Method and apparatus for expediting delivery of programming content over a broadband network
A method is provided that is performed by a client device such a set top box when a viewer requests a program by initiating a channel change from a program guide or entering a channel through the user interface. The client device receives the user request and, in response, the client device transmits the request to the streaming server in the headend, which causes the streaming server to create a unicast catch up stream that commences with a key frame. The streaming server calculates the end point of the catch up stream and continues to send the catch up stream at a rate faster than real time. The client device receives the catch up stream and begins buffering it. While the catch up stream is being buffered the client device begins decoding and presenting the content. The client device receives the end of stream marker, and in response, sends a request to join the multicast stream. Once the client device starts receiving the multicast stream, the client device discards any remaining images or pictures in the catch up stream that precede the synchronization time. The client device also begins to buffer the multicast stream as it continues to play the buffered catch up stream. When it reaches the end of the catch up stream, the client device begins to play out the buffered multicast stream.
1. A method to expedite delivery of programming to a user over a broadband network, the method comprising:
receiving a scalably encoded programming stream including a base layer and an enhancement layer;
receiving from the user a request for programming over the broadband network;
in response to the request, transmitting to the user over the broadband network a unicast stream in parallel to a corresponding multicast stream that includes the scalably encoded programming stream, wherein the unicast stream includes the base layer but not the enhancement layer, further wherein the base layer defines a reduced bit rate representation of the requested programming, wherein the reduced bit rate representation is encoded at a reduced bit rate and a lower spatial resolution rate relative to a normal representation of the requested programming that is encoded for transmission over the broadband network at a target bit rate wherein the unicast stream is transmitted at a rate faster than that of the multicast stream,
wherein the enhancement layer is only decodable in conjunction with the base layer and contains references to the base layer to thereby generate the normal representation of the requested programming, said normal representation having an increased spatial resolution relative to the reduced bit rate representation of the base layer; and
terminating transmission of the unicast stream at a time arising not before (i) the normal representation is multicast over the broadband network as a multicast stream and (ii) the unicast stream and the multicast stream are received by the user in temporal synchronization with one another.
2. The method of claim 1 wherein a duration T of the unicast stream is equal to T=CR*I k , where
CR
=
R
t
R
t
-
R
c
,
R t is the target bit rate, R c is the reduced bit rate and I k is equal to a time interval between successive key frames in the multicast stream.
3. The method of claim 2 wherein the key frames are I frames.
4. The method of claim 1 wherein the unicast stream is forwarded at a bit rate at which the normal representation of the requested programming is encoded.
5. The method of claim 1 further comprising receiving in parallel the unicast stream and the multicast stream as two separate program streams.
6. The method of claim 5 wherein the unicast and multicast streams share a common time base.
7. The method of claim 1 further comprising: identifying a Packet ID (PID) assigned to packets associated with the base layer and a PID assigned to packets associated with the enhancement layer; and dropping the packets associated with the enhancement layer to generate the reduced bit rate representation of the required programming.
8. The method of claim 7 further comprising dropping padding packets associated with the enhancement layer before generating the reduced bit rate representation of the requested programming.
9. The method of claim 8 further comprising assigning a new PID value to the dropped padding packets before they are dropped, and reassigning an original PID value to the dropped padding packets prior to inclusion of the dropped padding packets in the multicast stream.
10. The method of claim 1 further comprising generating a marker packet for inclusion with the unicast stream, wherein the marker packet denotes an end of a stream point.
11. An apparatus for a broadband network, comprising:
a scalable encoder for receiving programming content and generating a scalably encoded programming stream therefrom, the scalably encoded programming stream including a base layer and an enhancement layer, the base layer defining a reduced bit rate representation of the programming content, said reduced bit rate representation having a lower spatial resolution relative to a normal representation, wherein the enhancement layer is only decodable in conjunction with the base layer and contains references to the base layer to thereby generate the normal representation, said normal representation having an increased spatial resolution relative to the reduced bit rate representation of the base layer; and
a streaming server for receiving the scalably encoded programming stream, wherein the streaming server, responsive to a user request for the programming content, is configured to output for transmission over the broadband network a catch up bit stream, having a key frame, at a bit rate at which the scalably encoded programming stream is encoded, wherein the catch up bit stream includes the base layer but not the enhancement layer,
wherein the streaming server is further configured to terminate transmission of the catch up bit stream at a time arising not before (i) the normal representation is multicast over the broadband network as a multicast stream and (ii) the catch up bit stream and the multicast stream are received by a user in temporal synchronization with one another.
12. The apparatus of claim 11 wherein the streaming server is further configured to unicast the catch up bit stream to the user.
13. The apparatus of claim 11 wherein the streaming server is further configured to multicast the scalably encoded programming stream, including both the base layer and enhancement layer, over the broadband network.
14. The apparatus of claim 11 wherein the streaming server is further configured to identify packets associated with the base layer and packets associated with the enhancement layer and to drop the packets associated with the enhancement layer to generate the catch up bit stream.
15. A device, comprising:
a user interface for requesting a selected program for receipt over a broadband network, wherein the selected program is received as a scalably encoded programming stream including a base layer and an enhancement layer;
a front-end for receiving at a target bit rate over the broadband network an initial portion and a remaining portion of the selected program, the initial portion being arranged as a unicast stream, wherein the unicast stream includes the base layer but not the enhancement layer, further wherein the base layer defines a reduced bit rate representation of the selected program, wherein the reduced bit rate representation is encoded at a reduced bit rate and a lower spatial resolution relative to a normal representation of the requested programming that is encoded for transmission over the broadband network at the target bit rate,
wherein receiving of the unicast stream is terminated at a time arising not before (i) the normal representation is received as a multicast stream over the broadband network and (ii) the unicast stream and the multicast stream are received in temporal synchronization with one another,
wherein the enhancement layer is only decodable in conjunction with the base layer and contains references to the base layer to thereby generate the normal representation of the requested programming, said normal representation having an increased spatial resolution relative to the reduced bit rate representation of the base layer;
a buffer for buffering at least the unicast stream;
a decoder for decoding the unicast stream received from the buffer at the target bit rate; and
a processor operatively associated with the user interface, the front-end, the buffer and the decoder.
16. The device of claim 15 wherein the decoder is a scalable decoder.
17. The device of claim 15 wherein the processor is configured to send a multicast join request to receive the remaining portion of the selected program as a multicast stream.
18. The device of claim 15 wherein the processor is configured to send a multicast join request when an end of stream marker packet is detected indicating an end point of the initial portion of the selected program.