GB2516386A - Media substitution system - Google Patents

Abstract

Outputting an audiovisual (A/V) substitutional media item within a media output stream at a media output device, wherein the media output stream comprises a video stream and an audio stream, and the media output stream includes a splice-in point and a splice-out point, the method comprising outputting dummy audio content subsequent to the audio content of the substitutional media item if the output of the audio content of the substitutional media item occurs before the splice-out point. The dummy audio content may comprise one or more audio frames synchronised with the audio stream of the media output stream. This targeted advertising system may output a few locally-generated mute audio frames if the video and audio signals have become out-of-sync.

Description

Field of the Invention

[0001] The present invention relates to a programme distribution system with local media

S Background of the Invention

[0002] Media substitution systems involve the selection of a media item for output by a receiver during a prcdefined slot in a scheduk either at time of broadcast or when playing back recorded or video-on-demand (VOD) programming. such as from a Personal Video Recorder (PVR). Such systems may be used for substitutional advertising, for example.

where an advertisement (a commercial in US English) is selected for output based on a predefined user profile. without specific selection of the advertisement by the user. In a broadcast example, thc user experience is similar to watching a broadcast with an advertising break, but the advertisements are tailored to the user profile by means of a selection made at the broadcast receiver. A delault media item may he included in the broadcast channel during the slot, for output by receivers in which media insertion is not enabled or receivers not targeted by the substitution.

[0003] Attempts have been made to standardise aspects of media substitution. For example, the Society of Cable Telecommunications Engineers standard SCTE 130-1 2008 defines a framework of XML interface standards for communication between different components of a substitutional advertising platform. The Advanced Advertising 1.0 specification was announced by Canoe Ventures LLC on 30 March 2009.

[0004] However, the practical implementation of a media substitution system raises many challenges. One problem is the complexity of scheduling media items that are subject to constraints, for example relating to other media items to be scheduled or to scheduled programmes, particularly when output proximate or adjacent to each other. Constraints in current linear (i.e. non-substitutional) advertisement scheduling systems already involve a considerable level of complexity. For example. the applicant's Landmark 2 system requires a dedicated state of the art computer system to perform the constraint satisfaction necessary to manage advertisement scheduling in over 200 channels. A corresponding substitutional system would involve an unmanageable level of complexity if constraints were to he satisfied between all possible substitutional options.

[00051 lii a centralised broadcast system, such as a satellite broadcast system. regional variations in the media items must be handled by means of substitution, rather than by transmitting regional variations only from the corresponding regional headends.

[0006] Another problem with media substitution involves determination of which media items have been output at the receiver. Currently, such information is obtained from survey data from a relatively small number of users, although more accurate information could he provided over a return link. However, the receiver may not have a return link available, or it may be desirable to avoid using the return link, for example where the return channel is over a dial-up modem connectable to the user's main telephone line.

Users may also be averse to systems which report specific user behaviour to a remote site.

[0007] Another problem involves the method of selecting the substitutional media items to he output by the receiver, according to the user profile. It would he desirable for the selection criteria to be as flexible as possible, but this would involve stonng a large quantity of profile data at the receiver. Furthermore, the broadcast receiver may not be capable of applying complex selection rules to determine which media item to output.

[0008] Another problem arising from substitutional media insertion is the need to make the transition in an output stream between a broadcast or playback progranmie and a substitutional item as seamless as possible. Ideally, the transition should he imperceptible to the user, so that the user experience is indistinguishable from watching a media item, such as an advertisement, included as part of a broadcast or playback programme.

However, the use of digitally encoded video and audio data presents particular problems in splicing a substitutional media item into an output stream.

[0009] Digital video broadcasts typically comply with the DVB standards, such as DVB-T for terrestrial and DVB-S for sateflitc, which specify the usc of interframe video compression such as MPEG-2. Therefore, at least some of the video frames are encoded with reference to a preceding frame (P frames) or with reference to preceding and following frames (B frames). Splicing one video stream into another video stream may disrupt the encoding scheme, for example if a B frame of one stream is followed by a P or B frame of the other stream, such that severe decoding errors occur.

[0010] At least some of the video frames may have an associated time reference, such as the presentation time stamp (PTS) induded in MPEG-2 video streams, to assist with audio synchronisation. The time reference of a broadcast stream may indicate the time of broadcast. However, a substitutional media item will typically have a completely different time reference from the broadcast or playback stream. When a substitutional media item is spliced into a broadcast stream, the resultant discontinuity in time references may cause problems in the audio and video decoders, such as loss of audio synchronisation or audio muting.

[0011] Audio decoding of substitutional content presents a particular problem, since audio decoding may be performed by an external decoder that is not aware of when splicing has occurred, and is not designed to handle spliced audio content. Any apparent errors in the audio stream caused by splicing will lead to unpredictable results at the audio decoder.

[0012] Another problem may incur in the indication of splice points to a broadcast encoder. The system upstream of the encoder indicates the splice points using a time reference, while the encoder encodes the splice point with reference to a specific video frame. Since the indicated time may not correspond precisely to the start of an encoded frame, there is an uncertainty of up to one frame penod in the encoded position of the splice point.

[0013] The above problems are not confined to broadcast systems. since video on demand (VOD) and push video on demand systems (PVOD) may include substitutional content with a requested programme; see for example the applicant's patent publication WO 2008/078093 Al, concerning the Unking of secondary assets, such as advertisements, with a primary asset, such as a requested programme.

Statement of the Invention

[0014] According to the present invention, there is provided a method according to claim [0015] An embodiment of the invention includes a method of outputting an audiovisual substitutional media item within a media output stream at a media output device, wherein the media output stream comprises a video stream and an audio stream having mutually different frame rates, and the media output stream indudes a video splice-in point referenced to a video frame of the video stream, the method comprising deriving an audio splice-in point as an audio frame of the media output stream at or immediately after the video splice-in point, and outputting the audio content of the suhstitutiona media item from the audio splice-in point.

[0016] An embodiment of the invention includes a method of outputting an audiovisual substitutional media item within a media output stream at a media output device, wherein the media output stream compnses a video stream and an audio stream having mutually different frame rates, wherein the audio content of the substitutional media item is output with a frame timing synchronised to the audio stream of the media output stream.

[0017] An embodiment of the invention includes a method ol outputting an audiovisual substitutional media item within a media output stream at a media output device, wherein the media output stream comprises a video stream and an audio stream, and the media output stream includes a splice-in point, wherein the audio content ol the media output stream is decoded from encoded audio data and, if the encoded audio data for the media output stream immediately before the splice-in point arrives too late to be output before the audio content of the substitutional media item from the splice-in point, outputting dummy audio content prior to the splice-in point instead of the audio content of the media output stream.

[0018] An embodiment of the invention includes a method of outputting an audiovisual substitutional media item within a media output stream at a media output device, wherein the media output stream comprises a video stream and an audio stream, and the media output stream includes a splice-in point and a sphce-out point, the method comprising outputting dummy audio content subsequent to the audio content of the substitutional media item ii the output of the audio content ol the substitutional media item occurs before the spbce-out point. The dummy audio content may comprise one or more audio frames synehronised with the audio stream of the media output stream.

[0019] An embodiment of the invention includes a method of encoding a framed media stream at an encoder for broadcast at a headend. the encoded media output stream including a splice point message referenced to a frame of the media stream at a time indicated by a media scheduler, the method comprising synehronising the frame timing of the encoder to the timing of the media scheduler.

Brief Description of the Drawings

[0020] There now follows, by way of example only, a detailed description of embodiments of the present invention, with reference to the figures identified below.

Figure 1 is a schematic diagram of the main components of a media substitution system in an embodiment of the present invention.

Figure 2 is a flowchart of the steps involved in the operation of the media Figure 3 is a flowchart of steps performed by the receiver in determining which media items to acquire.

Figure 4a is an entity relationship diagram for the attributes of a non-aggregated campaign.

Figure 4h is an entity relationship diagram for the attributes of an aggregated Figure 5 is a diagram of a substitutional slot containing a single advertiser multiple copy campaign, in an embodiment of the invention.

Figure 6 is a diagram of a substitutional slot containing three multiple advertiser single copy campaigns, in an embodiment of the invention.

Figure 7 is a diagram illustrating the scheduling of an aggregate substitutional campaign into a slot, in an embodiment of the invention.

Figure 8 is a diagram of a first embodiment of a splicing architecture.

Figure 9 is a diagram of a second embodiment of a splicing architecture.

Figure 10 is a diagram of the frame timing of encoded input, substitutional and output video in a first splicing embodiment.

Figure II is a diagram of the frame timing of encoded input, substitutional and output video in a second splicing embodiment.

Figure 12 is a diagram of a broadcast stream and corresponding receiver output in an embodiment of the invention.

Detailed Description of the Embodiments

[0021] Figure 1 shows schematically the main components of a media substitution system in an embodiment of the present invention, in which the programmes are video broadcast programmes and the substitutional media items comprise advertising video clips.

[0022] A sample broadcast receiver I comprises a personal video recorder (PVR) arranged to receive broadcast channels from a headend 2 over a broadcast link, and to output at least one of the received broadcast channels to a video display 3. The receiver 1 stores profile data 5 identifying preferences andlor demographics of one or more users or subscribers associated with the receiver I. The receiver I also stores media content 4, compnsing substitutional media items and associated metadata. The media items may be received over the broadcast link or another communications network link, in advance of their scheduled broadcast time.

[0023] A media insertion function 6 detects the occurrence of a substitutional slot in a currently received broadcast programme, and may select a substitutional media item for output to the video display during the substitutional slot, in place of the linear media content on the broadcast channel, based on the proffle data. The linear media content will he output by broadcast receivers for which substitution is not enabled, either because the receiver is not capable of media substitution or because media substitution is inhibited.

The linear media content will also be output by receivers for which substitution is enabled, but the profile data does not match the segments of any of the substitutional media items for that suhstitutiona slot.

[0024] Optionally, the PVR may record viewing data 7 indicating the broadcast programmes and/or media items output for display by the receiver 1. for reporting purposes.

[0025] Descriptions of the media content 4 necessary for the receivers I are compiled by a central scheduling function 8. which detemilnes the scheduling of the media content 4.

The media content 4 is output to a media broadcast function 9 for broadcast to the receivers I in advance of the scheduled times of the media content. The scheduling function 8 also outputs linear media items for insertion in a broadcast programme schedule executed by a progranmie broadcast function 10.

[0026] All the substitutional media items for a substitutional slot should be broadcast before the occurrence of the substitutional slot in the broadcast schedule. In some circumstances, each item should he broadcast multiple times to maximize the chance that all items are received by most of the receivers 1, in case some of the receivers are occasionally switched off or unable to receive broadcasts. However, it is not essential that all substitutional options be received by all receivers, since the linear content broadcast during the slot may be output if the required substitutional option is unavailable.

[0027] The profile data 5 stored on the receiver 1 may be generated by a profile management function II. and sent to the receiver I by a proffle data transmission function 12 at the head end 2. The scheduling function 8 may receive the viewing data 7 from the receivers I, and may he responsive to the viewing data 7 when scheduling substitutional and/or linear media items.

[0028] Figure 2 represents the steps performed in a method of scheduling, delivering and displaying one or more substitutional advertising campaigns, in an embodiment of the invention. Each substitutional advertising campaign may comprise one or more media items, sometimes referred to as copy' or copy items', each media item being associated with a viewer profile segment defined by segment data and/or one or more segment rules associated with that item. For example. an advertising campaign for a range of cars may comprise a set of media items, each comprising an advertisement for a particular car in the range, designed to appeal to a segment of the market defined by the associated segment data and/or rule.

[0029] ffi the present embodiment the profile data 5 of each broadcast receiver 1 comprises a set of profile data items stored locally at the receiver. Each receiver I also has a unique identity, such as a subscriber card number (Subscriber ID) stored on a smart card accessible by the receiver 1. The profile management system II accesses a database of subscriber details 13 associated with the unique subscriber identities, including subscriber details provided when subscribing to the broadcast service, subscriber preferences provided via the receiver I or other communications link, and/or third party data which the subscriber has allowed to be used for this purpose. Hence, the database 13 stores a wealth of profile data items, which may be used to define profile data and/or campaign segments. However, it would not he practicable for each broadcast receiver I to replicate all of its associated data items in the profile database 13, so as to he able to make a comparison with thc segment data of any particular campaign. Moreover, a prcdcfincd, fixed set of profile data items may require excessive processing by the receiver to identify whether the receiver I belongs to a particular segment. For example, a predefined profile data item may comprise a truncated postcode (used for example to determine a channel set -e.g. a bouquet or sub-bouquet -which the receiver I is enabled to rnceive), while a segment may be defined by a much larger region. To determine whether the truncated postcode coresponds to a particular region, the receiver I would need to obtain a list of truncated posteodes corresponding to each region. and compare its truncated postcode with the list of the postcodes.

[0030] histead, in a profile generation step Sl. profile data items are generated from the profile database 13 for use in one or more specific campaigns. For example, a campaign may include different media items for viewers in the North and South of England, so a campaign-specific profile data item may indicate whether a given subscriber is located in the North or South of England. The profile management function 11 interrogates the profile database 13 and determines a campaign-specific profile datum for each subscriber ID intended to receive the corresponding campaign. In this way. the proffle data items stored on the profile database 13 may be used flexibly to define the segments for a specific campaign, without requiring a large quantity of profile data to be broadcast to or stored at the receiver I. [0031] The profile data may comprise a discrete set of profile data for each campaign.

and/or general profile data that is not specific to a particular campaign. For example, the general profile data may comprise data likely to be of general use in defining segments.

such as gender, age range, location, socio-economic oup etc. This general profile data need only he updated occasionally, whfle campaign-specific data should he updated as new campaigns are introduced.

[0032] Also in the profile generation step S 1, campaign metadata are compiled.

compnsing: * For each campaign, a campaign ID and a list of segments * For each segment, a segmentation rule and a media item identifier * For each copy identifier, location information indicating where in the broadcast stream the media item is located [0033] In steps S2 and S3. the updated profile data items and the campaign metadata are acquired by the receivers 1 in advance of the substitutional slots to which the campaign metadata relate. Note that the order in which steps S2 and S3 are performed is not important. The updated profile data and campaign inctadata may be transmitted periodically on one or more channels separate from programming channels and hidden from users of the receiver 1, and to which each receiver 1 may tune periodically, such as once a week. The prolile data items may he portioned into blocks according to subscriber ID, so that the receiver 1 need only receive the block relevant to its subscriber ID, thus reducing the time for which the receiver 1 need be tuned to the hidden channel.

[0034] At step 52, each receiver 1 acquires its corresponding updated profile data items and updates its locally stored profile data accordingly. The campaign specific profile data may be broadcast in encrypted form such that only the receiver 1 having the associated subscnber ID may decode the corresponding campaign-specific profile data item(s), for example using a key stored on the smart card.

[00351 At step S3, each receiver 1 acquires and stores the campaign metadata, and builds a substitutional copy list for itself by the following process, as shown in Figure 3. For each campaign (step Rl), the receiver 1 considers each segment in turn (R2). parses the associated segmentation rule, and attempts to match the segmentation rule with its stored profile data (R3). If a match is found, then the media item identifier for that segment is recorded in the substitutional copy list (R4) and the receiver 1 moves to the next campaign (RO); otherwise, the receiver I considers the next segment (R5) .Since (lie receiver I can only output one substitutional media item at most per substitutional slot, it is not necessary to consider other segments in a campaign once a match is found.

[0036] The segmentation rule and profile data may be defined in many different ways. lii one embodiment., campaign-specific profile data may simply indicate into which segment the associated receiver I has been categorised. The segmentation rule then merely requires the receiver 1 to match its previously indicated segment with one of the segments in the campaign metadata. In another embodiment, each segmentation rule may be expressed as a combination of different profile data items, which may not be campaign-specific, for

example:

IF (GENDER = Male) and (REGION= Borders or Scotland) then SEGMENT=1 IF (GENDER = Female) and (REGION= Borders or Scotland) then SEGMENT=2 and so on.

[0037] Alternatively, the profile data could be dispensed with altogether and the campaign metadata could explicitly identify the receivers belonging to each segment. hi that case, profiling is perfoimed internally at the profile management function 11.

[0038] lii a media content delivery step S4, each receiver 1 acquires the media items identified in the substitutional copy list. The media items may he stored in a partition of a local hard disc, for example. If an identified media item is already stored locally, it may be removed from the substitutional copy list and need not. be acquired.

[0939] In an alternative embodiment. each receiver I may acquire and store all of the niedia items for a campaign, and niay select one of the media items for output based on a later comparison of the associated profile data with the segment definitions for that campaign. This alternative is more wastelul ol local storage, hut allows the order of steps S2 and S3 to be reversed.

[0040] Tn a scheduling step S4, the scheduling function schedules the substitutional campaign into the broadcast schedule, as described in detail below, Tn outline, this step generates a substitutional schedule indicating which substitutional campaigns can be shown in which substitutional slot in a broadcast schedule. Each substitutional slot is defined by a splice point indicating the frame-specific timing of the start and/or end of the substitutional slot in a particular broadcast channel.

[0041] At this stage, automation events are booked into the broadcast schedule as metadata in the substitutional slot to enable the encoders of the programme broadcast function 10 to generate the sphee point messages and perform any stream conditioning necessary to aid splicing at the receivers I. Additional automation events may be booked into the broadcast schedule at or before the start of each programme break containing substitutional slots to allow the substitution options to be communicated to the receivers 1.

[0042] At a play out step S5, a booked automation event (or alternatively an event generated by the automation function generated using a substitutional slot thok-ahead) causes the programme broadcast function 10 to broadcast, in a trigger track associated with a broadcast channel, a substitutional break schedule comprising a list of campaign IDs for each substitutional slot. The receivers 1 tuned to that channel receive and process the substitutional break schedule in order to determine for each substitutional slot whether to insert one of the locally stored media items in place of a linear media item included in the broadcast channel. Optionally. each media item may comprise a plurality of versions (e.g. standard or high definition) of die same content, and die receiver I may select one of the versions for output, for example based on an output mode (e.g. standard or high definition). Media items are cued by the receiver 1 for output at the defined splice points in the broadcast channel. The automation function next generates a splice point trigger at the point indicated by the substitutional slot which is then relayed to the cncoder and used to signal the receiver and condition the output stream for splicing. The splice points may be defined as splice events within the broadcast channel, using for example the SCTE 35 standard. When the receiver 1 receives the splice event, it outputs the locally stored media item corresponding to the campaign ID in the substitutional break schedule, if available, in place of the live broadcast stream. At the end of the substitutional slot(s), indicated by the duration of the splice event or by a further splice event, the output of the receiver 1 reverts to the live broadcast stream.

[0043] In an update step Sb. the receiver I may delete stored media items which are no longer required. for example which no longer match the stored profile data after the latter is updated. or for which the associated campaign has expired. The receiver 1 may also delete campaign-specific profile data items and/or campaign metadata associated with an expired campaign. Alternatively, previous versions of at least. profile data and campaign metadata may be stored at the receiver 1 for reporting or diagnostic purposes.

[0044] The receiver I may update a counter associated with a specific campaign if a media item associated with that campaign has been output. The receiver may update a counter associated with respective individual media items, when that media item is output.

The receiver I may transmit the viewing data 7 associated with a particular campaign to the profile management function II, where the database 13 may he updated with the viewing data 7.

Campaign Attributes [0045] lii both substitutional and linear scheduling, a particular campaign may have some or all of the following attributes: Demographic -The target audience of the campaign Campaign targets Centre break ratio -the proportion of advertising media items to be shown in a break within a broadcast programme, rail er than heiween broadcast programmes Position in break Top-tail -the number or proportion of slots at the start and end of a break (considered more desirable than the middle of the break) Target ratings Strike weight -a measure of how the frequency of display of the campaign varies over time Universe -the number of individuals in the demographic being targeted by the campaign Clash Code -a category code used to implement restrictions imposed by regulators as to how advertisements may be placed together in a schedule (e.g. alcohol and car-related advertisements are not to be shown in the same break).

One or more reporting categories -code for the product type(s) being advertised; these do not restrict scheduling hut are used for reporting purposes.

[0046] The programming schedule itself may include the following attributes: Restriction codes (by time) -e.g. codes that indicate time restrictions for certain types of advertisement, such as a watershed Cast List -the list of cast members appearing in a broadcast. programme [00471 lii addition, an individual copy (i.e. media) item for a particular campaign has its own set of attributes or metadata: Duration -i.e. the display length of the advertisement Clock number -a unique identifier for the media item Restriction codes -a media item for a campaign has a set of restriction codes, which may be defined only after the booking stage. The codes define properties of the content of the media item which may restrict the scheduling of the media item, such as the type of product or service being advertised, the minimum age of viewer or the watershed after which the media item may be shown.

Cast list -the list of cast members appearing in the media item. Regulations may stipulate that there should be no overlap between cast members in an advertisement break and cast members on the preceding and/or foflowing programme. so that cast list attributes should be specified for each advertising media item.

[0048] Figure 4a shows the main entity relationships between the attributes and the campaign and campaign copy (i.e. media items), in a non-aggregated campaign. The clash code has a one-to-one relationship with the campaign as a whole, while the campaign target and reporting category have many-to-one relationships with the campaign as a whole. The campaign may have a one-to-one relationship with a product category, through which the relationship with the clash code and reporting category is acquired.

Individual copy items have a many-to-one relationship with the campaign as a whole; in other words. each campaign may have one or more associated copy items. Cast Members, Restriction Codes and Presentation Codes each have a many-to-one relationship with an individual copy item.

[0049] Hence, it can he seen that a campaign comprises a set of media items, with some attributes (campaign target, clash code, reporting category) associated with the set as a whole, while other attributes (east. member, restriction code, presentation code) are associated with individual media items (or subsets of media items) within the set.

[0050] Different substitutional variants may be used, based on the number of campaigns and copy variants of those campaigns schedukd in a slot in a programme schedule. Each slot contains a linear media item that is included within the broadcast channel, for output by receivers for which substitution is not enabled, or for which the profile data is not addressed by any of the segments.

[0051] Figure 5 shows a first variant. referred to as Single Advertiser Multiple Copy (SAMC), in which the slot S is scheduled to contain a linear media item L and multiple substitutional media items from a single campaign C. The segment data Segi. Seg2, Seg3 for each substitutional media item defines the segment addressed by that item.

[0052] Figure 6 shows a second variant, referred to as Multiple Advertiser Single Copy (MASC), in which the slot S is scheduled to contain a linear media item L and multiple substitutional media items, each media item being from a different campaign Cl, C2, C3.

The segment data SegA, SegB, SegC for each media item defines a segment addressed by that item, but the segments from different campaigns may be defined in terms of different profile data items or segment rules; this raises the possibility that the segments may overlap, so that some receivers cannot determine which copy to output, based on a comparison with their profile data.

[0053] Tn a further variant, referred to as Multiple Advertiser Multiple Copy (MAMC), the slot is scheduled to contain substitutional copy from multiple campaigns, with more than one of the media items belonging to the same campaign, and addressed to different segments. Hence. MAMC is ahybrid between SAMC and MASC.

Scheduling [0054] Scheduling may need to be performed in two stages: 1. Booking -placement of campaigns within a broadcast schedule that is known in advance. Booking may he performed sequentially. as campaigns are made available for scheduling.

2. Pre-transmission checking -checking immediately before broadcast that the scheduled campaign media items meet the required constraints with reference to the final version of the schedule immediately prior to transmission.

Pre-transmission checking is necessary as an additional step to booking, because the broadcast programmes may have changed from the advance broadcast schedule. For example, the broadcast timing may have changed due to overruns or newsilashes, or the programme content may have changed, or may he known to include material such as news items that may clash with particular content in a media item.

[00551 The scheduling of advertisement campaigns, based on the attributes or mctadata listed above, is a combination of two formal classes of mathematical and computational problem, namely constraint satisfaction and optimization. Booking involves constraint satisfaction based on attributes of the schedule and of campaigns within a break, and optimization based on the campaign targets of the different campaigns. Pre-transmission checking involves constraint satisfaction based on attributes of the programming schedule and the media items booked within a specific break.

[0056] Examples of these constraints include: Booking constraints * The duration of the slot within the break should meet or exceed the duration of the media item * The clash codes for the campaign should not clash with the time-based restriction codes for the schedule * The clash codes for the campaign should not clash with other clash codes for other campaigns contained within the break Booking optimisations * The booking of a slot should make efficient use of the demographic inventory within the schedule; in other words, the predicted demographic profile of viewers of a slot within the schedule should match as closely as possible target demographic of campaigns booked with that slot.

* The booking of the slot should contribute to campaign targets such as ratings and campaign delivery ratios (centre-end break, position in break, strike weight etc.) Pre-transmission checking constraints * The media item should not contain any cast members in common with adjacent (preceding or following) programmes * The restriction codes apphed to the media item should he compatible with the contents of the programming, the break. and the time of day [0057] In linear scheduling, the above constraint satisfaction and optimization problems require substantial computational resources, particularly in the case where time-critical re-scheduling is needed during the prc-transmission check.

[00581 Substitutional advertising introduces multiple alternative media items, potentially from multiple different campaigns. within the same substitutional slot within a break.

Substitutional advertising gives rise to additional complications, as follows: Additional booking constraints * The duration of the slot within the break should meet or exceed the duration of each media item scheduled to that slot.

* The durations of the substitutional media items within a slot should all be the same (or at least add up to the same duration; for example, two or more shorter media items may he booked sequentially within a s'ot provided that the total duration of the sequential media items is equal to the duration of the slot.

* Clash code checks against the schedule should be applied across all the substitutional vanants of the substitutional slot.

* Clash code cheeks between media items within the break should be applied across all the substitutional variants of the substitutional slots. This can potentially include all the variants of additional substitutional slots within the break.

Additional booking optimisations * The bookings of all the substitutional media items within a substitutional slot should make efficient use of the demographic inventory within the schedule.

* The booking of all the substitutional media items within a substitutional slot should contribute to their respective campaign targets such as ratings and campaign delivery ratios (centre-end break, position in break, strike weight etc).

Additional pre-transmission constraints * No substitutional media items may have east members in common with the preceding programming.

* The restrction codes applied to all of the substitutional variants should be compatible with the contents of the programming, the break, and the time of day.

taking into consideration that there may be more than one substitutional slot within a break.

[00591 These additional requirements have the effect of increasing significantly the number of eaculations that need to he performed to ensure that the scheduled contents of a break are compliant with the relevant constraints and optimisations. These calculations need to be perfoimed every time a booking is performed, and also as part of pre-transmission checking.

[00601 Consider an example of a break containing 5 slots, two of which are substitutional slots. The iirst substitutional slot contains a SAMC campaign with 3 substitutional options. The second substitutional slot contains three MASC campaigns along with the linear campaign. This gives the following break makeup: * 5 slots in the break * 8 campaigns in the break * 11 media items in the break * 20 copy variants of the break [0061] During hooking. only campaign compliance is considered. which gives rise to a processing uplift of 5/8 or 60%. During pre-transmission checking. copy compliance should also he performed. If compliance is performed as if all the media items are shown together, this gives rise to a processing uplift of 6/Sths or 120%. However this simplification introduces the limitation that campaigns with the same clash code cannot share the same substitutional slot even thought the effect the clash codes are meant to prevent (e.g. two campaigns with the same clash code being shown in the same break) could never occur. A more correct approach would be to consider all the copy variants in turn which, even without optimization. would increase processing by 20 times in the

above example.

Aggregation [0062] Tn a first embodiment of the invention, at least some of the above problems are overcome by a process in which the complexity of the substitutional model is reduced substantially to that of the conventional linear model. The present inventors have observed that the attributes belonging to a single campaign and its associated copy items, and the relationships this campaign and copy items have with programming and other copy items within a break are broadly similar regardless of whether a single campaign/copy item combination or an aggregate of many campaigns and many copy items are considered.

Referring to the entity-relationship diagram of Figure 4b, if the Campaign entity is replaced with an Aggregate campaign and the Campaign copy item with multiple Campaign copy items, then the only change that would need to occur is that the relationship between Campaigns and Clash code would change from "one to one" to "one to many". All other relationships would remain the same. This shows that an aggregation scheme may allow substitutional advertising to be scheduled in a similar manner to standard linear advertising.

[0063] In an aggregation scheme, multiple substitutional media items are treated as a single aggregate for the purposes of booking into a linear schedule. In other words, attributes that are specific to individual media items, or to a subset of the media items, are aggregated together and die aggregated attributes are treated as having a many-to-one relationship with a single aggregated Campaigns entity, referred to as an aggregate campaign. The aggregate campaign is then booked into the schedule by applying the constraints and/or optimisations to the aggregated attributes.

[0064] The aggregation scheme will now be explained in more detail, with reference to Figure 7. An aggregate campaign A is composed of a single linear media item L and a single "pod" P which in turn contains one or more substitutional media items belonging to different campaigns Cl, C2. C3. The media items are selected so that the user segments SegA, SegB, SegC of media items within a pod do not overlap; this means that a given speci lie user profile will fall within one of die user segments. at most.

[0065] Attributes of the constituent media items of the aggregate campaign A (including hooking constraints and campaign targets) are aggregated together and the aggregate campaign is scheduled using the aggregate set of attributes as if they were a single set of attributes for a single campaign. In a similar manner, an aggregate campaign A comprises individual media items for each of the campaigns in the aggregate. The schedule includes a set of aggregate slots, into which aggregate campaigns may be scheduled.

[0066] Pods P are formed by grouping compatible substitutional campaigns Cl. C2. C3 together. Substitutional campaign compatibility is assessed according to the foflowing factors: * Campaign segment overlap * Target demographic * Campaign duration * Media item length [0067] Each pod P is assigned a unique identifier. Note that the same substitutional campaign can he associated with more than one pod P. [0068] Each pod P is grouped with a linear campaign L to form an aggregate campaign A. Each aggregate campaign A is also assigned a unique identifier. Note that the same pod P may be grouped with more than one linear campaign L. to foim a corresponding plurality of aggregate campaigns A. [0069] Campaign targets of the constituent items of the aggregate campaign may be aggregated into a single set ol campaign targets which become the campaign targets ol that aggregate campaign A. Alternatively, campaigns niay be selected for inclusion together in a pod P on the basis of compatible campaign targets.

[0070] Aggregating attributes may give rise to a constraint being applied unnecessarily.

such that the aggregate campaigns cannot he scheduled in a break. For example: * Aggregate campaign Al is booked first into a s'ot in a break, and has a car clash code; * Aggregate campaign A2 also contains a ear clash code and is required to be booked into another slot in the same break.

[0071] Based on this information alone, campaign A2 cannot he booked into the break.

because a booking constraint prevents two media items having the same clash code being shown in the same break. However, additional information is available about the decomposition of the aggregate campaigns in question: * Campaign Al selects a campaign Cl for a ear from a first manufacturer if the subscriber is in the London region * Campaign A2 select a campaign C2 for a car from a second manufacturer if the subscriber is in the Border region [0072] Hence, if the segments of campaigns Al and A2 are taken into account, it. is apparent that campaign Al and campaign A2 cannot both select a car advertisement for a given subscriber, since the segments ol the two ear campaigns do not overlap: a subscriber cannot be both in London and the Border region.

[0073] As a solution to this problem, in the case of a clash rule being invoked between two aggregate campaigns. the aggregation function may communicate to the scheduling function whether the clash is reconcflable e.g. because the segments between the two campaigns do not overlap where there is a clash rule invoked. This communication may either occur in real-time or the booking could be allowed and marked as having a warning status and an asynchronous process may query the aggregation function for all bookings with a warning status and prevent booking where the aggregation function indicates that the clash is irreconcilable.

[00741 The use of aggregate campaigns, each having the aggregated attrbutes of the multiple substitutional campaigns contained therein, addresses the additional booking and pre-transmission checking constraints of a substitutional system, without requiring significant changes to a linear scheduling system, and with offly a modest increase in processing complexity. This holds true regardless of the number of segments and substitutional options contained within a pod P. Separate Booking [0075] lii a second embodiment, one or more linear media items may be booked into an available slot, separately from the substitutional media items, and preferably before any substitutional media items arc hooked into that slot. The booking of linear media items may be performed using conventional booking techniques. However, it is then preferable to indicate for each slot what kind of substitutional media items can be booked into that slot; this indication comprises so-called avail schedule' data which is generated and may he updated during hooking.

[0076] The avail schedule data may be based on one or more predetermined substitutional rules ol the host campaign, In which lie linear media item belongs. For examp'e, ii the host campaign targets "adults" then allow substitutional avails to top-slice high income households) [00771 The avail schedule data may indicate constraints on substitutional media items that can be booked into the break as a whole, such as: * clash codes relating to proammes before and/or after the break * clash codes relating to media items booked into other slots within the break (e.g. ii a car advertisement is already hooked into the break, do not hook an alcohol advertisement into an avail) * compliance codes relating to watershed and I-IFSS (high fat sugar and salt) exclusions [0078] The avail schedule data may also indicate constraints on substitutional media items that can he hooked into a specific slot within the break, such as: * slot length, determined by length of linear media item hooked into that slot * single/multiple advertiser: indicates whether the suhstitutional media items may be from a different advertiser from that of the linear media item * segment exclusions: defines which segments are not available for substitutional advertising, for example because they have already been allocated within that slot.

[00791 The substitutional media items for each slot may be booked as an aggregate pod P as in die first embodiment. Alternatively, the substitutional media items may he booked individually, in which case the segment exclusions for that slot are updated as the bookings are made.

[0080] Overlapping segments between the different media items booked into each slot are resolved according to a predetermined rule, so that the segments no longer overlap. For example. priority may be given in order of booking; hence, in the example above, the segment of the first substitutional media item is (ABC1 NOT London). If a second substitutional media item, booked subsequently, is targeted at households with children.

the actual segment for that item is (children NOT ABCI NOT London).

[0081] In an alternative rule, although the linear media item is booked first, it is given lower priority than any substitutional media items booked subsequently. and the substitutional media items are given priority in order of hooking. In that ease, the segments would be: * Linear item: London not ABC 1 not children * 2 substitutional item: children not ABC1 [0082] Other segment priority rules may be used within the scope of the invention. For example, subsequent bookings within a slot may be prevented if the associated segment overlaps with any ol the segments already hooked into that stht. However, such a rule would require standardization of segment definitions so that overlap can be automatically determined, which reduces the flexibility of the booking system.

[00831 An advantage of the second embodiment is that bookings can be confirmed as they are requested, rather than requiring hooking requests to he held until aggregate booking can be performed. as in the first embodiment.

[0084] lii a development of the second embodiment, the avail schedule data for a specific slot may include one or more clash codes relating to media items already booked in other slots within the same break. For example, if an alcohol-related media item has been booked into another slot within the break, such as a linear or substitutional slot, an alcohol' clash code may be included in the avail schedule for the specific slot. A predetermined clash code rule then prevents a media item with a car' clash code from being booked into the specific slot, to prevent the possibility of car and alcohol-related media items being shown in the same slot.

Fractional Slot Durations [00851 The scheduling of fractional media items having a duration that is a fraction (such as one half) of that of a substitutional slot creates additional constraints in that one fractional media item should be matched with one or more other fractional media items and scheduled sequentially so as to make up the duration of one substitutional slot. In one solution, fractional media items are concatenated together to form a concatenated media item having the aggregated attributes of the constituent media items, and the concatenated media item is then treated as a single media item with the aggregated attributes for the purpose of scheduling.

[00861 Tn another solution, the fractional media items are scheduled into an aggregate campaign, and the substitutional schedule broadcast to (he receiver indicates that the fractional media items are to shown sequentially rather than as alternatives. For example.

[he schedule may indicate lie lollowing suhslilu[ional options: 2. substitutional campaigns 1111 and 2222 in sequence In this solution, concatenation of the fractional media items need not be performed prior to scheduling, but the need to schedule fractional media items in sequence creates additional constraints that should be resolved by the booking system.

[00871 Tn the embodiment described above, it is assumed that once a campaign or aggregate campaign is scheduled to a slot, any ol the substitutional options may he selected by one or more receivers, since the scheduling constraints have been satisfied. In an alternative embodiment, one or more substitutional options with a campaign or aggregate campaign may be selectively disabled at or just before the time of broadcast, for example by means of modification of the substitutional schedule. This selective disablement may be used to control the frequency with which each substitutional option is displayed. The substitutional options to be disabled may be varied during a campaign. so that the delivery of certain substitutional options may be balanced with the need for rescheduling.

[0088] This technique could be applied to a linear scheduling scheme, in which a scheduled campaign delines an inventory of possible media items br a stht, and die linear item for that slot is selected from the inventory of possible items.

[0089] If the same substitutional campaign (including an aggregate campaign) is scheduled in multiple substitutional slots, with the same associated campaign metadata and profile data, a specific receiver 1 will deterministically select the same substitutional option each time the campaign is scheduled. In some cases, it maybe desirahk to vary the substitutional option for a specific receiver each time a campaign is scheduled.

[0090] lii one embodiment, each media item may comprise a sequence of clips, with one clip of the sequence being selected in turn for output by the receiver every time the associated media item is selected for output. This embodiment is particularly advantageous for delivery of media items having a total length that is greater than that of a substitulional slot, and enables delivery of a series withoul the need o schedule each clip of the series in a different, sequential campaign.

Recording & Playback [0091] The above embodiments have been described mainly with reference to live viewing of broadcast programming, with insertion of substitutional media items into the displayed live broadcast stream. hi one embodiment where the received broadcast stream is recorded locally by the receiver 1. such as a PVR, the inserted substituüonal items may be recorded within the recording of the received broadcast stream, so that the displayed content on playback is identical to that seen when watching the live broadcast stream with any inserted substitutional media items. This embodiment is advantageous in that the user may see on playback exactly the same content as was seen when viewing the broadcast stream live. It should be noted, however, that the above embodiments do not. require the broadcast stream to he viewed live; instead, the stream could he recorded for later viewing, with substitutional media items being inserted into the recording.

[0092] hi an alternative embodiment, the recording may include data identifying the splice points and substitutional schedule, and media substitution may be performed on playback, provided the necessary campaign metadata, profile data and substitutional items are still available at the receiver; these items may be saved for the duration that the associated recording is maintained at the receiver 1. This approach is more flexible, since any updates to the profile data, campaign metadata and/or substitutional items may he taken into account whcn selecting a substitutional itcm for playback. Howcvcr. thc user experience is different from conventional recording, in which the user expects to see on playback the same content that was previously viewed live.

[0093] Similar approaches may he applied to a PVOD (Push Video on Demand) system.

in which broadcast programmes are recorded automatically without specific selection by the user, as described for example in WO-A-06/l2597l.

Reporting [0094] It is also important. to determine, or at least reliably estimate, the ratings of each campaign, in other words how many times the campaign has actually been displayed, and optiona'ly. to how many viewers of the target demographic profile of the campaign. In a conventional linear advertising model, survey evidence is used to estimate the viewing figures for each channel at a particular lime, and the ralings for a parlicular campaign are derived from those figures. In a substitutional advertising model, additional information is needed to apportion those figures to each of the substitutional options within a slot 5, particularly if one substitutional slot contains options from different campaigns.

[0095] Since the segments of each of the campaigns within a pod P do not overlap, the selection of the campaign to be output for each slot by the receiver 1 is deterministic.

given the profile data stored in each receiver I. It is therefore possible to determine or at least estimate the rating of each campaign, without detecting which campaigns have been output by a particular receiver 1. Instead, all that is necessary is to determine or estimate the number of receivers 1 tuned to each broadcast channel, and the profile data of those receivers. In one example, viewing data 7 comprising data sets of the form [Subscriber ID]. [Channel], [Time of Day] is sufficient; this data may be collected by the profile management function I I and combined with information from the aggregation function to determine which campaigns would have been output by each receiver. This viewing data may he reported through return channels from the receivers I. or obtained from survey evidence. In this way, the amount of data to be collected is minimised, and the accuracy of reporting improved.

Splicing Architecture [0096] As described ahove, in response to a splice event, the receiver outputs a locally stored substitutional media item at a splice point defined as a splice event in a broadcast or playback stream. Architectures that enable transport stream level splicing at the receiver 1 will now be described.

[0097] In a first embodiment shown in Figure 8, data is parsed at transport stream eveI, time stamp information is modified, am! the modified transport streams are reinjected into a demultiplcxer 20. The demultiplexer 20 is of a conventional architecture in which a demodulated audiovisual transport stream 14 is provided to a demultiplexer input 21 and demultiplcxcd into data 22, such as Teletext data, a video packctized elementary stream (PES) 26 and an audio PES 27, for output to middleware 30, video decoder 31 and audio decoder 32 respectivdy. The demultiplexer 20 also outputs a video time stamp (TS) 23 and an audio TS 24, parsed from the transport stream 14.

[0098] Tn the first embodiment, the video and audio TS 23, 24 are input to a PTS trigger 33 which detects a discontinuity in the TS 23, 24, caused for example by splicing a subsitutional media item into the transport stream 14. If a discontinuity is detected, a substitute video and audio TS 35 are generated and adapted to the original TS references 34 to generate an adapted TS 36 which is continuous with the time references before the discontinuity. The adapted TS 36 are then reinjected to a TS input 25 so that the output video and audio PES 26, 27 have the adapted TS 36. In this way. the video and audio decoders 31 and 32 do not encounter the TS discontinuity.

[00991 In a second embodiment shown in Figure 9, the audio and video PES 26, 27 and processed between the dernultiplexer 20 and the audio/video encoders 31, 32. As a result.

the second embodiment is simpler than the first emhodiment and provides lower latency.

since die need br a second pass through the demultiplexer 20 is avoided.

[00100] In the second embodiment, the audio and video PES 26 and 27 are provided to the PTS trigger 33, which detects discontinuities in the TS contained within the PES in a similar fashion to the first embodiment. If a discontinuity is detected, substitute PES 35 are generated and an adapted PES 36 is created with TS references continuous with those of the PES 34 before the discontinuity. The adapted PES 36 is output to the video and audio decoders 31, 32.

[001011 In either embodiment, scrambled and/or encrypted transports streams 14 may need to be descrambled/decrypted at (he same stage as the demultiplexer 20, so that the TS can be parsed and modified.

Splicing Point Selection [001021 In an embodiment of the invention, splicing points are defined with reference to the presentation time stamps (PTS) that are required for audio/video synchronization and are common to the audio and video streams of a particular input (e.g. broadcast or playback) stream. Thus, a single splicing point can be defined for both audio and video using the same reference.

[00103] To avoid decoding problems with interframe coded video, the splicing points are defined so that there arc no intcrframe references across a splice point; for example, there are no forward references before a splice point and no backward references after a splice poiut. Preferably, splice points are defined between groups of frames where there are no references between groups, such as at the beginning ol an 1-frame (an independent frame) in a Group of Pictures (GOP) in MPEG-2.

[00104] Each suhslilu[ional media item is encoded independently, so does not contain any interframe references outside itself. Thus, au MPEG-2 encoded substitutional media item will contain one or more complete GOPs and will start with an I-frame.

[001051 In one embodiment, splice points are selected at the head end 2, and transmitted by the proamme broadcast function 10. An advantage of this approach is that the receiver 1 does not need to parse an MPEG stream, for example to suspend MPEG decoding until the start of the next GOP.

[001061 Each GOP is preferably encapsulated within exactly one PES packet. This ensures that a splice point always occurs at the beginning of a GOP: the PTS value is placed in a PES packet header, which therefore indicates the beginniug of a GOP. An additional advantage is that a Payload Unit Start Indicator (PUSI) bit in the transport stream header can be used to parse the stream so as to identify the beginning of a GOP, without having to read the frame type from the Elementary Stream level, thus reducing the level of processing resource required. As shown in Figure 10, a splice point SP is defined at the beginning of an I frame of an encoded input video stream Ely. An encoded substitutional video stream ESV is spliced in at that point, also beginning with an I frame.

The resultant encoded output video stream EOV comprises the frames of the encoded input video stream EIV up to the splice point SP, and the frames of the encoded substitutional video ESV after the splice point SP. The decoded output. video stream DOV is delayed from the encoded output video stream EOV because of decoding latency. so that the timing of the splice point SP' in the decoded output video DOV is delayed relative to the indicated splice point SP.

[001071 In an alternative embodiment, each PES packet contains a single video frame, so each frame has its own PTS. This allows a splice point to he defined at any frame within a GOP. hut the splice point must he selected so that decoding is not disrupted across the splice point. For example. a splice-in point may be defined after a P frame in the encoded input video Ely, since the P-frame encoding only depends on previous frames. Figure 11 shows an example similar to that of Figure 10. but with the splice point within a GOP.

[001081 A splice-out point should preferably be defined at a GOP boundary; otherwise, the receiver 1 would need to delay the splice-out until the next GOP in the encoded input video EIV; this could lead to a gap or frozen frame from the end of the substitutional video for a short period of time -up to half a second for MPEG2 encoding, or potentially several seconds for H.264. This would also require the receiver 1 to parse the output encoded video stream EOV to identify a GOP start point, which is undesirable because of the need for additional processing resources at the receiver 1, and the need to customize the receiver platform at a hardware/driver level.

[001091 Preferably, the following requirements should be met at the head end 9 to ensure seamless splicing: * the first frame of the input encoded video EIV after the splice-in point should be an I-frame * the first frame of the input encoded video EIV alter the splice-in point should he placed at the beginning of a new PES packet. and contain a PTS value * the first frame of the input encoded video EIV after the splice-out point should be an I-frame * the first frame of the input encoded video EIV after the splice-out point should be placed at the beginning of a new PES packet, and contain a PTS value * the input encoded video stream EIV should used closed GOPs i.e. the frames of one GOP do not reference any frame of another GOP * the last frame of the encoded substitutional video must not reference a future frame i.e. for MPEG2. it must be a P-frame or I-frame * the length of the encoded substitutional video ESV must be equal to the interval between the splice-in and splice-out points [00110] If any of the above requirements is not met, splicing is still possible but may not be seamless. The following effects may be visible to the user: * freezing of last frame of the output video for up to a full GOP length at the beginning and/or end of the splicing interval.

* up to a full GOP of substitutional video might be dropped at the beginning and/or end of the splicing interval.

* up to a full GOP of unselected content might be visible at the beginning andlor end of the splicing interval.

If there are multiple adjacent splicing intervals, these problems maybe compounded.

[001111 Although the above embodiments have been exemplified with reference to MPEG-2 video encoding. aspects of the invention are applicable to other video encoding formats, such as H.264.

Audio Splicing [00112] A particular problem may occur with decoding ol the audio stream, in that the audio decoder 32 may not be managed within the receiver 1. but instead by an external amplifier ignorant of when any splicing may occur in the audio stream it receives. It is therefore desirable to ensure that the audio frame rate and synchronization remains continuous at the output to an external audio decoder 32 during substitution, to avoid any problems caused by the external amplifier receiving out-of-sync frames.

[001131 Figure 12 illustrates a broadcast stream BS comprising audio and video packet elementary streams 26, 27, comprising packets including presentation time stamps (PTS) indicating the time at which the contents are to he presented. for example as output by the receiver 1, and splice insert messages VSS (video splice start) and VSE (Video Splice End). The actual timing of the video splice points is indicated as SPI (Splice Point In) and SPO (Splice Point Out). Figure 12 also illustrates the corresponding receiver output RO, comprising audio and video frames.

[00114] One problem stems from the fact that video frame and audio frame length do not align: each video frame covers a period of 40 ms for example, while an AC3 audio frame carries audio samples for a period of up to 32 ms. This means that the PTS value referencing the actual video splice point in an splicing message will not exactly match the PTS value of the PES carrying the AC-3 frame in the stream in which the splice will be applied.

[00115] To overcome this problem, the receiver 1 determines the actual PTS value of the related audio frame having a PTS value equal to, or the smallest value greater than, the video PTS value for the video splice start and end VSS, VSE. Normally, an audio frame comes later than the associated video frame in the transport stream; this audio frame is therefore monitored in the live transport stream, past the video splice point PES, especially for a splicing from live to playback, to determine the audio splice point.

[00116] It is possible that the point when the PES for the last component appears in the stream is too dose to the presentation time where the substitution must start, not leaving enough time for the receiver 1 to operate the substitution on time. The receiver 1 may then switch from the broadcast stream earlier and miss outputting one or more broadcast frames, as shown in Figure 12. In that case, the receiver 1 will have to ensure it maintains a consistent audio frame rate in compensating the exact number ol missing frames at the receiver output. by generating mute frames locally, before the substitution starts.

[00117] Similarly, the receiver I may output locally generated mute frames before an audio splice-out point, if the spliced-in content finishes before the indicated audio splice-out point. A muted audio output is preferable to problems that may be caused by unsynchronized audio.

[00118] The actual size of the mute frame will be fixed, based on the audio sampling rate parameter specified in the broadcast channel.

[00119] A further problem is that the misalignment between the video and the audio frames in the broadcast stream is likely not to be the same as that in the substitutional content. To overcome this problem, the audio frame timing of the substitutional content output to the audio decoder is aligned with that of the broadcast stream. This may cause a synchronization error SE between the audio and video of the substitutional content during playback, since the timing of the audio frames has been shifted relative, hut this effect is preferable to the unknown errors that may he caused in external decoders by timing discontinuity.

Splice Point Signalling [00120] As discussed above with reference to Figure 1, the headend 2 includes a media broadcast function 9 which encodes media content for broadcast, based on scheduling information provided by a scheduling function 8. The media broadcast function 9 includes splice insert messages in the broadcast stream, which signal the precise video frame at which a splice point will occur, with reference to a frame timing indicated by the PTS for each frame. Each splice insert message is preferably inserted in the broadcast stream at a fixed interval before the occurrence of the splice point.

[00121] The timings of the sphce points are signaled to the media broadcast function 9 by the scheduling function 8, with rcfercncc to a common clock. However, the scheduling function 8 has no knowledge of the frame timing of the encoded frames output by the media broadcast function 5. The encoder must perform a conversion between (he reference to (he common clock made by (he scheduhng function to signal (he time when the splice point frame will he presented to the encoder and the frame timing that will be associated with the video splice point frame at the output of the encoder, but if the encoder is not properly synchronised to the common clock used by the scheduling function 9, the splice insert messages may refer to the start of a frame just before or just after the splice point timing signaled by the scheduling function. This can lead for example to one frame of a linear media item being displayed at receiver 1 before a substitutional media item is disp'ayed.

[00122] To overcome this problem, the frame timing of the encoder is synchronized with the clock refercncc of the scheduling function 8. This may require the scheduling function 8 to output a clock signal to the encoder for synchronization purposes, or alternatively both the scheduhng function 8 and (he encoder may he synchronized to a common clock reference.

[00123] For the case where the scheduling function 8 outputs a clock signal to the encoder, the method comprises inserting the UTC (Coordinated Universal Time) time at which the frame is played out and sent to the input of the encoder in the VITC (Vertical Interval Time Code) field of the frame. The encoder can then set a dock that accurately locates the time boundary at which each frame is received. The encoder will then be able to more properly calculate in advance the frame timing associated with any time reference in the future provided by the scheduling function.

Alternative Embodiments [00124] The above embodiment is described with reference to a broadcast system.

such as a satellite, cable or Internet broadcast system. Aspects of the invention are also applicable to a video on demand (VOD) or push video on demand (PVOD) system, in which a programme is received and/or displayed on demand, and includes one or more substitutional slots as part of the programme. The substitutional system may be applied to the substitutional system in a similar way to the broadcast system describcd above.

[00125] The above embodiment is described with reference to substitutional advertising, hut aspects of the invention are not dependent on the content or commercial nature of advertising. Substitutional systems as described above are applicable to other media types having other constraint and/or optimisation rules. For example, aspects of the invention are applicable to the distribution of programmes with substitutional segments.

br examp'e to allow disp'ay of alternative content depending on prolile data at the receiver. Tn that case, there may he constraint rules which restrict which combination of segments can be output. In another example. aspects of the invention are applicable to public service or system announcements targeted at particular user profiles.

[00126] The above embodiment discloses a video broadcast system in which broadcast programmes and substitutional media content comprise video, and associated audio where applicable. However, aspects of the invention are applicable to audio-only content, such as digital radio broadcasts, or a mixture of video and audio-only content: for example, the broadcast programmes may he video programmes, and the substitutional media content may comprise audio-only content that is output over a still picture generated locally at the receiver.

[00127] The above embodiment discloses a time-divided system in which the insertahle media items are output during breaks within or between programmes. However, the slots for insertable media items may he concurrent in time with programmes; for example, substitutional content may be superimposed on the display of a programme, or he added to or replace the audio output, for example for dubbing.

[00128] Alternative embodiments may he envisaged, which nevertheless fall within the scope of the following claims.

Claims (4)

1. Claims 1. A method of outputting an audiovisual substitutional media item within a media output stream at a media output device, wherein the media output stream comprises a video stream and an audio stream, and the media output stream includes a splice-in point and a splice-out point, the method comprising outputting dummy audio content subsequent to the audio content of the substitutional media item if the output of the audio content of the substitutional media item occurs before the splice-out point.
2. 2. The method of claim 1, wherein the dummy audio content comprises one or more audio frames synchronised with the audio stream of the media output stream.
3. 3. A computer program product comprising program code means arranged to perform the method of any preceding claim.
4. 4. Apparatus arranged to perform the method of any one of claims I to 2.