that is substantially the same as the clock rate of the encoder in the transmitter but independent therefrom;
means for receiving user entered signals to cause a channel selection signal to be transmitted from the receiver to the transmitter via the wired communication channel;
means for acknowledging, at each receiver, receipt of a valid received data packet and a correct packet sequence number associated therewith; and
means for synchronizing the initiation of playback of the multimedia data in each receiver according to the arrival time of a first received data packet having a zero-valued re-transmit number.
2. The apparatus of claim 1 , wherein the clock rate of the decoder in the receiver is substantially the same as the clock rate of the encoder in the transmitter within +/−100 parts per million (ppm).
3. The apparatus of claim 1 , wherein the receiver further comprises:
a reserve buffer configured for containing a first threshold number M of received data packets.
4. The apparatus of claim 3 , wherein the first threshold number M is two (2) packets.
5. The apparatus of claim 1 , wherein the receiver further comprises:
a power line interface;
a transceiver and controller section having a network transceiver and a microcontroller coupled between the power line interface and a decoder; and
at least one decoder and two channel digital-to-analog (DAC) coupled in series from an output of the microcontroller for providing a baseband multimedia output signal.
6. The apparatus of claim 3 , wherein the means for synchronizing comprises:
interrupt means responsive to entry of a packet into the reserve buffer in the receiver for initiating decoding of packets to be extracted from the reserve buffer when the reserve buffer is full; and
extraction means for obtaining a data packet from the reserve buffer responsive to initiation of decoding.
7. The apparatus of claim 1 , wherein the means for receiving comprises:
an infrared remote control receiver for receiving infra red signals from a user-operable, infra red remote control transmitter.
8. The apparatus of claim 1 , wherein the means for receiving comprises:
an infra red remote control receiver for receiving signals from a user-operable keypad disposed on the receiver.
9. The apparatus of claim 1 , further comprising:
means for acknowledging, at each receiver, receipt of a valid received data packet and a correct packet sequence number associated therewith; and
means for synchronizing the rate of playback of the multimedia data in each receiver according to a measured time difference between an operating rate of the encoder and an operating rate of the decoder.
10. The apparatus of claim 9 , wherein the clock rate of the decoder in the receiver is substantially the same as the clock rate of the encoder in the transmitter within +/−100 parts per million (ppm).
11. The apparatus of claim 9 , wherein the receiver further comprises:
a reserve buffer in the receiver configured for containing a first threshold number M of received data packets.
12. The apparatus of claim 11 , wherein the first threshold number M is two (2) packets.
13. The apparatus of claim 9 , wherein the receiver further comprises:
a power line interface;
a transceiver and controller section having a network transceiver and a microcontroller coupled between the power line interface and a decoder; and
at least one decoder and two channel digital-to-analog controller (DAC) coupled in series from an output of the microcontroller for providing a baseband multimedia output signal.
14. The apparatus of claim 9 , wherein the means for synchronizing comprises:
first interrupt means responsive to arrival of a packet in the receiver for initiating a count up timer if playback has not already started;
second interrupt means responsive to entry of a packet into the reserve buffer in the receiver for initiating decoding of packets extracted from the reserve buffer when the reserve buffer is full; and
comparison means for determining whether accumulated time in the timer, at the instant extraction for decoding begins, exceeds a predetermined second threshold value N.
15. The apparatus of claim 14 , wherein the predetermined second threshold N is approximately 500 microseconds.
16. The apparatus of claim 14 , wherein the comparison means further comprises:
means for issuing a command to skip the decoding of a sample if the accumulated value in the timer exceeds the predetermined threshold or issuing a command to repeat the decoding of a sample if the value in the timer is less than or equal to the predetermined threshold.