WO2010086021A1

WO2010086021A1 - Method and apparatus for efficient downstream video processing based on upstream metric processing and provision

Info

Publication number: WO2010086021A1
Application number: PCT/EP2009/051056
Authority: WO
Inventors: Anthony Richard Jones; Giles Wilson
Original assignee: Telefonaktiebolaget L M Ericsson (Publ)
Priority date: 2009-01-30
Filing date: 2009-01-30
Publication date: 2010-08-05

Abstract

There is provided a method of transmitting digital video comprising determining compression metrics about the digital video, and transmitting the compression metrics together with the digital video to which the metrics pertain. There is also provided an upstream centralised video pre-processor (220, 420) for use with an Internet Protocol based digital video transmission system, comprising at least one video feed input (110), a video pre-processor in communication with the at least one video feed input and adapted to provide video compression metrics information about the video feed and a compression metric and video feed transmitter, adapted to transmit the video compression metrics and video feed to at least one downstream video re-processor (430). There is also provided a downstream video re-processor (325) for use with the upstream video pre-processor and a system comprising both, and a method of receiving digital video.

Description

Method and apparatus for efficient downstream video processing based on upstream metric processing and provision

Technical Field

The invention is related to video coding in general, and in particular to a method and apparatus for processing video to provide video compression metrics for use by downstream video re-processors.

Background

Digital networks have been deployed for the distribution of video services for many years. The original simple broadcast model developed during the analogue era typically provides a service from a single source of transmission, e.g. a terrestrial high power transmitter, a satellite or a cable head end. This video transmission model supports the supply of an identical service to a very large number of receivers, and is shown in Fig. 1.

This traditional broadcast model has been augmented in recent years by more complex network topologies that allow enhanced services having greater flexibility and efficiency. For example, Broadband networks based on Optical Fibre (FTTH) or copper telephone lines (ADSL) have also been deployed that are able to offer interactivity as well as emulating the broadcast model. These so called IPTV (Internet Protocol Television) systems are exemplified in Fig. 2. The competitive pressure to enhance services among traditional network operators is now significant.

In networks such as satellite or cable TV, which have natural topologies that include processing stages between content sources and viewers, it is usual to import ready coded and compressed content streams from many sources and to select those services that are to be transmitted onward in newly constructed multiplexes. In broadband networks a similar process may occur between the main source servers and those placed nearer the edge of the network, i.e. the viewer; in this case the streamed services, typically Video on Demand (VOD), may be sourced elsewhere and thus imported from the original producers in real or non-real time.

In either case, the incoming video streams are often subject to a number of downstream re-processing stages at each major network node where the video and corresponding audio need to be tailored to the needs of the onward path. Typical processes that might be performed at the edge of the network (i.e. close to the viewer) are bit rate changing, re-multiplexing or re-encoding. Where these processes might alter the coding parameters they could be complex and there are implications for the integrity and quality of the resultant digital video stream(s) that must be addressed.

Furthermore, because these processes may be applied to a large number of services and occur near the network edges, it is necessary to simplify them in order to make the network edge unit implementation costs affordable. This is increasingly important as the processing point get nearer to the viewer, typically in the "last mile", because of the resultant increase in the number of re-processing instances required. Simplification on this scale may well lead to constraints in performance and a consequential loss of video quality by the time the recoded pictures reach the viewer.

This reduction in video quality must be avoided and so any method which allows the maintenance of coding quality whilst permitting low cost hardware and software implementation at the edge of network devices is to be welcomed.

Accordingly, the present invention proposes methods and apparatus whereby downstream video processing can be aided by means of assistance data embedded in or alongside the original source stream; this data provides information about the picture behaviour and details of up-stream coding, i.e. compression metrics, that would not be practical or cost effective to determine at the downstream stage, especially near the "last mile" point.

Summary Embodiments of the present invention provide a method of transmitting digital video comprising determining compression metrics about the digital video, and transmitting the compression metrics together with the digital video to which the metrics pertain.

Whilst the actual Quantization Parameter value used for a particular portion of digitial video is always carried as required by video compression standards, embodiments of the present invention include carriage of additional information (such as bit rate for alternative Qp values) that allows re-processing of the content without having to re- determine that information at every re-processing location, particularly the edge of network devices.

Optionally, the step of determining the compression metrics further comprises any one or more of: carrying out pre-processing analysis of a previously digitised video to determine the compression metrics used previously; gathering compression metrics used to digitise the digital video at a time of digitising; gathering compression metrics about the digital video while re-encoding or modifying the digital video content.

Optionally, the compression metrics are transmitted offset in time from the point in the digital video to which they pertain, such that the metrics arrive at a downstream re-processor before the video to which they pertain.

Optionally, the compression metrics and digital video to which the compression metrics pertain are incorporated into a single digital video stream.

Optionally, the method further comprises receiving the digital video at a remote location, and re-processing the digital video in accordance with an onward transmission requirement.

Optionally, where the digital video is to be carried over an Internet Protocol, Cable Television or Mobile Telephony based digital video transmission system, the method further comprises providing a central pre-processing device for carrying out the steps of determining the compression metrics, and transmitting said compression metrics together with the digital video to which they pertain, providing at least one edge of network video serving device for carrying out the steps of receiving the digital video at a remote location and re-processing the digital video in accordance with an onward transmission requirement, said at least one edge of network device including a compression metric buffer to receive said compression metrics, and a re-processor to re-reprocess the digital video.

Optionally, the system processes a plurality of digital input streams concurrently to provide a plurality of compression metrics about said digital input streams, and the method further comprises re-processing each digital video input stream according to the compression metrics of the plurality of digital input streams at the at least one edge of network digital video processing device. For example, taking a set of pre- processed metrics and deciding how to re-process the content of all of the respective video input streams to achieve a desired optimal performance for the group.

Optionally, the re-processing includes carrying out either recoding the digital video or changing the bit rate of the digital input streams.

Optionally, where a sub set of the plurality of digital input streams are each variable bit rate, and the re-processing comprises changing the bitrate of the digital input streams, the method further comprises combining the re-processed digital input streams to form a defined aggregate bit rate output stream profile. The defined aggregate bit rate profile may itself be time-varying, where it must compete with other data services using the fixed bit rate communications link to the user (for example, internet, VOIP, web, etc traffic).

Thus, embodiments of the invention allow a subset (likely a different subset) of the input streams to be re-processed at the edge. In normal operation, there is an expectation that multiple video feeds are to be pre-processed. Some of these may be recorded (e.g. VoD assets), whereas others may be live. These different source materials are then combined in differing ways at the re-processing node, according to the needs of a particular user or subset of users. The subset of re-processed input streams will then often need to fit in a fixed-size communications link, and could potentially share the fixed fixed-size communications link with other data traffic, in which case the overall sum of bit rates would need to vary to accommodate that other data traffic. Embodiments of the present invention also provide an upstream centralised video pre-processor for use with an Internet Protocol based digital video transmission system, a cable television system, or mobile telephony system comprising at least one video feed input (either live or stored), a video pre-processor in communication with the at least one video feed input and adapted to provide video compression metrics information about the video feed, and a compression metric and video feed transmitter, adapted to transmit the video compression metrics and video feed to at least one downstream video re-processor.

Optionally, the video pre-processor is adapted to provide information about stored video content.

Optionally, the video pre-processor is further adapted to provide the compression metrics by means of any one or more of: carrying out pre-processing analysis of the video feed to determine the compression metrics of previously compressed content; gathering compression metrics used to digitise the video feed at a time of compressing; gathering compression metrics about the video feed while re-encoding or modifying the video feed content.

Optionally, the compression metric and video feed transmitter is adapted to transmit the compression metrics offset in time from the point in the video feed to which they pertain.

Optionally, the compression metric and video feed transmitter is further adapted to incorporate the compression metrics and the video feed to which they pertain into a single output digital video feed.

Optionally, the compression metric and video feed transmitter is further adapted to transmit the compression metrics over a separate communication link from the video feed.

Optionally, the central pre-processor comprises a plurality of individual preprocessors operable as a single shared resource. Embodiments of the present invention also provide a downstream video re- processor, comprising a compression metric receiver, a compression metric storage buffer, and a video re-processor, adapted to re-process incoming digital video data according to compression metrics accompanying the digital video data previously received and stored in the compression metric buffer.

Optionally, the re-processor is adapted to re-process incoming digital video data by carrying out either recoding the digital video, or changing the bit rate of the digital video.

Optionally, where the incoming digital video comprises a plurality of variable bite rate input digital video streams, the re-processor is further adapted to re-process said input digital video streams to form a single constant bit rate output digital video stream.

Embodiments of the present invention also provide a system comprising at least one video input feed, an upstream centralised video pre-processor in communication with the at least one input video feed and adapted to provide video compression metric information about the input video feed or stored content, a compression metric and digital video transmitter, adapted to transmit the video compression metrics and the digital video to which the metrics pertain to at least one downstream video re- processor, and at least one remote video re-processor in communication with the compression metric and digital video transmitter. The downstream video re-processor may be of the aforementioned type.

Embodiments of the present invention also provide a method of reducing hardware requirements in an edge of network video serving device, comprising centrally preprocessing digital video input streams to determine compression metrics about said digital input streams, and providing the compression metrics to the edge of network video serving device by transmitting the compression metrics together with the digital input stream, where the transmission of the compression metrics removes a need for pre-processing hardware in the edge of network video serving device. Embodiments of the present invention still further provide a method of receiving digital video comprising receiving compression metrics together with the digital video to which the compression metrics pertain and using the compression metrics in further re-processing of the digital video.

Brief description of the drawings

A method and apparatus for efficient downstream video processing based on upstream metric processing and provision will now be described, by way of example only, and with reference to the accompanying drawings in which: Fig. 1 shows an overview schematic of a prior art analogue or digital

Television broadcast system;

Fig. 2 shows an overview schematic of a prior art Internet Protocol Digital Television multicast and/or unicast system;

Fig. 3 shows a schematic diagram of a prior art edge of network video re- processor;

Fig. 4 shows an overview schematic of an Internet Protocol Digital Television multicast and/or unicast system according to an embodiment of the present invention;

Fig. 5 shows a central processing platform device according to an embodiment of the present invention;

Fig. 6 shows an edge of network video re-processor according to an embodiment of the present invention;

Fig. 7 shows an overview flow diagram of a method of providing digital video according to an embodiment of the present invention; Fig. 8 shows a schematic diagram of how compression metrics may be sent from a central processing platform to an edge of network video re-processor according to an embodiment of the present invention.

Detailed description

An embodiment of the invention will now be described with reference to the accompanying drawings in which the same or similar parts or steps have been given the same or similar reference numerals. In Fig. 1 , which shows a typical digital TV broadcast system, a plurality of video source feeds 1 10 are provided to the broadcast television central video processing stage (e.g. a cable TV Head end), which provides a linear video feed having one or more video channels (either the individual video feeds formatted into the transmission format of choice for that broadcast system, or an edited together combination of the feeds) to a transmitter 130. The TV signal is then received at respective user end devices, such as Set Top Box (STB) 140 feeding into an analogue TV 145, or integrated digital TV 150.

In Fig.2, which shows a typical prior art IPTV/broadband video system, the source video feeds 1 10 are inputted into a central video server 220, which digitises the video, if required, and serves up the video content over high speed network links 225 to edge of network video servers 230 having re-processing and aggregation facilities. The edge of network servers 230 then recode the video streams, as required, and serve up video streams to end user devices, such as personal computers 250, normal TVs 145 connected to a PC 250, IP-STBs 240 connected to normal TVs 145, dedicated IPTV devices 245 or other multifunction devices such a computer games consoles, TV fridges, and the like. The re-coded end user video streams are sent over 'last mile' links 235, such as an ADSL link.

Such IPTV/Broadband video systems typically use edge of network server nodes to serve up the required video to end users, because otherwise the data load on the backbone network may be too high, causing failure. Furthermore, such systems typically do not have dedicated bandwidth, because it is shared with other data services to the home (e.g. email, web surfing, online gaming, and the like), therefore is it advantageous to move the server nearer the viewer in order to allow optimal use of the local network capacity.

Moreover, although broadband IPTV/video networks can emulate traditional broadcast networks by using Multicast packets (i.e. a one to many data transmission topology) to send the data to the users, modern VOD (which includes such non-linear services as fast forward, pause, rewind, and the like) means each user must have their own datastream provided using Unicast packets (which is a one-to-one transmission topology). Hence network data rates/saturation levels are ever increasing, which is also encouraging the movement of the video serving nodes to the edge of the network. In these sorts of modern IPTV systems, the source video files may be uploaded to the edge of network video serving nodes from a central source in a single master format, with re-processing of the video being carried out at the edge of network video serving nodes 230 for different playback devices.

Fig. 3 shows a schematic diagram of the hardware contained within a prior art edge of network video server 230. The edge of network server 230 is sourced video content using encoded digital video streams 310 that have been sent over the high speed network links 225 from the central server 220. These source videos are either stored in storage means such as hard drives (not shown), for re-processing at a later time, or are immediately re-processed for onward transmission to the user.

When being re-processed, the source video streams are inputted into one or more (i.e. N instances, where N is the number of subscribers to the IPTV on that node) reprocessing instances 320. Multiple re-processing instances are used because, for example, there is provided a single re-processing instance allocated to a particular user, or a single re-processing instance is provided per output feed type required.

Each re-processing instance typically comprises its own set of picture buffers 323, which are used to store current and past pictures (frames or fields) required by a video metric estimator circuit 324, in order to determine the compression metrics used on the current source digital video. The estimated compression metrics are then used to optimise a subsequent video re-processing step, carried out by video re- processor 325 on the respective previously encoded video stream(s) 310 stored in the temporary video buffer 326, in order to provide an optimised output video stream 390 for the user device (not shown). The video buffer 326 and picture buffer 323 may comprise a single larger buffer.

To enable large scale rollouts of this new type of IPTV or cable broadcast system, the hardware costs must be brought down to comparable levels to the traditional broadcast equipment costs. In this context, the main constraint on the present edge of network processing of video streams is the cost of implementing any meaningful and useful function that adds value to the service, such as the video estimation circuit(s) 324 within the edge network servers 230.

When locally adapting any service element (i.e. video stream) for a specific viewer or group of viewers, the computational and processing resources available/affordable are not great and so this limits the network functionality that can be offered to viewers.

This invention aims to provide solutions to this limitation by proposing to add compression metrics data to a coded video stream at the time of coding, such that downstream network elements may perform high quality re-processing using simpler hardware and software than would otherwise be required had no compression metrics been provided within or alongside the source digital video streams.

The typical embodiment comprises a system having two separate components:

1. A central pre-processing stage, which carries out any one or more of: a. analysing existing compressed video content; b. gathering data about compression characteristics during an encode process; c. gathering data while re-encoding or modifying compressed video content.

The gathered data (i.e. compression metrics) is directly related to the ability of the overall system to efficiently re-process the video content at a second processing stage of the system. The data is then associated with the video content and communicated to one or more re-processing stages.

2. One or more downstream re-processing stages that are adapted to modify the compressed video (e.g. change the bit rate) according to the compression metric data transmitted to the downstream re-processing stages together with the video data.

This downstream re-processing stage, which is typically physically separated from the central pre-processing stage, utilises the compression metrics data gathered in the central pre-processing stage to optimise any bit rate adjustments that are made, either individually, or as part of a co-operative group of video components, such that perceived quality can be managed as a group within a defined bit rate profile for that group.

Fig. 4 shows an overview schematic of an Internet Protocol Digital Television multicast and/or unicast system according to an embodiment of the present invention, in which the bulk of the topology as shown in Fig.2 remains (network connections 225, 235 and end user devices, 240, 245, etc) however, the digital video pre-processing has been moved to a central video processing platform 420 according to the invention. The central processing platform may or may not include storage means, such as hard drives, RAID arrays and the like, depending on whether this is a integrated central video server (inc storage), or an add on component to an existing basic infrastructure.

The central pre-processing platform 420 is connected to one or more downstream slave edge of network re-processors/aggregators 430 by the same network links 225 (the case where the compression metrics are sent over a separate communication links to the video to which they pertain is shown conceptually as separate links 225a and 225b for one instance). The separate communication links may be logically separated, or physically separate.

The slave edge of network re-processors may also be without local storage means (and hence are operable in a real time capacity only), or they may include local storage to allow more non-linear functions (e.g. pause, fast forward, rewind, etc) without recourse to the network links 225, and as such may be termed slave edge of network video servers.

In order to achieve the above mentioned hardware savings at the edge of network devices 430 (re-processors, or servers), the video is pre-processed first at a central point to ascertain or provide compression metrics. In some embodiments, the compression metrics are provided at the point of creation of the digital video, or are estimated using a similar process and hardware as described above with reference to the prior art edge of network servers, as shown in Fig. 3. A single instance of the central processing platform 420 is shown in more detail schematically in Fig. 5.

In Fig. 5 the plurality of video feeds 110 are inputted into a set of picture buffers 525 and video metric estimators 528, which are operable together to determine the compression metrics used in the digital video, as outputted to the edge servers 510. Optional video re-processing 530 can be carried out at this stage also, for example, if the source video is only in analogue form, or if it is at a very high quality (e.g. 108Op High definition) that is too high to reliably send over the network links 225 (or it would be pointless to do so, for example when the system as a whole is only Standard definition).

During this processing stage, the video is compressed, analysed and (re-)formatted for delivery to the edge of network devices 430 for onward provision to users. Compression metrics are gathered which might be relevant to the further processing required at the network edge and these compression metrics are included in the transmission to the downstream re-processing devices (e.g. edge of network video serving devices 430).

Regardless of how the compression metrics are acquired (through estimation, actual calculation, or because the video was compressed in the central processing platform, and hence the actual metrics used are known), the compression metrics are passed, together with the digitised video, to a metric data interleaver/transmitter 540. This portion of the circuit preferably offsets the metrics with respect to the video to which the metrics pertain (such that the compression metrics arrive before the respective portion of video), and then encapsulates the two together in to a single digital data stream.

Fig. 6 shows a typical slave edge of network device according to an embodiment of the invention. The previously encoded digital video streams 510, which include the compression metrics used to digitise the video, are inputted in to one or more instances 620 of the edge of network device, each of which is now only required to contain a data de-interleaver 623 and a much smaller metric buffer 624 compared to the picture buffer 323 required before. Alternatively, in a situation where the picture buffer 323 and video buffer 326 of Fig. 3 would have been combined, when the present invention is applied, the overall video buffer 626 can be considerably smaller then would otherwise have been the case.

Put another way, video buffers become large very quickly, so it is desirable to minimise the size of the video buffers. Normally, when re-processing content, the video needs to be buffered for the purposes of determining its metrics (because the characteristics of that video feed can't be determined and/or used instantly), and also for the purposing of the further re-processing itself. However, by providing the metrics ahead of time, the video feeds don't need to be buffered as much, because the reprocessing node has visibility of the metrics both for the content that has already arrived at the re-processing node, but also, crucially, for the video about to arrive, allowing it to make better decisions based on that advance information. The buffering for the purposing of the re-processing itself is still required though.

The metric buffer 624 controls any required re-processing carried out by a similar re- processor 325 as found in the prior art. Alternative embodiments may share a more complex data de-interleaver, which could service the inputs of all the instances.

Fig. 7 shows an example flowchart of a portion of a method according to an embodiment of the invention 700. The method starts at 710 by centrally processing a video feed (or feeds) to determine compression metrics.

Step 720 comprises interleaving the compression metrics determined at step 710 with the digital video to which the metrics pertain. This may be done with a delay between the metrics and the video to which they pertain, to allow the edge of network devices to receive the metrics in advance of the video.

Step 730 sees the video pushed, or otherwise sent, to the respect slave edge of network devices.

The slave edge of network server will typically be aware of which type of playback it is being asked to carry out - in particular, whether is it to carry out on-the-fly (i.e. realtime) re-processing and playback 750 of the incoming video streams, or whether it is only to store the incoming video streams 760 for later re-processing and playback to the end user device. The device chooses accordingly at step 740.

Examples of the sorts of compression metrics data gathered by the central pre- processing platform 420 and transmitted to the edge devices 430 might include, but are not limited to, the following:

1. bits used per frame for alternative values of quantization parameter (i.e. bit rate); 2. information on bit allocations within and between pictures;

3. video distortion per frame for alternative values of quantization parameter;

4. results obtained by encoding macroblocks in alternate modes (eg. Rate distortion metrics for intra versus inter coding);

5. Drift errors introduced as the result of re-quantization processes;

These compression metrics may either be embedded in the output video bitstream for transmission with the content to the downstream / edge of network processing equipment for a small extra cost in bandwidth, or provided as an out-of-band data path.

The compression metrics may themselves be compressed using an appropriate algorithm, such as Variable Length Coding, or Binary Arithmetic Coding. Importantly, for real-time playback implementations, by delaying the video stream relative to the compression metrics for a short period of time after pre-processing and prior to transmission, it is possible to embed metrics at a point which is offset in time to the portions of video to which they pertain. This effectively allows the compression metrics to be delivered in advance of the content to which they apply, thus allowing time for edge processing elements to implement changes to the coded stream with awareness of future metrics, whilst minimizing cost by reducing unnecessary local storage that would otherwise be required to provide the same functionality (i.e. a smaller video buffer 626 is used, instead of having to provide larger frame buffers 326, and metric estimation hardware 324, in the downstream re-processing device). Examples of where the compression metrics data can be placed within the video data bit stream include, but are not limited to: Transport Packet private data, PES (packetized elementary streams) private data bytes, separate PIDs (packet identifiers), elementary stream user_data and elementary stream supplemental information.

An exemplary simplified embodiment of the encapsulation of compression metrics data into the digital video stream is shown in Fig. 8.

As will be apparent to the skilled person, digital video is typically transmitted in many layers (as in the network OSI model layers), with each layer having its own header, and other data segments which are appended onto the previous layer packet as the data moves up the different layers.

In Fig. 8, the lowest layer is the compression layer 810, where the video is digitised and then packetized 81 1 according the respective compression method in use (for example MPEG-4). In the simplified example shown, these digital video compression packets 811 are passed up to the PES packet layer 820, where in addition to the data payload portion 81 1 , there is provided a space for carrying digital data, which is shown as the metrics portion 822. The metrics data portion 822 has been appended onto the front of the digital video payload 81 1 , after the typical layer header 821.

The resultant PES packet is passed up to the higher layer(s) 830, which takes the previous headed PES packet as the payload 832 for that higher layer 830. The higher layer 830 also appends its own higher layer header 831 on to the payload 832. Finally, a completed digital transport stream 840 is created, ready for sending across network links 225.

Out-of-band path transmission of the compression metrics may utilize synchronization information, such as, for example, presentation time stamp (PTS) values, timecodes, temporal references or GOP (Group Of Pictures) alignment information. These are logical forms of communication link separation. Equally, a physically separate (diverse) transmission path may be used to carry the compression metrics data (e.g. a wireless link), where the compression data is synchronised to the video content, potentially with the aforementioned delay in place also.

The downstream / edge of network video serving devices 430 having the reprocessing stages may then use the look-ahead compression metrics received with, or in advance of the respective video, to process streams in an effective and efficient manner. The presence of the information in advance of the stream to be processed is particularly useful when multiple streams must be processed collectively and cooperatively.

In topologies where the number of downstream/ edge of network video serving devices (i.e. re-processing instances) exceeds the number of pre-processing stages, this invention allows a significant cost reduction of the re-processing hardware whilst achieving the same high performance that could be achieved by having the preprocessing function replicated at every re-processing site.

Also, since the pre-processing hardware is only required at one point, it may be of a much higher quality that would otherwise be cost effective in the edge of network devices. For example, instead of metric estimators, the central processing platform 420 may use metric calculators, which are more complex and costly, but which are more accurate that estimators.

Some traditional broadcast systems do not have the need to replicate the reprocessing hardware, since they use (usually) a fixed standard format of video and audio, and they have dedicated high bandwidth communication channels and compress at the time of transmission. Whereas, others systems, such as IPTV/broadband video networks, cable television networks or mobile telephony systems typically operate over non-dedicated communication channels, and operate in a wide range of different video formats, resolutions, etc, or have a channel line-up that varies by location and time (for example Switched Digital Video in Cable Systems, or shared bandwidth to provide video feeds to mobile handsets). A common use for the present invention is to allow optimal statistical multiplexing of a plurality of variable bit rate data streams (usually video, but may include data, voice, or other data too) into a single constant bit rate data stream for sending over an onward network link, using simplified hardware at the edge of network server device. This is often termed collaborative processing, and it is commonly seen at the edge of network servers for Cable Television systems, which share a fixed bandwidth between multiple customers, or for IPTV systems which also provide internet access, voice, messaging email etc down a single fixed rate last mile connection links, such as an ADSL (or ADSL 2+) link.

Bit rate changing, in particular changing down to a lower bit rate (i.e. where bits are dropped, as opposed to completely decoding and then recoding at a different, lower bit rate) particularly benefits from the present invention, since the provision of compression metrics determined when encoding or pre-processing previously compressed digital video that detail the quantisation parameters used or the characteristics of bit rate and quality as a function of quantisation parameters, etc, allows quick and accurate determination of the sensitivity of the source video content to re-processing, allowing optimal re-processing techniques to be applied, either for single services or collaboratively to ensure quality targets are met across a group of services that share a given bandwidth. Thus, embodiments of the invention provide the information used to re-format the video content that would otherwise have had to be derived at the edge of network devices themselves. This reduces the complexity, and hence cost, of the edge of network devices according to embodiments of the invention.

The present invention may also be used in networked Personal Video Recorders, i.e. hard drive based, non-linear recorders for recording TV (that may also link together to serve up a greater range of content than a single PVR can manage), as a way to assist in determining how much bandwidth a recording will require on playout, and how it may be collaboratively processed with other video services, or re-processed to fit within a limited bandwidth (e.g. for IPTV). Standard definition video is understood to be any video sized up to 720 columns, such as 48Oi (i.e. 720 x 480), as used in the NTSC TV standard or 576i (720 x 576) as used in the PAL TV standard.

High definition video is understood to mean any video at a higher column/line resolution than standard resolution. At the time of inception of the present invention, this includes 72Op (1280x720), 108Oi (1280 x 1080) or 108Op (1920 x 1080), 216Op (3840 x 2160), etc.

The above described method maybe carried out by suitably adapted or designed hardware. Portions of the method may also be embodied in a set of instructions, stored on a computer readable medium, which when loaded into a computer, Digital Signal Processor (DSP) or similar, causes the computer to carry out the hereinbefore described method.

Equally, the method may be embodied as a specially programmed, or hardware designed, integrated circuit which operates to carry out the method on video image data loaded into the said integrated circuit. The integrated circuit may be formed as part of a general purpose computing device, such as a PC, and the like, or it may be formed as part of a more specialised device, such as a games console, mobile phone, portable computer device or hardware video encoder. This is a preferred implementation for HDTV applications.

Although the above described embodiments of the invention have been described in terms of an IPTV broadcast system, it will be apparent that the core inventive concept of providing digital video compression metrics within the compressed digital video stream itself, or as a separate logical/physical transmission alongside the main digital video stream, may be equally applied to any system that captures/stores video that may be subsequently re-processed. Such systems include Cable Television Systems, Mobile Telephony Video systems, Local Wireless networks, CCTV systems, video editing systems, TV cameras, camcorders, Personal Video Recorders, webcams and the like. One exemplary hardware embodiment is that of a Field Programmable Gate Array (FPGA) programmed to carry out the described method and /or provide the described apparatus, the FPGA being located on a daughterboard of a rack mounted video server held in a data centre, for use in, for example, a IPTV television system and/or, Television studio, or location video uplink van supporting an in-the-field news team. The provision of compression metrics together with the master source feed allows quicker and better downstream re-processing of the video data. Furthermore, it also assists in the provision of concurrent finished (edited) and raw video feeds, as is now often desired in the massively multi channel television systems, where keen viewers wish to see the un-adulterated video, whereas others wish to see a (potentially lower quality) preview of the video, full resolution finished edited version, or the like.

Another exemplary hardware embodiment of the present invention is that of a central video server including a pre-processor and compression metric interleaver constructed using an Application Specific Integrated Circuit (ASIC).

Another exemplary hardware embodiment of the present invention is that of a cable television edge processing device, where a number of previously compressed video streams must be formed into one or more digital cable transport streams, the line-up of which may vary over time depending on viewer selections within the cable television edge processing device. The method and apparatus described herein may be used to optimise use of the available bandwidth to cost-effectively increase the number of video services carried by each cable transport stream by allowing collaborate bit-rate distribution through the re-processing of the video services to meet the bandwidth available.

A further exemplary hardware embodiment of the present invention is that of a mobile telephony base station, where the number of video services required varies, amongst other criteria, on the location of mobile handsets. In this embodiment, a software program running on the base station platform, or a hardware implementation, takes video services at original bit rates and reprocesses these to fit within a mobile telephone carrier system (e.g. DVB-H, or a 3G video data bearer), potentially also sharing that capacity with data or voice services.

Claims

Claims:

1. A method of transmitting digital video comprising: determining compression metrics about the digital video; and transmitting the compression metrics together with the digital video to which the metrics pertain.

2. The method of claim 1 , wherein the step of determining the compression metrics further comprises any one or more of: carrying out pre-processing analysis of a previously digitised video to determine the compression metrics used previously; or gathering compression metrics used to digitise the digital video at a time of digitising; or gathering compression metrics about the digital video while re-encoding or modifying the digital video content or by pre-analysis of uncompressed video content.

3. The method of any preceding claim, wherein the compression metrics are transmitted offset in time from the point in the digital video to which they pertain.

4. The method of any preceding claim, wherein the compression metrics and digital video to which they pertain are incorporated into a single digital video stream.

5. The method of any preceding claim, further comprising: receiving the digital video at a remote location; and re-processing the digital video in accordance with an onward transmission requirement.

6. The method of any preceding claim, wherein the digital video is to be carried over an Internet Protocol, Cable Television or Mobile Telephony based digital video transmission system, and the method further comprises: providing a central pre-processing device for carrying out the steps of determining the compression metrics, and transmitting said compression metrics together with the digital video to which they pertain; providing at least one edge of network video serving device for carrying out the steps of receiving the digital video at a remote location and re-processing the digital video in accordance with an onward transmission requirement, said at least one edge of network device including a compression metric buffer to receive said compression metrics, and a re-processor to re-reprocess the digital video.

7. The method of claim 6, wherein the system processes a plurality of digital input streams concurrently to provide a plurality of compression metrics about said digital input streams, and the method further comprises: re-processing each digital video input stream according to the compression metrics of the plurality of digital input streams at the at least one edge of network digital video processing device.

8. The method of claim 6 or 7, wherein the re-processing includes carrying out any one or more of: recoding the digital video; or changing the bit rate of the digital input streams.

9. The method of claim 7 or 8, wherein the plurality of digital input streams are variable bit rate, and the re-processing comprises changing the bitrate of the digital input streams, and the method further comprises: combining the re-processed digital input streams to form a defined aggregate bit rate output stream profile.

10. An upstream centralised video pre-processor for use with a digital video transmission system, comprising: at least one video feed input; a video pre-processor in communication with the at least one video feed input and adapted to provide video compression metrics information about the video feed; and a compression metric and video feed transmitter, adapted to transmit the video compression metrics and video feed to at least one downstream video re- processor.

1 1. The centralised video pre-processor of claim 10, wherein the video preprocessor is further adapted to provide the compression metrics by means of any one or more of: carrying out pre-processing analysis of the video feed to determine the compression metrics of previously compressed content; or gathering compression metrics used to digitise the video feed at a time of compressing; or gathering compression metrics about the video feed while re-encoding or modifying the video feed content.

12. The centralised video pre-processor of claim 10 or 1 1 , wherein the compression metric and video feed transmitter is adapted to transmit the compression metrics offset in time from the point in the video feed to which they pertain.

13. The centralised video pre-processor of any of claims 10 to 12, wherein the compression metric and video feed transmitter is further adapted to incorporate the compression metrics and the video feed to which they pertain into a single output digital video feed.

14. The centralised video pre-processor of any of claims 10 to 12, wherein the compression metric and video feed transmitter is further adapted to transmit the compression metrics over a separate communication link from the video feed.

15. The centralised video pre-processor of any of claims 10 to 14, wherein the central pre-processor comprises a plurality of individual pre-processors operable as a single shared resource.

16. A downstream video re-processor, comprising: a compression metric receiver; a compression metric storage buffer; and a video re-processor, adapted to re-process incoming digital video data according to compression metrics accompanying the digital video data previously received and stored in the compression metric buffer.

17. The video re-processor of claim 16, wherein the re-processor is adapted to reprocess incoming digital video data by carrying out any one or more of: recoding the digital video; or changing the bit rate of the digital video.

18. The video re-processor of claims 16 or 17, wherein the incoming digital video comprises a plurality of variable bite rate input digital video streams, and the re- processor is further adapted to re-processing said input digital video streams to form a single constant bit rate output digital video stream.

19. A system comprising: at least one video input feed; an upstream centralised video pre-processor in communication with the at least one input video feed and adapted to provide video compression metric information about the input video feed; a compression metric and digital video transmitter, adapted to transmit the video compression metrics and the digital video to which the metrics pertain to at least one downstream video re-processor; and at least one remote video re-processor in communication with the compression metric and digital video transmitter.

20. A method of receiving digital video comprising: receiving compression metrics together with the digital video to which the compression metrics pertain; and using the compression metrics in further re-processing of the digital video.