WO2012076904A1

WO2012076904A1 - Video data transmission system and method

Info

Publication number: WO2012076904A1
Application number: PCT/GB2011/052451
Authority: WO
Inventors: James Chung -How; David Bull; Andrew Nix; Jon Pledge; Dimitris Agrafiotis; Robert Stapenhurst
Original assignee: Gi Provision Ltd
Priority date: 2010-12-10
Filing date: 2011-12-09
Publication date: 2012-06-14
Also published as: GB201020949D0; GB201314210D0; GB2501843A; GB201102616D0

Abstract

The invention provides a method of controlling a video transmission system, the method comprising receiving an input indicative of a desired mode of operation, automatically configuring transmission parameters in dependence upon the desired mode of operation indicated by the received input and encoding and transmitting a video datastream over a communications channel using such transmission parameters. Also provided is a video transmission system comprising a video source operable to generate and output a video datastream, a user input device operable to receive a user input indicative of a desired mode of operation, a datastream encoder and transmitter unit operable to receive user input information from the user input device, to configure transmission parameters in dependence upon a desired mode of operation indicated by a received user input, and to encode and transmit a video datastream over a communications channel using transmission parameters.

Description

VIDEO DATA TRANSMISSION SYSTEM AND METHOD

In wireless High Definition (HD) video and content delivery, providing low latency so that interactive applications can be supported as well as maintaining high quality in the presence of compression and loss so that the quality expectations of the user are satisfied are complex requirements. For example, when multiple video channels exist, the joint adaptation of the independent wireless and video data rates is complex and, in some cases, it may not be possible to satisfy desired delay and quality constraints. For example, in gaming, delayed content delivery can compromise the user experience whereas in the case of video, poor quality compression and loss would be undesirable.

A system which is based on a wireless standard such as 802.11η and a video codec such as H.264 can be used to compress and stream video to a client. Such a system can allow compression to take place in real time, for example using an encoder or transcoder in a set top box that receives a signal off air and then which transcodes it to a format and rate suitable for redistribution. Such systems must cope with time-varying data bandwidth of the communications channel and often incorporate large amounts of buffering to deal with this. In live steaming systems for example, delay is often a key parameter as it affects session start up times and, in interactive applications, may be visible to the user throughout the session. Poor responsiveness as a result of delay can be detrimental to the user experience. Designers therefore often seek techniques for maintaining a balance between high video quality, low probability of playout disruption and low end to end delay.

Existing techniques for attempting to maintain quality and minimise delays of streamed data typically use video source rate adaptation, relying on tight coupling between the encoder's rate control and the overall system controller. Furthermore, certain rate adaptation schemes can require metrics and controls which are not available to the designers of practical streaming systems (i.e. the functionality is not available in the video encoder). In one such system, delay constraints are considered in sub-frame sized blocks and, using predictions of the future channel rate from a model, rate constraints can be derived. From these derived rate constraints, appropriate quantisers can be chosen to minimise expected distortion in video quality. In another rate adaptation system, individual frames are transrated based on their delivery deadlines. A distortion model is used to optimise the scaling factors over a group of frames. The two main parameters used in this system are chosen adaptively using the result of a packet train dispersion analysis, fed back from the client. The system relies on having precise control over individual frame sizes.

An aim of the present invention is to provide a system and method whereby adaptation of the video is possible to allow the same to be suited to specific modes of use of the apparatus and which modes can be selected by the user and/ or in response to another control means.

According to a first aspect of the present invention, there is provided a method for controlling a video transmission system, the method comprising: receiving an input indicative of a mode of operation;

automatically configuring transmission parameters in dependence upon the desired mode of operation indicated by the input; and

encoding and transmitting a video datastream over a communications channel using such transmission parameters.

In one embodiment the input is generated by user interaction with the apparatus to select a particular mode. In an alternative embodiment the system determines the mode to be used based on detected conditions and then generates the input to reflect the selected mode such that the selection and input is automatically generated.

Typically the transmission parameters include video encoder parameters.

In one embodiment the said input is generated by user interaction with the system. In one embodiment the video transmission system is operated via a wireless communication medium.

Typically, the method of controlling the wireless video transmission system ensures that the video transmission is suitable for the purpose of use which is reflected in the desired mode of operation and enables the transmission parameters to be set at the most appropriate values for the mode of operation.

In one embodiment, the method further comprises estimating channel conditions for the wireless communications channel, and using such predicted channel conditions in the configuration of the transmission parameters.

Typically, the use of the intended mode of operation in conjunction with the estimated channel conditions allows the configuration of the transmission parameters to be optimised for the desired mode of operation.

In one embodiment, the estimating of channel conditions can be repeated during the datastream transmission. A transmission can therefore be optimised on an ongoing basis to refine transmission parameters taking into account the predicted ongoing channel conditions.

In one embodiment there is provided a wireless video transmission system providing switchable modes of operation and typically the modes of operation can be controlled by the user according to a use-case or content type.

In one embodiment the modes of operation can include, for example, any or any combination of: an interactive low-delay mode, a 'normal' mode, such as for general use, and a movie mode in which quality can be prioritised. In one embodiment the interactive mode provides a low latency link for channel hopping and interactive services such as set top box (STB) menus and games and so on, the movie mode provides increased buffer delay to facilitate reduction of peak data rate over the wireless channel and/or increased retransmission of data and/ or repair of packets.

In one embodiment a means for a user to control an operating mode can be, for example, a single remote control button to flip between modes.

In one embodiment the selection of an operating mode causes buffers to be suitably configured and video coding parameters to be selected to support the mode in question..

In one embodiment the parameters can be selected to support the mode in question such that, for example, a windowed rate adaptation scheme for transmitting delay-constrained video over a wireless channel can be used which uses an H.264 encoder with Hypothetical Reference Decoder (HRD)- compliant rate control and generic 802.11-like radio. Such a scheme assumes only loose coupling between systems components which improves implementation feasibility.

In one embodiment the method may further comprise configuring a buffer of the wireless video transmission system in dependence upon the desired mode of operation indicated by the received user input.

In a further embodiment, the method further comprises selecting video coding parameters in dependence upon the desired mode of operation indicated by the received user input.

By selecting the video coding parameters in this way, characteristics of the datastream can be controlled to ensure they are appropriate for the desired mode of operation and the channel conditions. The desired mode of operation can be chosen from a high quality mode in which buffer size is increased, and a low latency mode in which buffer size is decreased. Datastream transmission can therefore be optimised so that a probability of playback disruption is decreased.

Configuration of the transmission parameters includes video source rate adaptation. Datastream transmission can therefore be tailored accordingly so that the probability of playback disruption is minimised.

A further aspect of the present invention provides a video transmission system comprising:

a video source to generate and output a video datastream;

a datastream encoder and transmitter unit to receive input to configure transmission parameters in dependence upon a desired mode of operation indicated by a received input, and to encode and transmit a video datastream over a communications channel using such transmission parameters.

In one embodiment the system includes a user input device operable to receive a user input indicative of a desired mode of operation and the datastream encoder and transmitter unit is operable to receive user input information from the user input device.

In one embodiment the video transmission is achieved over a wireless communication channel.

In one embodiment the system may further comprise a channel estimator operable to estimate channel conditions for a wireless communications channel, the datastream encoder and transmitter operable to use the estimated channel conditions in the configuration of transmission parameters. Accordingly, transmission parameters can be optimised for the desired mode of operation by taking account of the predicted channel conditions for the time of transmission. Such a channel estimator can be used to determine channel conditions repeatedly during datastream transmission. This repeated determination allows a transmission configuration to be optimised on an ongoing basis so that the most appropriate transmission parameters can be selected.

In one embodiment, the encoder and transmitter unit include a video data buffer, and it is operable to configure the video data buffer in dependence upon the desired mode of operation indicated by the received user input. Accordingly, the datastream transmission can be optimised so that the probability of playback disruption is decreased. The encoder and transmitter unit is operable to select video coding parameters in dependence upon a desired mode of operation indicated by a received user input so that characteristics of the datastream can be controlled to ensure they are appropriated for the desired mode of operation and channel conditions.

The desired mode of operation may be chosen from a high quality mode in which buffer size is increased, and a low latency mode in which buffer size is decreased.

Typically, the option to choose a high quality mode or low latency mode means that datastream transmission can be optimised for the use, and that the probability of playback disruption is decreased.

In a further embodiment of the system, the encoder and transmitter unit is operable to configure the transmission parameters using source rate adaption, therefore further ensuring that datastream transmission can be optimised and the probability of playback disruption is decreased.

According to one example, there is provided a datastream transmission device to receive input data representing a mode of operation for the device, receive a video datastream to be transmitted, select a set of parameters for transmission of the video datastream on the basis of the mode of operation, modify the video datastream on the basis of the selected parameters, and transmit the modified video datastream over a communications channel. Modification of the video datastream can include to encode, transcode, adapt or otherwise process the video datastream. To adapt the video datastream can include selecting multiple portions of the video datastream to provide a substream to represent the video datastream with a reduced bit rate. Such a device can further include a channel estimator to estimate channel conditions of the communications channel, such that the encoder can use the estimated channel conditions in the selection of the parameters for transmission.

The method and system of the present invention are typically described herein with reference to wireless transmission of data. However, a communications channel according to the features described above and the examples described below need not be limited to being a wireless channel. For the sake of clarity and brevity, reference to a wireless channel is predominantly used, but this is not intended to be limiting, and non-wireless or hybrid systems and environments including wireless and non-wireless (such as wired) components are suitable for use. Reference to 'wireless' should be construed accordingly. For example, the invention, and the system and method described herein, may be implemented via wired communication systems based on fibre optic or coaxial cable connections.

Specific embodiments of the invention will now be described, by way of example only, and with reference to the accompanying drawings, in which:

Figure 1 is a schematic block diagram illustrating a wireless video transmission system according to one embodiment of the invention;

Figures 2 and 3 are graphs showing performance parameters of a wireless video transmission system according to an embodiment of the invention;

Figure 3a is a schematic block diagram of a video transmission system according to an embodiment of the invention; Figure 4 is a schematic block diagram of a method of controlling a video transmission system according to an embodiment of the invention;

Figure 5 is a schematic block diagram of a video transmission system according to an embodiment of the invention; and

Figure 6 is a schematic block diagram of a video transmission system according to an embodiment of the invention.

Figure 1 illustrates a wireless video transmission system 1 according to an example which includes a video source 10 which in this case is a video encoder or transcoder. The source 10 generates a video datastream. According to an example, unencoded video data input to the video source 10 can be encoded into a coded video bitstream to form a generated video datastream. Alternatively, previously encoded video data input to the video source 10 can be transcoded into a coded video bitstream to form a generated video datastream. Further alternatively, scalably encoded video input to the video source 10 can be adapted, modified or processed in order to produce an alternate suitable coded video bitstream forming a generated video datastream. For example, parts of a scalably encoded video datastream can be removed or discarded to provide one or more substreams representing the source content but with a bit rate which is less than that of the complete original video input.. Such substreams can be suited to current channel and buffer conditions as will be described below.

According to an example, the datastream is compliant with suitable video buffer verification model rate control parameters, such as HRD parameters for example (as described in standards such as H.264/AVC). That is to say, there are constraints on the variability of a conforming datastream produced by the video source 10 according to an example. An encoded, transcoded or otherwise processed video datastream is supplied to a transmit buffer 12, and then to a radio transmitter 14. The transmitter 14 operates in a known manner, and so its detailed operation will not be described here. The radio transmitter 14 operates to transmit a wireless radio frequency variable bit rate (VBR) signal 16 containing a packetized form of the video datastream to a radio receiver 20. The radio receiver 20 decodes the received radio frequency signal into a received datastream which is supplied to a receiver (rx) buffer 22. The receiver buffer 22 then supplies the received datastream to a video sink for example, a player.

The system 1 provides a number of modes of operation. Typically there will be three modes of operation which can be selected by the user. According to one example, the three modes of operation are a low delay interactive mode, a normal mode for general use and in which quality and delay are given approximately equal priority and a movie mode in which quality is prioritised. Source rate adaptation is provided in any of these modes to enable the system to deliver the desired video quality at a pre-determined delay over a long period of time.

Within the system 1, a frame work is provided for rate-adaptive streaming whereby the source rate adaptive scheme requires only loosely coupled system components, yet can still benefit from any additional information or control available. For system component coupling in this case, the video encoder's rate control is compliant with that of a suitable video buffer verification model, such as the H.264/AVC HRD for example.

Following packetisation by source 10, data packets are delivered to the transmission buffer 12, in preparation for transmission from transmitter 14. Mismatched source and channel rates are reconciled using buffer 12 as will be described below in more detail. Data packets are transmitted by transmitter 14 over VBR channel 16 and received by receiver 20. The process is then reversed with the datastream received by receiver 20 and provided to reception buffer 22 before being provided to the client, in this case video sink 24. The data can then be displayed to a user in the required format. Assuming negligible encode, decode and channel propagation times, the end to end delay of the system 1 is defined by the total amount of buffering delay in transmitter buffer 12 in combination with reception buffer 22.

In order to enable the user to select an appropriate operating mode, the modes which are available utilise a source rate adaptation scheme which controls the characteristics of the encoded bitstream, within certain delay constraints, by specifying video buffer verification model parameters to the video encoder. According to an example, each operating mode maps to an appropriate set of such parameters.

According to an example, the rate adaption scheme operates on a windowed basis by predicting channel behaviour then choosing appropriate video buffer verification model parameters for an upcoming transmission window. The channel prediction step can use a model of channel behaviour which is updated at the beginning of each window using data collected during the previous period. The nature of these data updates is implementation specific and depends on the channel monitoring capabilities present in system 1. The data collected may include, but is not limited to, statistics such as received signal strength indication (RSSI) and/ or retry rates and/ or automatically selected modulation scheme of a wireless channel. The channel monitoring capabilities can include the presence of a bandwidth monitoring scheme. It will be appreciated that other statistics or system data may be collected and collated for use in the creation of a channel behaviour prediction.

Based on the channel behaviour prediction generated by the model and on buffer occupancies within system 1, the parameters for the rate control are adjusted. The rate control adjustment aims to ensure that the decoder buffer does not underflow during the upcoming period. In an ideal system, the channel behaviour prediction is accurate and the rate control complies with the HRD specified parameters. Thus underflow and hence playout disruption is avoided. In real life implementations, errors in the data bandwidth prediction of channel 16 can occasionally occur and may result in occasional underflow of data in buffer 22. As the potential for occasional underflow is known, then if the error bounds on the predicted bandwidth are known, or can be estimated, worst case channel behaviour prediction can be used to adjust the rate control. The use of a worst case adjustment reduces the probability of playout disruption but increases the compression of the video, therefore reducing quality. In the event of underflow, the parameters are set such that bitstream size is reduced and playout resumes as soon as possible.

To describe the state of the system, a playout curve, p{f) an example of which is shown in Figure 2, can be provided. The curve expresses the total number of bits produced by the encoder at any given time /. The curve p{f) is monotonically non-decreasing and is bounded by p(f)< pit) < p J) for all /. These bounds are imposed by virtue of the source's HRD compliance. Similarly, the quantity of data received at the client is represented by r(i), the receiver curve. According to an example, negligible packet loss is assumed. Typically, this can be achievable by means of a link layer retransmission scheme or similar. Changes in network throughput manifest themselves as variation in the gradient of r(i). Regardless of the channel condition, r(i) is bounded by pit) as the coded bitstream is generated in real time so it is not possible to transmit more data than has been generated at a given time.

The end to end delay of the system, Δ, is taken as a design parameter, selected by the user or set automatically by the system, and is the time between the insertion of a frame into the transmitter buffer 12 and the removal of that frame from the receiving buffer 22. Such delay is considered to be fixed for the duration of the session. According to an example, a constraint curve is defined as cit)— rit + Δ) and is a time-shifted version of the receiver curve r(i). This constraint curve represents the upper bound on the playout curve at the receiver. The aim of the adaptation scheme is therefore to manipulate the encoder such that pit) < c(t) for the duration of the streaming session.

According to one embodiment, a given mode of operation maps to appropriate transmission rate and buffer size parameters for the system. That is to say, for the datastream in question, and for which a user has selected an appropriate mode of operation of the system, each mode represents the selection of an appropriate set of parameters. Each set characterises a model including three values— a peak transmission rate buffer capacity b_v and encoder-side startup delay (in seconds) d_e.

The HRD, or similar verification model, buffer duration is δ_ν = b^R^. The upper bound on p{f) can therefore be derived as p i)— p(f)+b_v , where the lower bound is given by p{f) — R^ t - d^). The lower bound is not a bound as such; it represents the point at which the encoder buffer empties. If p{f) falls below p{f) then both p{f) and pu{f) must be recalculated. In any practical wireless streaming system, the nature of the channel makes it difficult to know the available bandwidth in advance. To make rate decisions, the system 1 must form an estimate of future channel behaviour. These estimates of future channel behaviour are represented by curve, r(t ). In this example, r(f)<r() is satisfied for a given realisation of r(i) with probability n. The constraint curve c{f) , being a time-shifted version of r(i), has a similarly defined lower bound c(f). It is assumed that r(i) and c{f) are monotonically increasing.

In use, the user can select an operation mode to be used. The selection of the operation mode can be performed, for example, prior to the start of a movie or gaming ses sion, although it may also be selected during transmission, in which case there may be some disruption to video quality while buffering and associated parameters are reconfigured and the system adjusts. According to an example, the system 1 uses a windowed HRD parameter adaptation scheme which runs with a period known as the window duration. A short window can be used as it will enable the system to be more responsive to changes in the environment such as a change in operation mode for example. It will be appreciated that shorter windows are desirable to facilitate responsiveness. The encoder's rate control in this case defines the minimum permitted window, w, in a given implementation; for example, the encoder may permit parameter adjustment only at pre-defined instantaneous Decoder Refresh (IDR) frames. In this case a suitable window duration and phase is chosen to match the IDR interval. According to one embodiment, at the start of each window, the controller performs the following steps:

1. Update channel model with any new information;

2. Form predictions for channel behaviour over upcoming window; and

3. Choose HRD parameters for the upcoming period according to the predictions.

Figure 3 shows an example of the information available to the controller at some time, f , during a streaming session. The historic source rate is known. The achieved rate r(i) is determined to some desired degree of resolution by periodically measuring the changes in buffer occupancy. The achieved r(i) may alternatively be determined using other metrics, such as provided by a radio in a particular implementation. It will be appreciated that r(i) is not necessarily identical to the channel bandwidth as its value is restricted by r( )≤>( ). If the channel rate is higher than video rate for a sufficient period of time, this bound will be met. The value of c (/) is known only for / <f -A. Predictions for the upcoming period are shown by r(i) and c(j) in figure 3.

There are various methods which could be used to find r_r{f) and c_r{f) for a corresponding probability n. The method chosen will depend on information available to the controller. For example, an implementation can use retransmission statistics (if made available by a radio) in estimating r(i) and c(i). According to an example, a suitable controller obtains information from various parts of the system 1 and performs adaptation by modifying parameters elsewhere in the system.

Figure 3a is a schematic block diagram of a video transmission system 100 according to an example. Controller 200 can receive information from the receiver 20 and/ or buffer 22, via an in- or out-of-band back channel. Controller 200 can receive information from video source 10, tx buffer 12 and/ or tx radio 14. The controller is operable to use information gathered from parts of system 100 to modify parameters for the system 100. The lower part of the network stack referred to above can include a physical (PHY) layer and a data link layer as de fined in the open systems interconnection (OSI) model for example. The PHY layer is typically part of radio hardware (not shown), whereas the data link layer can exist in the radio hardware in software executing on a processor to which the radio hardware is attached or otherwise communicating.

As detailed above, the type and quality of available metrics, for example the retry rate, the packet loss rate and RSSI, etc. can influence both the choice and performance of a channel behaviour prediction scheme. In some embodiments of the system, if client feedback is available within an appropriate time frame, reporting mechanisms can provide information from receiving radios or enable probing techniques to increase the quality of prediction.

With r(\ and c(t) specified, the set of parameters is chosen. The value of is given by.

This sets a constraint such that p_u{ - + w)— c(t* + w) i.e. at the end of the upcoming window, p{f) will lie below c{f) with probability n (assuming that the encoder's rate control does not violate verification model constraints). In some cases can be clipped so that it lies within an acceptable range. The upp er b o und o f s uch acc ep table range c an b e d e fin ed by the encoder/ decoder level and the lower bound by the lowest feasible bitrate for the encoder for example. The buffer size b_v is then found by: -p_a{ ) + -τψ + w)

As with B^, b_v can be clipped to meet any constraints imposed by the encoder or the encoder level. The video buffer verification model parameters for the first window cannot be chosen in the same way as described above as no knowledge of the channel behaviour is available for use in generating the prediction prior to the first window. Instead, for the first window, a channel prediction can be obtained during session initialisation. Such a channel prediction can be obtained in various different ways. For example, rate estimations can be obtained from statistics of recently-transmitted packets or dummy packets, or a channel prediction can be formed using RSSI figures from a radio.

During implementation, inaccuracies in the channel prediction can occasionally result in decoder underflow. If such underflow occurs, the decoder is typically able to decode the frames when they eventually arrive and catch up with the original playout schedule, suffering only jitter in the frame display times. Nevertheless, this jitter may be visible to the user and thus should be avoided if at all possible. If it is found that p{f^f)>c{f^)f) during the adaption process, one or more frames will be delayed with a probability of at least n according to an example. To minimise the number of delayed frames, an alternative formula for can be used:

where t_t the recovery time, is the desired time until p i) is first less than or equal to c(t).

Figure 4 is a block diagram of a method according to an example. In block 401 a system, such as system 1 in figure 1 for example, receives a user input indicative of a desired mode of operation. According to an example, the user input can be provided using a dedicated remote control device or certain functions on an existing remote control device (such as using appropriately configured button(s) on a pre-existing remote control). In block 403, the system configures transmission parameters in dependence upon the desired mode of operation as indicated by the received user input. In block 405, encoding, transcoding, processing or otherwise adapting a video datastream for transmission over a communications channel occurs using the configured transmission parameters.

Figure 5 is a schematic block diagram of a video transmission system 500 according to an example. A video source 501 produces a video datastream 503 for consumption by a user of the system 500. The video datastream can be a movie, programme, portion of video, such as a portion used in a videogame, or any other sequence of still images representing scenes in motion for example. A user input device 505, such as a remote control device for example, is used to provide user input data 507 indicative of a desired mode of operation 509 of system 500. The user input device 505 can be part of the system 500, or can be a device which is part of a consumption apparatus, such as a television, monitor, or other display apparatus for example.

According to an example, the mode of operation 509 is a tailored mode for transmission of the datastream 503, and which is designed, in one example, to maximise quality or minimise latency of transmission. Video datastream 503 and the mode of operation 509 are input to block 511 which includes a datastream encoder 513 and datastream transmitter 515. According to an example, encoder 513 and transmitter 515 can be distinct modules of the system. However, it will be appreciated that they can be incorporated into the same module without any loss of functionality. Encoder 513 is used to encode video stream data 503 into a format suitable for transmission and/or consumption. Encoder 513 can also function as a transcoder or module suitable for adapting a video datastream, such as adapting into a suitable video substream for example. Transmitter 515 can be a suitable wireless radio frequency transmitter. According to one embodiment, transmission parameters 517 are parameters which are suitable for the mode of operation 509. The suitably encoded datastream is transmitted over a communications channel, which can be a wireless communications channel.

Figure 6 is a schematic block diagram of a video transmission system 600 according to one embodiment. Similarly to system 500 of figure 5, the system 600 includes a video source 501 which produces a video datastream 503 for consumption by a user of the system 600. A user input device 505, such as a remote control device for example, is used to provide user input data 507 indicative of a desired mode of operation 509 of system 600.

According to the embodiment shown, the mode of operation 509 is a tailored mode for transmission of the datastream 503, and which is designed to maximise quality or minimise latency of transmission for example. Video datastream 503 and the mode of operation 509 are input to block 511 which includes a datastream encoder 513 and datastream transmitter 515. According to an example, encoder 513 and transmitter 515 can be distinct modules of the system. However, it will be appreciated that they can be incorporated into the same module without any loss of functionality. Encoder 513 is used to encode video stream data 503 into a format suitable for transmission and/or consumption. Encoder 513 can also function as a transcoder or module suitable for adapting a video datastream, such as adapting into a suitable video substream for example. Transmitter 515 can be a suitable wireless radio frequency transmitter. According to the embodiment, transmission parameters 517 are suitable for the mode of operation 509. The suitably encoded datastream is transmitted over a communications channel 601.

A channel estimator 603 estimates channel conditions for such a communications channel 601. The datastream encoder 513 and transmitter 515 are operable to use such predicted channel conditions in the configuration of transmission parameters 517. The channel estimator 603 can estimate channel conditions repeatedly during datastream transmission.

Communications channel 601 can be a wireless communications channel.

Various modifications may be made to the embodiments as hereinbefore described without departing from the scope of the invention. For example the system 1 has been described as having three modes of operation, however it will be appreciated that the system 1 may be provided with more or less than three modes depending on the types of use of the system. In addition, video source 10 has been described as being an encoder or transcoder but may be any source suitable for generating data bitstreams, such as a source for adapting a scalable bitstream to provide substreams (such as in the case of bitstreams conforming to annex G of the H.264/AVC standard for example).

Furthermore, whilst it has been detailed that the user will first select the operation mode to be used and generate the input, it will be appreciated that in an alternative embodiment, the system may be operable to self select the mode of operation and create the input to reflect this such that and this self selection may be carried out intelligently in response to indicators provided by the datastream. For example, during encoding, transcoding or adaptation, the system can use some form of video content analysis to determine the content of a portion of video and select a mode of operation of the system accordingly and generate an input to reflect this. Typically, such video content analysis can include motion detection to determine the presence of relevant motion in multiple scenes in the video object detection to determine the presence of a type of object or entity; and face recognition to detect the presence and movement of one or more people. Other alternatives are possible.

Claims

CLAIMS:

1. A method for controlling a video transmission system, the method comprising:

receiving an input indicative of a mode of operation;

2. A method according to claim 1 wherein the said input is generated in response to user interaction with the system to indicate the desired mode of operation.

3. A method as claimed in claim 1, further comprising estimating channel conditions for the communications channel to provide estimated channel conditions, and using the estimated channel conditions in the configuration of the transmission parameters.

4. A method as claimed in claim 3, wherein estimating channel conditions is repeated during the datastream transmission.

5. A method as claimed in any of claims 1-4 further comprising configuring a system buffer of the video transmission system in dependence upon the desired mode of operation indicated by the received input.

6. A method as claimed in any one of the preceding claims, further comprising selecting video coding parameters based on the desired mode of operation indicated by the received user input.

7. A method as claimed in any one of the preceding claims, wherein the desired mode of operation is chosen from a high quality mode in which a system buffer size is increased, and a low latency mode in which a system buffer size is decreased.

8. A method as claimed in any one of the preceding claims, wherein configuration of the transmission parameters includes source rate adaptation.

9. A method as claimed in any one of the preceding claims, wherein encoding a video datastream includes encoding, transcoding or otherwise processing the video datastream for transmission.

10. A method as claimed in claim 9, wherein otherwise processing the video datastream includes adapting or modifying the video datastream to provide a video substream representing the source content of the video datastream with a bit rate which is less than that of the video datastream.

11. A method as claimed in any one of the preceding claims, wherein the communications channel is a wireless communications channel.

12. A video transmission system comprising:

a video source to generate and output a video datastream;

13 A system according to claim 12 wherein the system includes a user input device to receive a user input indicative of a desired mode of operation.

14 A system according to claim 12 wherein the input is generated automatically by the system dependent upon detected conditions at that time.

15. A system as claimed in claim 12, further comprising a channel estimator to estimate channel conditions for the communications channel, the datastream encoder and transmitter to use such predicted channel conditions in the configuration of transmission parameters.

16. A system as claimed in claim 15, wherein the channel estimator us used to estimate channel conditions repeatedly during datastream transmission.

17. A system as claimed in any one of claims 12 to 16, wherein the encoder and transmitter unit includes a video data buffer, the encoder and transmitter to configure the video data buffer in dependence upon the desired mode of operation indicated by the received user input.

18. A system as claimed in any one of claims 12 to 16, the encoder and transmitter unit to select video coding parameters in dependence upon a desired mode of operation indicated by a received user input.

19. A system as claimed in claim 17 or 18, wherein the desired mode of operation is chosen from a first mode in which buffer size is increased, and a second mode in which buffer size is decreased.

20. A system as claimed in any one of claims 12 to 19, the encoder and transmitter unit to configure the transmission parameters using source rate adaptation.

21. A system as claimed in any of one of claims 12 to 20, wherein to encode a video datastream includes to encode, transcode, adapt or otherwise process the video datastream

22. A system as claimed in any one of claims 12 to 21, wherein the communications channel is a wireless communications channel.

23. A datastream transmission device to receive input data representing a mode of operation for the device; receive a video datastream to be transmitted;

select a set of parameters for transmission of the video datastream on the basis of the mode of operation:

modify the video datastream on the basis of the selected parameters; and transmit the modified video datastream over a communications channel.

24. A datastream transmission device as claimed in claim 23, wherein to modify the video datastream includes to encode, transcode, adapt or otherwise process the video datastream.

25. A datastream transmission device as claimed in claim 24, wherein to adapt the video datastream includes to select multiple portions of the video datastream to provide a substream to represent the video datastream with a reduced bit rate.

26. A datastream transmission device as claimed in any of claims 23 to 25, further including a channel estimator to:

estimate channel conditions of the communications channel, to allow the encoder further to use the estimated channel conditions in the selection of the parameters for transmission.