AUDIO BROADCAST RETRANSMISSIONS

1 . A broadcast device configured to broadcast audio streams according to a wireless communications protocol for playout at a plurality of remote devices, each audio stream derived from an audio source and comprising audio data arranged in audio frames, the broadcast device operable in a plurality of retransmission modes wherein audio frames are rebroadcast more frequently in one retransmission mode than another, the broadcast device comprising:

a controller configured to, for each audio stream:

(i) select a retransmission mode based on the audio source of the audio data of that audio stream; and

(ii) select an audio frame to be rebroadcast according to the selected retransmission mode; and

a transmitter configured to rebroadcast the selected audio frame.

2 . A broadcast device as claimed in claim 1 , wherein the wireless communications protocol mandates that the remote devices do not send acknowledgement messages to the broadcast device to confirm receipt of the broadcast audio frames.

3 . A broadcast device as claimed in claim 1 , configured to broadcast audio frames using Connectionless Slave Broadcast of the Bluetooth communications protocol.

4 . A broadcast device as claimed in claim 1 , wherein the controller is configured to select a retransmission mode having a lower frequency of rebroadcasts compared to other ones of the plurality of retransmission modes when the audio source is a remote audio source and the broadcast device receives the audio data from that remote audio source over a radio link.

5 . A broadcast device as claimed in claim 4 , wherein the radio link is an A2DP link of the Bluetooth communications protocol.

6 . A broadcast device as claimed in claim 1 , wherein the controller is configured to select a retransmission mode having a higher frequency of rebroadcasts compared to other ones of the plurality of retransmission modes when the broadcast device receives the audio data from an audio source over a non-radio link.

7 . A broadcast device as claimed in claim 6 , wherein the non-radio link is a USB link.

8 . A broadcast device as claimed in claim 1 , wherein the controller is configured to control the transmitter to broadcast an audio frame which has not been previously broadcast in preference to rebroadcasting another audio frame.

9 . A broadcast device as claimed in claim 1 , wherein the wireless communications protocol mandates that communications take place in time slots, and the controller is configured to, based on the selected retransmission mode, determine to use a time slot either (i) to rebroadcast an audio frame or (ii) for another function.

10 . A broadcast device as claimed in claim 1 , wherein the controller is configured to, based on the selected retransmission mode, set parameters of the selected audio frame to be rebroadcast.

11 . A broadcast device as claimed in claim 10 , wherein the controller is configured to, based on the selected retransmission mode, set a transmission power level of the selected audio frame to be rebroadcast.

12 . A broadcast device as claimed in claim 1 , wherein the wireless communications protocol mandates that communications take place in time slots, and wherein the transmitter is configured to broadcast a plurality of audio frames in a single time slot, the controller being configured to:

select for broadcast in the single time slot, available audio frames which have not previously been broadcast;

select for rebroadcast in the single time slot, further audio frames according to a selection process in which those audio frames having a higher broadcast priority are selected in preference to those audio frames having a lower broadcast priority; and

control the transmitter to transmit the selected available audio frames and the selected further audio frames.

13 . A broadcast device as claimed in claim 12 , wherein the controller is configured to select a number of further audio frames so as to fill up the remainder of the single time slot that is not used for the available audio frames.

14 . A broadcast device as claimed in claim 12 , wherein each audio frame comprises audio data and a playout time, the playout time indicative of a time at which the audio data is to be played out at the remote devices, wherein an audio frame is only available for broadcast if it is within a broadcast time window.

15 . A broadcast device as claimed in claim 14 , wherein the broadcast time window has an upper bound which is the current time plus a first offset, and a lower bound which is the current time plus a second offset, and wherein an audio frame is within the broadcast time window when its playout time is between the upper bound and the lower bound.

16 . A broadcast device as claimed in claim 12 , wherein the fewer times an audio frame has been broadcast the higher its broadcast priority.

17 . A broadcast device as claimed in claim 14 , wherein the closer the playout time of an audio frame to a lower bound of the broadcast time window, the higher its broadcast priority.

18 . A remote device configured to receive broadcast audio streams according to a wireless communications protocol, each audio stream comprising audio data arranged in audio frames, the remote device being configured to:

receive a broadcast audio frame;

compare the playout time of the received audio frame with playout times of previously received audio frames;

if the playout time of the received audio frame corresponds to the playout time of a previously received audio frame, discard the received audio frame;

if the playout time of the received audio frame does not correspond to the playout time of a previously received audio frame:

store the audio data and the playout time of the received audio frame; and

playout the audio data at the playout time.

19 . A method of broadcasting audio streams from a broadcast device according to a wireless communications protocol for playout at a plurality of remote devices, each audio stream comprising audio data arranged in audio frames, the broadcast device having a plurality of retransmission modes wherein audio frames are rebroadcast more frequently in one retransmission mode than another, the method comprising:

for each audio stream, selecting a retransmission mode based on the audio source of the audio data of that audio stream;

selecting an audio frame to be rebroadcast according to the selected retransmission mode; and

rebroadcasting the selected audio frame.

20 . A method as claimed in claim 19 , comprising selecting a retransmission mode having a lower frequency of rebroadcasts compared to other ones of the plurality of retransmission modes when the audio source is a remote audio source and the audio data is received from the remote audio source over a radio link.