FAST CHANNEL SWITCHING FOR DIGITAL TV
A method for digital video distribution in which a program is transmitted as a multicast stream over a network at a base rate. The stream includes a sequence of frames encoding video data, the sequence containing anchor points. A request from a client to begin receiving the program is received at a time subsequent to a given anchor point in the multicast stream. Responsively to the request, a boost stream is transmitted to the client beginning from the given anchor point at an accelerated rate relative to the base rate. The boost stream causes the client to display the video data beginning from the given anchor point and then to join the multicast stream when the boost stream has reached a point of synchronization with the multicast stream.
1 . A method for digital video distribution in which a program is transmitted over a network as a multicast stream at a base rate, the stream including a sequence of frames encoding video data, the sequence containing anchor points, the method comprising:
receiving, at a time subsequent to a given anchor point in the multicast stream, a request from a client to begin receiving the program; and
responsively to the request, transmitting to the client a boost stream beginning from the given anchor point at an accelerated rate relative to the base rate, the boost stream comprising at least a portion of the video data in the multicast stream, so as to cause the client to display the video data beginning from the given anchor point based on the boost stream and then to join the multicast stream when the boost stream has reached a point of synchronization with the multicast stream.
2 . The method according to claim 1 , wherein the given anchor point is a first anchor point, and wherein the point of synchronization is a second anchor point in the multicast stream, subsequent to the first anchor point.
3 . The method according to claim 1 , wherein transmitting the boost stream comprises terminating the boost stream at the point of synchronization.
4 . The method according to claim 1 , wherein transmitting the boost stream comprises continuing to transmit the boost stream to the client at a reduced rate relative to the base rate for a period of time following the point of synchronization, simultaneously with reception of the multicast stream by the client.
5 . The method according to claim 1 , wherein transmitting the boost stream comprises conveying an indication of the point of synchronization to the client, which causes the client to switch over to the multicast stream.
6 . The method according to claim 1 , wherein the sequence of frames comprises intracoded frames (I-frames) interspersed with difference-coded frames, and wherein each of the anchor points corresponds to one of the I-frames.
7 . The method according to claim 1 , wherein the multicast stream is one of multiple channels of video content, which are transmitted to multiple clients, and wherein receiving the request comprises receiving the request from a user viewing a first channel to switch to a second channel.
8 . Communication apparatus, for operation in conjunction with transmission of a program as a multicast stream over a network at a base rate, the stream including a sequence of frames encoding video data, the sequence containing anchor points, the apparatus comprising:
a memory, which is coupled to store the video data; and
boost generation logic, which is coupled to the memory and is arranged to receive, at a time subsequent to a given anchor point in the multicast stream, a request from a client to begin receiving the program, and to transmit to the client, responsively to the request, a boost stream beginning from the given anchor point at an accelerated rate relative to the base rate, the boost stream comprising at least a portion of the video data in the multicast stream, so as to cause the client to display the video data beginning from the given anchor point based on the boost stream, and to cause the client to join the multicast stream when the boost stream reaches a point of synchronization with the multicast stream.
9 . The apparatus according to claim 8 , wherein the given anchor point is a first anchor point, and wherein the point of synchronization is a second anchor point in the multicast stream, subsequent to the first anchor point.
10 . The apparatus according to claim 8 , wherein the boost generation logic is configured to terminate the boost stream at the point of synchronization.
11 . The apparatus according to claim 8 , wherein the boost generation logic is configured to transmit the boost stream to the client at a reduced rate relative to the base rate for a period of time following the point of synchronization, simultaneously with reception of the multicast stream by the client.
12 . The apparatus according to claim 8 , wherein the boost generation logic is configured to convey an indication of the point of synchronization to the client so as to cause the client to send a request to join the multicast stream at the point of synchronization.
13 . The apparatus according to claim 8 , wherein the sequence of frames comprises intracoded frames (I-frames) interspersed with difference-coded frames, and wherein each of the anchor points corresponds to one of the I-frames.
14 . The apparatus according to claim 8 , wherein the multicast stream is one of multiple channels of video content, which are transmitted to multiple clients, and wherein the request comprises an instruction from the user who is viewing a first channel to switch to a second channel.
15 . The transmitter according to claim 14 , wherein the boost generation logic comprises a plurality of builders, which are dynamically assignable to produce boost streams for the multiple channels responsively to boost stream requests from the clients.
16 . A computer software product, for use in conjunction with a multicast transmitter, which transmits a program as a multicast stream over a network at a base rate, the stream including a sequence of frames encoding video data, the sequence containing anchor points, the product comprising a computer-readable medium in which program instructions are stored,
wherein the instructions, when read by a computer associated with the transmitter, cause the computer to receive, at a time subsequent to a given anchor point in the multicast stream, a request from a client to begin receiving the program, and to transmit to the client, responsively to the request, a boost stream beginning from the given anchor point at an accelerated rate relative to the base rate, the boost stream comprising at least a portion of the video data in the multicast stream, so as to cause the client to display the video data beginning from the given anchor point based on the boost stream, and to cause the client to join the multicast stream when the boost stream has reached a point of synchronization with the multicast stream.
17 . The product according to claim 16 , wherein the given anchor point is a first anchor point, and wherein the point of synchronization is a second anchor point in the multicast stream, subsequent to the first anchor point.
18 . The product according to claim 16 , wherein the instructions cause the computer to terminate the boost stream at the point of synchronization.
19 . The product according to claim 16 , wherein the instructions cause the computer to transmit the boost stream to the client at a reduced rate relative to the base rate simultaneously with reception of the multicast stream by the client for a period of time following the point of synchronization.
20 . The product according to claim 16 , wherein the instructions cause the computer to cause the client to send a request to join the multicast stream at the point of synchronization.
21 . A method for digital video distribution in which a program is transmitted as a multicast stream over a network at a base rate, the stream including a sequence of frames encoding video data, the sequence containing anchor points, the method comprising:
transmitting, at a time subsequent to a given anchor point in the multicast stream, a request from a client to begin receiving the program; and
responsively to the request, receiving at the client a boost stream beginning from the given anchor point at an accelerated rate relative to the base rate, the boost stream comprising at least a portion of the video data in the multicast stream;
receiving at the client an indication that the boost stream has reached a point of synchronization with the multicast stream;
responsively to the indication, joining the client to the multicast stream; and
displaying the video data at the client beginning from the given anchor point based initially on the boost stream and then subsequently on the multicast stream.