CA2480979C

CA2480979C - Fast channel change

Info

Publication number: CA2480979C
Application number: CA2480979A
Authority: CA
Inventors: Dustin L. Green; James A. Baldwin; Peter T. Barrett
Original assignee: Microsoft Corp; Microsoft Technology Licensing LLC
Current assignee: Microsoft Corp
Priority date: 2003-10-10
Filing date: 2004-09-09
Publication date: 2014-01-14
Anticipated expiration: 2024-09-09
Also published as: JP2005124193A; US20050081244A1; EP1523190A1; CA2480979A1; BRPI0404326B1; KR101150102B1; JP4676738B2; BRPI0404326A8; EP1523190B1; BRPI0404326A; KR20050035071A; MXPA04009351A; US7562375B2; CN1606352B; CN1606352A

Abstract

In an exemplary server implementation, a server is configured to retain at least one independent frame for each video channel of multiple video channels that are being distributed using multicast communications and is adapted to respond to channel change requests from clients by transmitting the retained at least one independent frame of a requested video channel to a requesting client using a unicast communication. In an exemplary method implementation, a method for fast channel changing in a multicast video distribution architecture includes: detecting a channel change request that indicates a requested channel, the requested channel corresponding to a multicast group; and transmitting a retained intra frame for the requested channel as a unicast communication.

Description

1 Fast Channel Change

2

3

4 TECHNICAL FIELD
This disclosure relates in general to changing channels in a digital video 6 environment and in particular, by way of example but not limitation, to reducing 7 the video presentation latency when changing from one video channel to another 8 video channel in a digital multicast network.

BACKGROUND
11 Television-based entertainment systems are expanding the programming 12 and services that they offer. In addition to television programming content such as 13 that found on broadcast and traditional cable networks, television service 14 providers are adding on-demand video, as well as other interactive services, features, and applications. The existence of these specific services, features, and 16 applications, as well as the continuing increase in the breadth of available general 17 programming content, drives the adoption of digital network technology for is television-based entertainment systems.
19 Digital technology enables satellite and cable operators to increase the number and kinds of services that they offer to subscribers and thus their average 21 revenue per subscriber. Unfortunately, although digital technology offers many 22 advantages to subscribers as compared to traditional analog networks, it also has a 23 number of drawbacks. For example, changing channels in a digital television 24 service typically takes longer than in an analog television service.
This channel changing latency annoys and frustrates users of the digital television service.
1 Atty Docket No DOCUMENT IN C:\DOCUMINTS AND

This channel changing latency and other drawbacks of digital technology 2 lead to higher rates of subscriber churn, which means that a large percentage of 3 subscribers that try digital television service switch back to traditional analog 4 service within a short time period. Switching subscribers from analog to digital service involves expenditures for network operators that range from broad, general 6 marketing costs down to individual incentives and installation expenses.
7 Furthermore, network operators usually have greater opportunity and/or ability to 8 sell add-on services (e.g., extra channels, pay-per-view, etc.) in conjunction with 9 digital network services. Consequently, reducing subscriber churn can financially io benefit satellite and cable operators.
I Accordingly, for e.g. television-based entertainment systems, there is a 12 need for schemes and/or techniques to reduce the churn out of digital service and 13 back to traditional analog service that results from subscribers being dissatisfied 14 with the slower channel changing experienced with digital television service.

' 51331-1346 SUMMARY
According to one broad aspect of the invention, there is provided a method for fast channel changing in a multicast video distribution architecture, the method comprising: buffering a multicast video stream segment at a server, the buffered multicast video stream segment including a first retained intra frame and a second retained intra frame, the first retained intra frame being before the second retained intra frame in the buffered multicast video stream segment; detecting a channel change request that indicates a requested channel, the channel change request being from a requesting device, the requested channel corresponding to the buffered multicast video stream segment; determining whether a first next decodable non-intra frame after the first retained intra frame is at least a joining time after a send point of the buffered multicast video stream segment; in response to detecting the channel change request, transmitting to the requesting device a retained intra frame and no dependent frames for the requested channel as a unicast communication for static display, wherein, if the first next decodable non-intra frame after the first retained intra frame is determined to be at least the joining time after the send point of the buffered multicast video stream segment, then the transmitted retained intra frame is the first retained intra frame and the first next decodable non-intra frame after the first retained intra frame is a joining frame, and wherein if the first next decodable non-intra frame after the first retained intra frame is determined to be less than the joining time after the send point of the buffered mutticast video stream segment, then the transmitted retained intra frame is the second retained intra frame and a second next decodable non-intra frame after the second retained intra frame is the joining frame;
and synchronizing a multicast joining operation to a multicast group corresponding to the requested channel, wherein synchronizing includes ensuring the joining frame is the oldest non-intra frame of the buffered multicast video stream segment received by the requesting device in response to the channel change request after the multicast joining operation.
2a ' 51331-1346 According to another broad aspect of the invention, there is provided a method for fast channel changing in a multicast video distribution architecture, the method comprising: sending a channel change request to a server, the channel change request indicating a requested channel, the server buffering a multicast video stream segment, the buffered multicast video stream segment including a first retained intra frame and a second retained intra frame, the first retained intra frame being before the second retained intra frame in the buffered multicast video stream segment, the requested channel corresponding to a multicast group and the buffered multicast video stream segment corresponding to the requested channel, wherein the server determines whether a first next decodable non-intra frame after the first retained intra frame is at least a joining time after a send point of the buffered multicast video stream segment; in response to sending the channel change request, /receiving a retained intra frame for the requested channel as a unicast communication, wherein if the first next decodable non-intra frame after the first retained intra frame is determined to be at least the joining time after the send point of the buffered multicast video stream segment, then the transmitted retained intra frame is the first retained intra frame and the first next decodable non-intra frame after the first retained intra frame is a joining frame, and wherein lithe first next decodable non-intra frame after the first retained intra frame is determined to be less than the joining time after the send point of the buffered multicast video stream segment, then the transmitted retained intra frame is the second retained intra frame and a second next decodable non-intra frame after the second retained intra frame is the joining frame; statically displaying the received retained intra frame; receiving as a multicast communication a portion of the multicast video stream corresponding to the requested channel, wherein the initial multicast frame of the multicast video stream received is the joining frame, the portion including a plurality of consecutive multicast frames of the multicast video stream; and switching from statically displaying the received retained intra frame to displaying the portion of the multicast video stream.
2b " 51331-1346 According to yet another broad aspect of the invention, there is provided one or more non-transitory processor-readable storage media having processor-executable instructions stored thereon, the instructions that, when executed, causing an apparatus to perform the methods described herein.
In an exemplary server implementation, a server is configured to retain at least one independent frame for each video channel of multiple video channels that are being distributed using multicast communications and is adapted to respond to channel change requests from clients by transmitting the retained at least one independent frame of a requested video channel to a requesting client using a unicast communication. In an exemplary method implementation, a method for fast channel changing in a multicast video distribution architecture includes:
detecting a channel change request that indicates a requested channel, the 2c I requested channel corresponding to a multicast group; and transmitting a retained intra frame for the requested channel as a unicast communication.
3 Other method, system, approach, apparatus, server, device, media, 4 procedure, arrangement, etc. implementations are described herein.

7 The same numbers are used throughout the drawings to reference like 8 and/or corresponding aspects, features, and components.
9 FIG. 1 illustrates an exemplary video distribution architecture that includes a network that is capable of both multicast and unicast communications.
FIG. 2 illustrates a video distribution architecture that includes an 12 exemplary channel change server that is capable of providing an intra frame in a 13 unicast message.
14 FIG. 3A illustrates a video distribution architecture that includes an exemplary channel change server that is capable of synchronizing a joining to a 16 multicast group for a client using a join command.
17 FIG. 3B illustrates a video distribution architecture that includes an 18 exemplary channel change server that is capable of synchronizing a joining to a 19 multicast group for a client using a join command and that is capable of providing a smoother initial video presentation experience.
21 FIG. 4A illustrates a first exemplary mechanism for implementing a join 22 command.
23 FIG. 4B illustrates a second exemplary mechanism for implementing a join 24 command.
3 At Docket No DOCUMENT IN C:\DOCUM4NTS AND , 1 FIG. 5 is a flow diagram that illustrates an exemplary method for fast 2 channel changing with a combination multicast and unicast network.

FIG. 1 illustrates an exemplary video distribution architecture 100 that 6 includes a network 104 that is capable of both multicast and unicast communications. Network 104 is implemented with multiple network elements 8 (not separately shown in FIG. 1). Each network element may be capable of facilitating both multicast and unicast communications, or each network element may be capable of facilitating either multicast or unicast communications.

Furthermore, network 104 may include some network elements that participate in 12 both multicast and unicast communications and other network elements that 13 participate in either multicast or unicast communications (but not necessarily 14 both).
As illustrated, a video provider 102, a channel change server 108, and one 16 or more clients 106(1), 106(2) ... 106(n) are coupled to network 104. Video provider 102 is capable of providing video for multiple channels to clients utilizing a multicast scheme over network 104. Likewise, clients 106 are capable 19 of receiving video for multiple channels from video provider 102 via a multicast scheme over network 104. Video as used herein may optionally include audio 21 and/or associated audio/video presentation control information.
22 In a described implementation, video provider 102 receives, stores, and/or otherwise has access to video information for multiple channels as represented by 24 the illustrated video stream 110 for a given particular channel. Each video stream 110 is comprised of independent frames 110(I) and dependent frames 110(D).
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1 Independent frames 110(I) may be decoded without reference to other video 2 frames. Independent frames 110(I) include, for example, intra (I) frames. In 3 contradistinction, dependent frames 110(D) are decoded with reference to one or 4 more other video frames. Dependent frames 110(D) include, for example, predicted (P) frames and bidirectional (B) frames. Consequently, because 6 independent frames 110(I) may be decoded without waiting for any subsequent 7 frames, independent frames 110(1) may be decoded more quickly and/or sooner 8 than dependent frames 110(D), at least for a video stream 110 that is being Generally, video stream 110 is distributed from video provider 102 over ii network 104 to selected clients 106 using a multicast scheme. For example, video 12 provider 102 may correspond to a multicast source, network 104 may include multiple multicast replication points, and clients 106 may correspond to multiple multicast receivers. Furthermore, each video stream 110 for a particular video channel may correspond to a multicast stream in a multicast video distribution 16 scheme.
17 In operation, each given client 106 that requests to receive a particular 18 video channel is joined to a multicast group corresponding to that particular video channel. Thereafter, network 104 forwards a duplicate of the associated video stream 110 for the particular video channel that corresponds to the multicast group 21 to which the given client 106 has been joined. Network 104 forwards duplicates 22 of video stream 110 to selected clients 106 via one or more replication points (not 23 separately shown in FIG 1).
24 When a given client 106 (e.g., client 106(1)) wishes to change channels, client 106(1) transmits a channel change request (CCR) 112 toward a video

5 Atty Docket No DOCUMENT IN C:\DOCUMINTS AND

1 distribution headend or similar server or system. Channel change request 112 2 includes, in addition to an identifier of client 106(1), an indication of the requested 3 video channel. As illustrated, video provider 102 and channel change server 4 separately or jointly comprise a video distribution headend. Channel change request 112 precipitates a multicast group change to a multicast group

6 corresponding to the requested video channel.

7 After the multicast group change, video stream 110 can then be directed to

8 the requesting client 106(1). However, a long channel changing latency may be

9 experienced by the user of client 106(1) if client 106(1) begins receiving video lc; stream 110 during a time period of dependent frames 110(D), which cannot be 11 independently decoded. Client 106(1) waits to decode video until a next 12 independent frame 110(I) is received by client 106(1).
13 In a described implementation, channel change server 108 responds to 14 channel change request 112 to ameliorate this channel changing latency.
Specifically, channel change server 108 is adapted to unicast an independent frame 16 110(1) for the requested video channel to client 106(1). More specifically, channel 17 change server 108 is adapted to transmit a retained independent frame 110(I) for 18 the video stream 110 that is associated with the requested video channel to client 19 106(1) in a unicast communication. This retained independent frame 110(I) may zo then be decoded (and displayed) relatively quickly without regard to other frames 21 110(I or D) and without having to wait for the next independent frame 110(I).
22 Channel change server 108 may operate in any one or more of three 23 exemplary modes when unicasting a retained independent frame. In a first mode, 24 a retained independent frame comprises a cached previous independent frame.
This first mode is described further below with reference to FIG. 2. In a second 6Atty Docket No DOCUMENT IN C:\DOCUMENTS AND ;

1 mode, a retained independent frame comprises a cached previous (or possibly 2 buffered) independent frame. This second mode is described further below with 3 reference to FIG 3A. In a third mode, a retained independent frame comprises a 4 buffered independent frame. This third mode is described further below with reference to FIG. 3B. The second and third modes are implementations that can 6 also involve synchronized joining of clients to a relevant multicast group.
7 FIG. 2 illustrates a video distribution architecture 200 that includes an 8 exemplary channel change server 108 that is capable of providing an intra frame in 9 a unicast message 208. With respect to video distribution architecture 100 (of FIG.
1), video provider 102, channel change server 108, and clients 106(1, 2 ... n) ii remain connected to network 104. However, additional details regarding network 12 104 are provided.
13 As illustrated, network 104 includes at least one replication point 202.
14 Network 104 usually includes many such replication points 202. In fact, multiple replication points 202 are typically located between a multicast source (e.g., video 16 provider 102 and/or channel change server 108) and a multicast receiver (e.g., any 17 client of clients 106). In other words, although only one replication point 202 is 18 explicitly shown, video stream 110 may be communicated (e.g., forwarded and/or 19 duplicated) by multiple replication points 202 between video provider 102 and clients 106.
21 In a described implementation, replication points 202 are realized as any of 22 many different types of network elements or nodes. For example, replication 23 points 202 may be routers, switches, and so forth. As multicast-capable nodes, 24 replication points 202 are adapted to facilitate group membership, to duplicate/forward multicast communications, to handle multicast streams as 7Atty Docket No DOCUMENT IN C:\DOCUMINTS AND

I identified by source and group address (S,G), to perform other multicast-related 2 functions, some combination or subset thereof, and so forth. For example, 3 replication points 202 may be capable of implementing communications in accordance with a multicast routing protocol (e.g., protocol independent multicast ¨ sparse mode (PIM-SM)), in accordance with a group management protocol (e.g., internet group management protocol (IGMP)), and so forth.

is used by receiver hosts (e.g., at least clients 106) and replication 8 points 202 to notify each other about conditions and changes to group membership. PIM-SM is used to propagate forwarding state information between and among replication points 202. IGMP defines messages that are used to join ii clients 106 to a group and to notify replication points 202 that a client 106 is leaving a group. Although an implementation is described primarily in the context 13 of IGMP, other multicast protocols may alternatively be employed.
14 Video stream 110 is illustrated as an exemplary stream of I, P, and B
frames. Video stream 110 may be coded using any video compression algorithm 16 or technology, such as the Moving Pictures Expert Group 4th standard (MPEG-4:

ISO/IEC 14496-1/2/3). The video frame series shown in FIG. 2 is "IBBPBBPBBPBBI"; however, any video frame series may be present. In fact, 19 the frame series for video stream 110 may be changing in an unknown and/or unpredictable fashion.

Channel change server 108 includes one or more processors 206 and at 22 least one memory 204. Memory 204 includes processor-executable instructions 23 that may be executed by processor 206 to perform function(s) as described further 24 below.
These processor-executable instructions may comprise hardware, firmware, software, some combination thereof, and so forth. Modules having 8 Atty Docket No DOCUMENT IN CADOCUMINTS AND

processor-executable instructions that are stored as part of memory 204 include: I
2 frame cacher 214, cached I frames 216, channel change request detector 218, and 3 channel change request handler 220. These modules are described further herein 4 below.
As noted generally above with reference to video stream 110, I frames can 6 be independently decoded, but P and B frames usually cannot. P frames reference 7 up to one other frame, and B frames reference up to two other frames. When a particular client 106 joins a new multicast group corresponding to a different video channel, the particular client 106 is unable to begin decoding video stream 110 (or display any video for the user) until an I frame is received. Under an MPEG-4 ii video coding paradigm, the average delay between a channel change request 112 12 and receipt of an I frame during normal stream flow can be 1-2 seconds. This 13 delay can lengthen to 5-10 seconds with next generation coding paradigms.

Channel change server 108 can reduce this average delay and thereby ameliorate user frustrations arising from long channel changing delays.
16 In a described implementation, client 106(1) initially determines that a 17 video channel change is desired (e.g., as a result of user input) and/or being demanded. Client 106(1) formulates a channel change request 112 that indicates a 19 requested channel and identifies (perhaps implicitly) client 106(1).
Channel change request 112 is transmitted upstream (e.g., as a unicast message) through 21 one or more replication points 202.

Channel change request detector 218 configures channel change server 108 23 to be monitoring network 104 for channel change requests 112. When channel 24 change request 112 from client 106(1) is detected, channel change request handler 220 is activated to respond to it. Specifically, channel change request handler 220 9Atty Docket No DOCUMENT IN C:\DOCUMINTS AND;

1 responds by sending a previous I frame for the requested channel to client 106(1) 2 in a unicast message.
3 In order to be able to send previous I frames for requested channels to 4 clients 106, channel change server 108 secures access to such previous I
frames by retaining them at least temporarily. Specifically, I frame cacher 214 tracks each 6 video stream 110 that is associated with each video channel and stores at least the 7 immediately most recent previous I frame for each video stream 110. These most 8 recent previous I frames are stored as cached I frames 216.
9 As illustrated in FIG. 2, the activation time of channel change request 112 is indicated along video stream 110 as time of CCR 212. This time of CCR 212 falls ii between two I frames. Hence, retained I frame 210, which comprises a cached or 12 previous I frame in this mode, has already been stored at cached I
frames 216 by I
13 frame cacher 214. Channel change request handler 220 extracts retained I
frame 14 210 from cached I frames 216. Channel change request handler 220 also formulates a unicast message (UM) that includes retained I frame 210 and 16 transmits it as retained I frame UM 208 toward client 106(1).
17 Client 106(1) receives retained I frame UM 208 and can decode and display 18 retained I frame 210 thereof while awaiting the next I frame of video stream 110 19 that is associated with the requested channel. The faster that retained I frame UM
208 is received by client 106(1), the shorter the delay between when a user 21 requests a channel change and when a full (initially static) video frame is 22 displayed and the less likely that transmission of retained I frame 210 in retained I
23 frame UM 208 is to interfere with the reception of current and possibly more-24 relevant (e.g., newer) frames of video stream 110. Hence, transmission bandwidth at least between client 106(1) and the replication point 202 that is most proximate 1 ()Any Docket No DOCUMENT IN CADOCUMENTS AND

thereto can be an issue. Addressing this transmission bandwidth issue is described 2 below with reference to FIGS. 3A and 3B.
3 FIG.
3A illustrates a video distribution architecture 300A that includes an exemplary channel change server 108 that is capable of synchronizing a joining to a multicast group for client 106(1) using a join command. With respect to video distribution architecture 200 (of FIG 2), video provider 102, channel change 7 server 108, and clients 106(1, 2 ... n) remain connected to network 104. However, 8 video provider 102 provides video streams 110 via channel change server 108.
9 Although shown separately, video provider 102 and channel change server 108 (e.g., in FIGS. 1-3B) may be co-located and/or combined into a single server or ii system.
12 In a described implementation, channel change server 108 is adapted to 13 buffer video stream 110 to delay it in time before multicast streaming distribution thereof. Channel change server 108 is capable of synchronizing a joining to a new channel to just prior to a new I frame for a video stream 110 that is associated with 16 the new channel by "predicting" the occurrence of a next I frame. This quasi-prediction is accomplished using the time delay aspect of the buffered portion of 18 video stream 110.
19 As illustrated, channel change server 108 includes memory 204 that has processor-executable instructions, which may be executed by processor 206 to 21 perform function(s) as described further below. Modules having processor-executable instructions that are stored as part of memory 204 include: video 23 stream bufferer 304, buffered video stream 306, join command issuer 308, and synchronization determiner 310. The functions of modules 304, 306, 308, and 11 Atty Docket No DOCUMENT IN C ADOCU14NTS AND

I may be implemented in conjunction with or separately from those of modules 214, 2 216, 218, and 220 (of FIG. 2).
3 Channel change server 108 accepts video stream 110 (for each video 4 channel) from video provider 102. Video stream bufferer 304 creates a buffered portion 312(T) of video stream 110 between a receive point (RP) and a send point 6 (SP). Each currently-buffered buffered portion 312 is stored as buffered video 7 stream 306. Buffered portion 312(T) corresponds to a current time "T". The 8 receive point corresponds to the point along video stream 110 at which channel 9 change server 108 is currently receiving from video provider 102. The send point corresponds to the point along video stream 110 at which channel change server 11 108 is currently sending toward clients 106.
12 In a described implementation, client 106(1) transmits upstream (e.g., as a 13 unicast message) channel change request 112, possibly through one or more 14 replication points 202 depending on the upstream path. The activation time of CCR 212 is indicated with respect to video stream 110 and buffered portion 16 312(T). Retained I frame 210 may be sent in retained I frame UM 208 by channel 17 change request handler 220 (as described above with reference to FIG.
2). In this 18 mode, retained I frame 210 comprises a cached or buffered I frame. If the retained 19 I frame 210 happens to be within buffered portion 312(T), it may be retrieved directly from buffered video stream 306, possibly even prior to being cached as 21 part of cached I frames 216 if I frames are not cached until they are sent at the 22 send point SR
23 Because full decoding of true motion video does not start until reception of 24 the next upcoming I frame, transmission of intervening P and/or B frames can be considered unnecessary bandwidth usage. To avoid such bandwidth squandering 1 2Atty Docket No DOCUMENT IN C:\DOCUMENTS AND

1 and to increase the likely speed at which retained I frame UM 208 is received by 4 time to receive the next decodable frame. This may, for example, amount to as 6 much "excess bandwidth" as multiple frames. In this mode, the next decodable 8 Specifically, synchronization determiner 310 ascertains whether the next I
12 within buffered portion 312(T+X). When synchronization determiner 310 16 Join command issuer 308, once activated, issues a join command over 19 302 notifies replication point 202 that client 106(1) is to begin receiving the 24 the latter is described further below with reference to FIG. 4B. In the latter 1 3Atty Docket No. DOCUMENT IN C:\DOCUWNTS AND

1 implementation, the join command that is issued by join command issuer 308 may 2 comprise join message 302.
3 In a described implementation, the size of buffered portion 312 relates to an 4 expected (including a known) time that is consumed when joining a client 106 to a multicast group of a multicast channel. This time may include a time period to 6 effectuate a leave operation. By way of example, buffered portion 312 may 7 correspond to a worst case (e.g., absolute or reasonable worst case) scenario for 8 effectuating a join operation for any of the relevant clients 106.
Alternatively, the 9 size of buffered portion 312 may correspond to an average time to effectuate a io multicast join operation, may be tailored for each individual or designated set of ii clients 106 if conditions of network 104 vary spatially or temporally, and so forth.
12 FIG 3B illustrates a video distribution architecture 300B that includes an 13 exemplary channel change server 108 that is capable of synchronizing a joining to 14 a multicast group for client 106(1) using a join command and that is capable of 15 providing a smoother initial video presentation experience. Video distribution 16 architecture 300A can result in a video gap or discontinuity that is experienced by 17 a user of a client 106. This video gap/discontinuity results from the consecutive 18 display of two non-consecutive I frames, which have multiple intervening un-19 displayed non-I frames. Video distribution architecture 300B ameliorates this 20 video gap/discontinuity by smoothing the video presentation as described below.
21 For the sake of clarity, video stream bufferer 304, join command issuer 308, 22 and synchronization determiner 310 are not shown in FIG. 3B. However, a longer 23 segment of video stream 110 is illustrated. Buffered portion 312(T*) is longer 24 than buffered portion 312(T) (of FIG. 3A). Buffered portion 312(T*) includes a 25 joining time 316 and an I frame interval duration 318, as described below.
1 4Atty Docket No DOCUMENT IN C:\DOCUMVNTS AND
_ In a described implementation for this third mode, channel change server 2 108 is adapted to buffer video stream 110 to delay it in time, before multicast streaming distribution thereof, by at least the maximum distance between I
frames plus the maximum join-time for client 106(1) to become joined to the multicast group corresponding to the requested channel. Channel change server 108 is capable of synchronizing a joining to a new channel to just after a new I
frame for 7 a video stream 110 that is associated with the new channel by "predicting"
the occurrences of I frames. This quasi-prediction is accomplished using the time delay aspect of the buffered portion 312(T*) (e.g., the delay window) of video lo stream 110.

Channel change server 108 is adapted to retain I frames within buffered portion 312(T*). The retained I frames may be retained by I frame cacher 214 as cached I frames 216 or as recorded pointers/indexes to I frames that are in the 14 buffered window. Alternatively, the retained I frames may be retained within is buffered portion 312(T*) without using an I frame cacher 214. In a described 16 implementation for this mode, retained I frame 210 comprises a buffered I frame.

When client 106(1) requests a channel change via a CCR 112, channel 18 change server 108 provides the oldest retained I frame 210 within the delay window of buffered portion 312(T*) for which client 106(1) still has time to receive a retained I frame UM 208 and to join the multicast group in time to receive the frame immediately subsequent to the oldest retained I frame 210.
In this manner, client 106(1) receives a contiguous set of frames, with the first frame 23 being a retained I frame 210 arriving via a retained I frame UM 208 and the (initial) subsequent frames being non-I frames arriving via the multicast group.

Client 106(1) pauses on the retained I frame 210 because it is sent "ahead of time", Atty Docket No. DOCUMENT IN C:\DOCUMFNTS AND

1 and client 106(1) then begins full motion video when it is time to play the 2 immediately subsequent frame that is obtained from the delayed multicast stream.
3 Joining time 316 corresponds to the time consumed when joining a client 4 106 to a multicast group, as described above with reference to FIG. 3A. I
frame interval duration 318 corresponds to the greatest possible time period between 6 successive I frames for the given coding scheme. As illustrated, a first time of 7 CCR 212' is shown arriving just as joining time 316 is about to start.
8 Consequently, a first retained I frame 210', which is a buffered I frame in this 9 implementation of the third mode, and a first next decodable frame 314' are the first two frames that a client 106 receives to start video decoding. A second time ii of CCR 212" is shown arriving after expiration of joining time 316 with respect to 12 retained I frame 210' but prior to expiration of a joining time 316 (not explicitly 13 shown) with respect to retained I frame 210". Consequently, a second retained I
14 frame 210", and a second next decodable frame 314" are the first two frames that a client 106 receives to start video decoding for second time of CCR 212".
16 FIG. 4A illustrates a first exemplary mechanism 308*A for implementing a 17 join command. Exemplary mechanism 308*A involves participation by client 18 as well as channel change server 108 and replication point 202.
Specifically, 19 channel change server 108 transmits a join instruction UM 402 to client 106 via replication point 202. Join instruction UM 402 stipulates to client 106 when to 21 transmit its join message responsive to the determination made by synchronization 22 determiner 310 (of FIGS. 3A and 3B) of channel change server 108. At the 23 appointed stipulated time, client 106 transmits join message 302A to replication 24 point 202 so that client 106 is joined to the multicast group corresponding to the requested channel in time to receive the next decodable frame 314 and without 1 6Atty Docket No DOCUMENT IN CADOCUMENTS AND

1 receiving a significant amount of earlier non-I (or inter) frame(s) or otherwise non-2 decodable frame(s).
3 This joining delay of the multicast stream facilitates bandwidth availability 4 for the unicast delivery of retained I frame 210 (of FIGS. 2, 3A, and 3B).
Replication point 202 may be, for example, the replication point 202 that is closest 6 to client 106 and capable of multicasting the desired video stream 110.
7 To the extent that the join operation is precipitated by a join message 8 that is transmitted from client 106, exemplary mechanism 308*A comports with a 9 more-typical multicast joining procedure. However, the logistics involved are io non-trivial inasmuch as three network elements are involved in the instigation of ii the join message and because setting time constraints (e.g., as reflected by the size 12 of buffered portion 312) becomes concomitantly more difficult and/or more 13 extreme for worst case analysis. The joining procedure can be simpler and more 14 certain if client 106 is not obligated to participate.
FIG. 4B illustrates a second exemplary mechanism 308*B for implementing 16 a join command. Exemplary mechanism 308*B involves participation by channel 17 change server 108 and replication point 202. Specifically, channel change server 18 108 transmits a join message 302B to replication point 202. Join message 302B is 19 transmitted responsive to the determination made by synchronization determiner 310 and likely involves less lead time for effectuating the joining operation with 21 sufficient clearance to receive the next decodable frame 314. Join message 302B
22 notifies replication point 202 that client 106 is to be joined to the multicast group 23 corresponding to the requested channel. Exemplary mechanism 308*B
entails 24 enabling non-receiver hosts, such as sender/source hosts, to be capable of precipitating join operations on behalf of receiver hosts.
1 7Atty Docket No DOCUMENT IN C:\DOCUMENTS AND

1 FIG. 5 is a flow diagram 500 that illustrates an exemplary method for fast 2 channel changing with a combination multicast and unicast network. Flow diagram 500 includes thirteen (13) blocks 502-526. Although the actions of flow diagram 500 may be performed in other environments and with a variety of e.g.
software schemes, FIGS. 2, 3A-3B, and 4A-4B are used in particular to illustrate 6 certain aspects and examples of the method.
7 For example, the actions of blocks 502-526 may be performed by a channel 8 change server 108 and a client 106, possibly in conjunction with one or more replication points 202 of a network 104. As illustrated, channel change server performs the actions of blocks 502-516, and client 106 performs the actions of II blocks 518-526.
12 At block 502, a video stream is accepted. For example, channel change 13 server 108 may accept one or more video streams 110 from an associated video provider 102. At block 504, a portion of the accepted video stream is buffered.
For example, video stream bufferer 304 may delay each video stream 110 that is associated with each channel to create buffered portion 312 for each video stream 17 110.
The buffered portions 312 may be stored as a set of buffered video streams with frames that enter at the receiving point (RP) and "move" toward the 19 sending point (SP).
At block 506, at least one I frame is retained. For example, I frame cacher 21 214 of channel change server 108 may retain the retained frame (e.g., retained I
22 frame 210) of each video stream 110 that is associated with each channel as a set 23 of cached I frames 216 or a set of indexes/pointers to frames in a buffered portion 312(T*). Alternatively, I frames may be retained by being buffered at known or determinable locations of buffered portion 312(T*). As indicated by the dashed 18 Atty Docket No DOCUMENT IN C:\DOCUMFNTS AND

1 arrow that diverges from point 528, the actions of blocks 502-506 are ongoing for 2 channel change server 108.
3 At block 518, video is being received via multicast communication. For example, client 106 may be receiving video stream 110 from video provider 102 and/or channel change server 108 as a multicast stream over one or more replication points 202 of network 104. At block 520, a channel change request is transmitted as a unicast message. For example, client 106 may transmit a channel 8 change request 112 as a unicast message toward channel change server 108. This channel change request 112 is effectively a request to switch from a first multicast group corresponding to a first video channel to a second multicast group ii corresponding to a second video channel, with the requested second video channel 12 being indicated by channel change request 112.
13 At block 508, a channel change request is detected. For example, channel 14 change request detector 218 of channel change server 108 may detect channel change request 112. If video distribution architecture 200 is implemented, channel 16 change server 108 may be monitoring links of and/or interfaces to network 104 in 17 the vicinity of video provider 102 for channel change requests 112, or video provider 102 may be forwarding channel change requests 112 (or channel change 19 server 108 may be the intended recipient of channel change requests 112). If video distribution architecture 300A or 300B is implemented, channel change 21 server 108 may be the intended recipient of channel change requests 112, and so 22 forth.
23 At block 510, a retained I frame for the requested channel is retrieved. For example, channel change request handler 220 accesses cached I frames 216 and/or buffered portion 312(T*) of buffered video stream 306 to retrieve the retained I
1 9Atty Docket No DOCUMENT IN C:\DOCUMFNTS AND

I frame (e.g., retained I frame 210, including 210' and 210") for the video stream associated with the requested channel. At block 512, the retained I frame for 3 the requested channel is transmitted as a unicast message. For example, channel 4 change request handler 220, after appropriate formulation, transmits retained I
frame UM 208 toward client 106.
6 At block 522, the retained I frame for the requested channel is received as a unicast message. For example, client 106 may receive retained I frame UM 208, 8 which is an example of a unicast communication, even though client 106 usually 9 receives video streams 110 as multicast streams during standard video channel to reception. At block 524, the retained I frame for the requested channel is ii displayed. For example, client 106 extracts the retained I frame for the requested channel from the retained I frame UM 208 and causes the retained I frame to be displayed. Depending on the time period until the next decodable frame 314 (including 314' and 314") is due, this static I frame presentation may continue for is a noticeable time (e.g., up to 1-2 seconds in a typical MPEG-4 video coding 16 implementation).
17 At block 514, the client's joining to the multicast group that corresponds to is the requested channel is synchronized with regard to the next decodable frame.
19 For example, for video distribution architectures 300A and 300B, synchronization 20 determiner 310 of channel change server 108 may ascertain when the next decodable frame 314 is due to be sent to (and thereby when next decodable frame 22 314 is likely to be received or will be received in a worst-case scenario by) client 23 106. This next decodable frame 314 ascertainment may be performed with reference to buffered portion 312 (including buffered portion 312(T*) and joining 25 time 316 thereof) for the video stream 110 that is associated with the requested 20Atty Docket No DOCUMENT IN C:\DOCUMFNTS AND

1 channel. Once the timing of next decodable frame 314 is ascertained, 2 synchronization determiner 310 determines the appropriate timing for the 3 multicast joining operation of client 106 to the multicast group corresponding to 4 the requested channel.
At block 516, a join command is issued for the requesting client. For 6 example, join command issuer 308 may issue a join command with respect to 7 client 106 responsive to a synchronization determination by synchronization 8 determiner 310. The join command may comprise a join instruction unicast 9 message 402 that is sent to client 106 to prompt client 106 to transmit a join message 302A at an appointed time to a replication point 202 (e.g., exemplary 11 mechanism 308*A for implementing a join command). Alternatively, the join 12 command may comprise a join message 302B that is sent "directly" to a 13 replication point 202 on behalf of client 106 (e.g., exemplary mechanism 308*B
14 for implementing a join command).
At block 526, video for the requested channel is received via multicast 16 communication. For example, client 106 may receive video stream 110 that is 17 associated with the requested channel via a corresponding multicast streaming 18 group over network 104 using multiple replication points 202. In other words, 19 after a replication point 202 has caused client 106 to be joined to the corresponding multicast streaming group responsive to a join message 302, at least 21 that one replication point 202 duplicates (as necessary) and forwards video stream 22 110 to client 106.
23 The actions of blocks 512 and 516 may, in particular, be performed in a 24 myriad of orders. For example, the issuance of block 516 may occur after the transmission of block 512, or the issuance and transmission of blocks 516 and 21 Atty Docket No DOCUMENT IN CADOCUMENTS AND

1 may occur substantially simultaneously or at least without consideration of the 2 order of either. Alternatively, the issuance of block 516 may be performed after 3 the transmission of block 512 unless a next I frame is of such temporal proximity 4 (e.g., closer than a predetermined threshold period) that waiting to issue the join command jeopardizes the ability of a channel changing client to receive the next I
6 frame.
7 The actions, aspects, features, components, etc. of FIGS. 1-5 are illustrated 8 in diagrams that are divided into multiple blocks. However, the order, 9 interconnections, layout, etc. in which FIGS. 1-5 are described and/or shown is not io intended to be construed as a limitation, and any number of the blocks can be I combined, rearranged, augmented, omitted, etc. in any manner to implement one 12 or more systems, methods, devices, procedures, media, apparatuses, servers, 13 arrangements, etc. for fast channel changing. Furthermore, although the 14 description herein includes references to specific implementations, the illustrated and/or described implementations can be implemented in any suitable hardware, 16 software, firmware, or combination thereof and using any suitable video 17 distribution architecture(s), network element(s) and organization(s), video 18 encoding standard(s), multicast and unicast scheme(s), and so forth.
19 With particular reference to FIGS. 2 and 3A-3B, a video provider 102 and/or a server 108 may include a variety of processor-accessible media. Such 21 media may be any available media that is accessible by a computing or other (e.g., 22 electronic) device. Such media may include both volatile and non-volatile media, 23 removable and non-removable media, and storage (e.g., memory 204) and 24 transmission media (e.g., links or nodes of network 104). The media may include processor-executable instructions.
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1 Implementations for fast channel changing may be described in the general 2 context of processor-executable instructions. Generally, processor-executable 3 instructions include routines, programs, protocols, objects, interfaces, components, 4 data structures, etc. that perform and/or enable particular tasks and/or implement particular abstract data types. Fast channel changing, as described in certain 6 implementations herein, may also be practiced in distributed processing 7 environments where tasks are performed by remotely-linked processing devices 8 that are connected through a communications link and/or network.
Especially but 9 not exclusively in a distributed computing environment, processor-executable instructions may be located in separate storage media, executed by different 11 processors, and/or propagated over transmission media.
12 Although systems, media, devices, methods, procedures, apparatuses, 13 techniques, schemes, approaches, procedures, arrangements, and other 14 implementations have been described in language specific to structural, logical, algorithmic, and functional features and/or diagrams, it is to be understood that the 16 invention defined in the appended claims is not necessarily limited to the specific 17 features or diagrams described. Rather, the specific features and diagrams are 18 disclosed as exemplary forms of implementing the claimed invention.

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Claims

CLAIMS:

1. A method for fast channel changing in a multicast video distribution architecture, the method comprising:
buffering a multicast video stream segment at a server, the buffered multicast video stream segment including a first retained intra frame and a second retained intra frame, the first retained intra frame being before the second retained intra frame in the buffered multicast video stream segment;
detecting a channel change request that indicates a requested channel, the channel change request being from a requesting device, the requested channel corresponding to the buffered multicast video stream segment;
determining whether a first next decodable non-intra frame after the first retained intra frame is at least a joining time after a send point of the buffered multicast video stream segment;
in response to detecting the channel change request, transmitting to the requesting device a retained intra frame and no dependent frames for the requested channel as a unicast communication for static display, wherein, if the first next decodable non-intra frame after the first retained intra frame is determined to be at least the joining time after the send point of the buffered multicast video stream segment, then the transmitted retained intra frame is the first retained intra frame and the first next decodable non-intra frame after the first retained intra frame is a joining frame, and wherein if the first next decodable non-intra frame after the first retained intra frame is determined to be less than the joining time after the send point of the buffered multicast video stream segment, then the transmitted retained intra frame is the second retained intra frame and a second next decodable non-intra frame after the second retained intra frame is the joining frame; and synchronizing a multicast joining operation to a multicast group corresponding to the requested channel, wherein synchronizing includes ensuring the joining frame is the oldest non-intra frame of the buffered multicast video stream segment received by the requesting device in response to the channel change request after the multicast joining operation.

2. The method as recited in claim 1, further comprising:
caching at least one previous intra frame for each channel of a plurality of channels as a set of cached intra frames; and retrieving, responsive to the detecting, the retained intra frame for the requested channel from the set of cached intra frames, the retained intra frame comprising a previous intra frame.

3. The method as recited in claim 1, wherein:
the detecting comprises detecting the channel change request from a particular client; and the transmitting comprises transmitting the retained intra frame to the particular client.

4. The method as recited in claim 1, further comprising:
wherein the joining comprises determining when the retained intra frame reaches a joining time of the buffered video stream portion.

5. A method for fast channel changing in a multicast video distribution architecture, the method comprising:
sending a channel change request to a server, the channel change request indicating a requested channel, the server buffering a multicast video stream segment, the buffered multicast video stream segment including a first retained intra frame and a second retained intra frame, the first retained intra frame being before the second retained intra frame in the buffered multicast video stream segment, the requested channel corresponding to a multicast group and the buffered multicast video stream segment corresponding to the requested channel, wherein the server determines whether a first next decodable non-intra frame after the first retained intra frame is at least a joining time after a send point of the buffered multicast video stream segment;
in response to sending the channel change request, receiving a retained intra frame for the requested channel as a unicast communication, wherein if the first next decodable non-intra frame after the first retained intra frame is determined to be at least the joining time after the send point of the buffered multicast video stream segment, then the transmitted retained intra frame is the first retained intra frame and the first next decodable non-intra frame after the first retained intra frame is a joining frame, and wherein if the first next decodable non-intra frame after the first retained intra frame is determined to be less than the joining time after the send point of the buffered multicast video stream segment, then the transmitted retained intra frame is the second retained intra frame and a second next decodable non-intra frame after the second retained intra frame is the joining frame;
statically displaying the received retained intra frame;
receiving as a multicast communication a portion of the multicast video stream corresponding to the requested channel, wherein the initial multicast frame of the multicast video stream received is the joining frame, the portion including a plurality of consecutive multicast frames of the multicast video stream; and switching from statically displaying the received retained intra frame to displaying the portion of the multicast video stream.

6. One or more non-transitory processor-readable storage media having processor-executable instructions stored thereon, the instructions, when executed, causing an apparatus to perform the method of any one of claims 1 to 5.