GB2438005A

GB2438005A - Transcoding compressed video and inserting graphics

Info

Publication number: GB2438005A
Application number: GB0609052A
Authority: GB
Inventors: Adrian Charles Paskins
Original assignee: Sony United Kingdom Ltd
Current assignee: Sony Europe Ltd
Priority date: 2006-05-08
Filing date: 2006-05-08
Publication date: 2007-11-14
Also published as: GB0609052D0

Abstract

A module 1 transcodes a compressed input video stream encoded by a first encoding scheme into a compressed output video stream encoded by a second encoding scheme. A decoder 19 performs decoding of the input video stream into an uncompressed video stream and an encoder 21 performs encoding of the uncompressed video stream into the output video stream. A graphics generator 25 generates graphics data representing graphics for display on the video images of the output video stream. The uncompressed video stream is supplied through insertion logic 22 which inserts the graphics data generated by the graphics generator into the uncompressed video stream. This facilitates insertion of graphics onto the video stream within the transcoder device 1 without the need to send external commands to cause insertion downstream of the transcoder device 1. Similar advantages are achieved in a DVB-CI module 40 which outputs an uncompressed video stream through a video interface 41.

Description

Video Stream Processing Device The present invention relates generally

to digital television, and the reception and decoding of video streams. In one aspect, it relates to transcoding of a compressed input video stream encoded by a first encoding scheme into a compressed output video stream encoded by a second encoding scheme. In another aspect, it relates to a module conforming with the DVB-CI standard.

When video streams are broadcast or transmitted as part of a digital television signal, the video streams are encoded to achieve compression and reduce the required bandwidth. To receive the transmitted or broadcast video streams, a digital television receiver included in a reception apparatus such as a television, a set-top box or an IP-TV tuner of a personal computer includes a decoder for decoding the compressed video stream which is received.

It is known to provide the reception apparatus with a module conforming with the DVB-CI standard (CENELEC EN50221) which includes a connector conforming with the PCMCIA standard. This allows the module to be connected to the PCMCIA slot which is commonly provided on a reception apparatus for receiving a radio frequency or satellite broadcast, for example a digital television or a set-top box.

Such a PCMCIA slot is provided with the main purpose of implementing the DVB-CI standard to allow the connection of a DVB-CI conditional access module (CAM) which can descramble scrambled content streams.

In accordance with the DVB-CI standard, the module includes a transport stream interface through which the compressed input and output video streams may be passed. The input transport stream, which contains the streams of video with audio and other data services, is received by the reception circuit of the reception apparatus to which the module is connected through the DVB Common Interface and then passed to the module. The module may then process the video stream, for example to descramble a scrambled video stream, and then return it to the reception apparatus.

Currently, the majority of digital television transmissions and broadcasts are encoded using MPEG-2 as the encoding scheme. However, as time progresses further encoding schemes are being developed and implemented to broadcast and transmit video streams. For example, currently there is increasing interest in and use of MPEG-4 as the encoding scheme. Unfortunately, the introduction of new encoding schemes makes the decoders of existing digital television receivers obsolete. This introduces expense both to manufacturers in the design of new products incorporating the decoders for the new encoding schemes and also to consumers in the purchase of new equipment including decoders for the new encoding schemes.

To tackle this problem, WO-2004/049 10 suggests provision of a transcoder device which performs transcoding of a compressed input video stream encoded by a new encoding scheme into a compressed output video stream encoded by a second encoding scheme which is the encoding scheme handled by legacy equipment. The output video stream is supplied to the legacy equipment and therefore adapts legacy equipment to allow reception of the input video stream encoded by the new encoding scheme without the need for modification of the legacy equipment itself. WO- 2004/049 10 suggests that the transcoder device might be formed in a module conforming with the DVB-CI standard.

There exists a problem in implementing a man-machine interface to allow control of a module in accordance with the DVB-CI standard. The DVB-CI standard includes a command interface being a bi-directional interface through which commands may be passed. To implement a man- machine interface, WO-2004/049 10 suggests that the module might transmit commands over the command interface to inform or query the user by display of information on the display connected to the reception apparatus. Similarly, the module may receive commands over the command interface in response to which the operation of the module is controlled.

Unfortunately, the command interface has only an 8-bit width and uses a slow push-pull style transfer protocol. These characteristics and the limited polling and buffering resources provided by most implementations of the command interface constrain the bandwidth. This in turn limits the speed of any interaction between the module and the host reception apparatus. In practice, this slow communication limits the effectiveness of applications on the module which utilise the command interface to provide interactivity with the user.

Implementation of a man-machine interface (MMI) is an example where the bandwidth limitations of the command interface cause a problem. The DVB-CI standard includes two MMI modes in which the module can utilise MMI resources on the reception apparatus to present an on-screen display on the video images of the uncompressed video stream output by the decoder in the reception apparatus. In particular when implementing the low-level MMI mode which provides the module with detailed control over the look of the on-screen display, the slow speed of communication over the command interface is a bottleneck which severely degrades the performance of the MMI as perceived by a user. In practical terms, this severely limits the ability to provide rich interactive services to the user, contrary to the trend that technological advances increase interactivity in the broadcast and transmission of video streams.

One could consider applying the transcoder device outside the context of a module in accordance with the DVB-CI standard to allow connection to a reception apparatus for receiving a radio frequency or satellite broadcast. In this case, the advantage of allowing adaption of legacy equipment to receive input video streams encoded by a new encoding scheme would still be achieved. However, there would remain problems of the type just discussed resulting from limitations on the communication between the transcoder device and the legacy equipment providing a bottleneck. This would in practical terms limit control of the legacy equipment by the transcoder device to insert graphics on the video images of the uncompressed video stream output by the decoder of the legacy equipment, for example to provide an on-screen display as part of an MM!.

According to a first aspect of the present invention, there is provided a transcoder device for transcoding a compressed input video stream encoded by a first encoding scheme into a compressed output video stream encoded by a second encoding scheme, the transcoder device comprising: a decoder arranged to perform decoding, in accordance with the first encoding scheme, of the input video stream into an uncompressed video stream; an encoder arranged to perform encoding, in accordance with the second encoding scheme, of the uncompressed video stream into the output video stream; a graphics generator arranged to generate graphics data representing graphics for display on the video images of the output video stream; insertion logic, through which insertion logic the uncompressed video stream is supplied from the decoder to the encoder, the insertion logic being arranged to insert the graphics data generated by the graphics generator into the uncompressed video stream.

The transcoder device may perform transcoding in the same manner as the device disclosed in WO-2004/04910 and therefore achieves the advantage of allowing adaption of legacy equipment including a decoder for an encoding scheme, that is the second encoding scheme, to a new encoding scheme, that is the first encoding scheme.

According to a second aspect of the present invention, there is provided a module conforming with the DVB-CI standard and comprising: a transport stream interface through which the module is capable of receiving a compressed input video stream encoded by a first encoding scheme; a command interface through which the module is capable of receiving commands, and a decoder arranged to perform decoding, in accordance with the first encoding scheme, of an input video stream received through the transport stream interface into an uncompressed video stream; a graphics generator arranged to generate graphics data representing graphics for display on the video images of the output video stream; and insertion logic arranged to insert the graphics data generated by the graphics generator into the uncompressed video stream supplied from the decoder, the module being arranged to output the uncompressed video stream from the insertion logic either without compression or after compression in the module.

The module may be a transcoder device further comprising an encoder so that the device may perform transcoding in accordance with the first aspect of the invention, in the same manner as the device disclosed in WO-2004/04910.

Alternatively, the module may output the uncompressed video stream having the graphics data inserted therein without compression through a video interface, for example an HDMI interface, a DVI interface or a component video interface.

Furthermore, both aspects of the present invention allow the transcoder device or module to cause display of graphics, for example providing an on-screen display, on the video images of the video stream. This is achieved without the need for the transcoder device or module to communicate with the legacy equipment to insert the graphics.

In the first aspect of the invention, the transcoder device takes advantage of the fact that the transcoding is performed by decoding and subsequently encoding the video stream passing through the device. Between the decoder and the encoder, the video signal is uncompressed. In the second aspect of the invention the module also takes advantage of the fact that an uncompressed video stream is present within the module.

This makes it straightforward to insert the graphics data in the transcoder device or module, in contrast to the normal situation handling compressed video streams where the compression makes it difficult to insert graphics data. The graphics are displayed on the video image output by the reception apparatus automatically with the normal decoding process of the downstream decoder so there is no additional processing load on the apparatus including the downstream decoder apparatus and there is no communication bottleneck which will slow modification of the graphics.

In some embodiments, the transcoder device or module includes a controller arranged to control the operation of the transcoder device, the transcoder device or module is capable of receiving commands indicating user-inputs, and the controller is arranged to control the graphics generator to generate graphics data providing an on-screen display and to control the operation of the transcoder device in response to the commands, for example so as to implement a man-machine interface.

With regard to the first aspect of the invention, a particularly advantageous application is for the transcoder device to be formed in a module conforming with the DVB-CI standard so that it is also in accordance with the second aspect of the invention. In this case, the module may be connected to a reception apparatus, for example a television, a recording apparatus, or a set-top box which includes a reception circuit for receiving a video stream from a radio frequency broadcast or a satellite broadcast. In this case, the input video stream is received by the reception circuit of the reception apparatus and passed to the transcoder device through the transport stream interface.

However the transcoder device may equally be applied to systems which receive video streams over other media. An important example is that the transcoder device may comprise a network interface for receiving data over a data network, the input video stream being input to the transcoder device through the network interface. In general, the data network may be any wired network or a wireless network. However, one advantageous implementation is that the network interface implements the Internet Protocol (IP) standard, so that the transcoder device may implement a receiver for IP-TV. Another advantageous implementation is that the data network is a wireless local area network, for example Wi-Fi.

According to further aspects of the present invention, there may be provided methods corresponding to the operation of the apparatuses in accordance with the first and second aspects, and also corresponding computer programs.

To allow better understanding, embodiments of the present invention will now be described by way of non-limitative example with reference to the accompanying drawings, in which: Fig. 1 is a diagram of a television having a DVB-CI module which is a transcoder device connected thereto; Fig. 2 is a diagram of the internal arrangement of the DVB-CI module which is a transcoder device; and Fig. 3 is a diagram of a system for receiving JPTV and supplying it to the transcoder device and the television; Fig. 4 is a diagram of a transcoder device having a USB interface; Fig. 5 is a diagram of a further DVB-CI module; and Fig. 6 is a diagram of a television having the DVB-CI module of Fig. 5 connected thereto.

Fig. 1 shows a module 1 which is a transcoder device connected to a television apparatus 2 which is legacy equipment with the capability of decoding MPEG-2 (which is the second encoding scheme in this example).

The television apparatus 2 is connected to an external antenna 3 in a conventional manner. The television apparatus 2 has a receiver circuit 4 which is supplied with a radio frequency television broadcast signal received by the antenna 3.

The broadcast signal contains video streams encoded by MPEG-4 (which is the first encoding scheme in this example) modulated onto a radio frequency carrier signal.

The video streams may be high definition (HD) video streams.

The receiver circuit 4 comprises an RF tuner 5 which extracts the desired broadcast signal and a demodulator 6 which demodulates the broadcast signal to extract a multiplexed signal of a single broadcast channel. As is conventional for broadcast digital television, each broadcast channel carries a multiplexed signal in which a plurality of video streams and associated audio and data streams, commonly referred to as services, are multiplexed together.

The television apparatus 2 has a decoding circuit 7 including a demultiplexer 8 capable of extracting one of the video streams from a received multiplexed signal and a MPEG-2 decoder 9 for decoding the video stream extracted by the demultiplexer 8 in accordance with MPEG-2. The MPEG-2 decoder 9 outputs an uncompressed video stream which is supplied to a display device 10 which displays the video images of the video stream.

As the television apparatus 2 is legacy equipment, the decoder 9 is capable of decoding MPEG-2 but is not capable of decoding MPEG-4. Accordingly, the television apparatus 2 by itself is incapable of receiving broadcast signals containing video streams encoded with MPEG-4. The module 1 adapts the television apparatus to solve this problem as follows.

The module I conforms with the DVB-CI standard. Accordingly, the module 1 has a PCMCIA connecter 11 conforming with the PCMCIA standard to allow it to connect to a PCMCIA slot 12 provided on the television apparatus 2. In order to allow connection of a Conditional Access Module (CAM) which can descramble scrambled video streams, it is very common for a television apparatus, and indeed for other types of reception apparatus, to be provided with an interface in accordance with the DVB-CI standard and including a slot in accordance with the PCMCIA standard. DVB-CI stands for Digital Video Broadcasting-Common Interface.

Fig. 2 shows the arrangement of the module 1. The module 1 includes a controller 13 which controls the operation of the components of the module 1. The controller 13 is implemented by a microprocessor running an appropriate program. In accordance with the DVB-CI standard, the module 1 further includes a transport stream interface 14 and a command interface 15.

The transport stream interface 14 which includes the PCMCIA connector 11 as part of the physical layer receives an input multiplexed signal 16 and transmits an output multiplexed signal 17, the input and output multiplexed signals commonly being referred to as transport streams. The television apparatus 2 is routed to supply the multiplexed signal from the receiver circuit 4 to the module 1 as the input multiplexed signal 16 and similarly to supply the output multiplexed signal 17 to the MPEG-2 decoding circuit 7.

The module 1 has a demultiplexer 18 which is supplied with the input multiplexed signal 16. The demultiplexer 18 demultiplexes the input multiplexed signal 16 and extracts one of the compressed video streams which is to be displayed on the display device 10, this constituting the input video stream in this example.

The module 1 has an MPEG-4 decoder 19 which is supplied with the input video stream. The MPEG-4 decoder 19 is arranged to perform decoding in accordance with MPEG-4. Accordingly, the MPEG-4 decoder 19 decodes the input video stream which is compressed by MPEG-4, into an uncompressed video stream.

The MPEG-4 decoder 19 includes a number of frame buffers 20 to store frames of the input video stream and the uncompressed video stream, as needed to perform decoding.

The uncompressed video stream is supplied from the MPEG-4 decoder 19 to an MPEG-2 encoder 21 through insertion logic 22 described further below.

The MPEG-2 encoder 21 is arranged to perform encoding of the uncompressed video stream in accordance with MPEG-2. Accordingly, the MPEG-2 encoder 21 encodes the uncompressed video stream into a compressed output video stream. Thus the MPEG-4 decoder 19 and the MPEG-2 encoder 21 together perform transcoding, so the module 1 operates as a transcoding device.

The MPEG-2 encoder 21 may encode the output video stream as a succession of I-frames only. I-frames are frames which contain spatial information of only a single video frame. By not using P-frames and B-frames which are predictive frames referring to video frames other than the current one, the buffering requirement of the MPEG-2 encoder 21 is significantly reduced and both the complexity and cost of the module I are correspondingly reduced. This is possible, because the hardwired connections through the transport stream interface 14 to the MPEG-2 decoder circuit 7 of the television apparatus 2 have a sufficiently high bandwidth to accommodate the output video stream without any P-frames or B-frames. That being said, in other implementations the MPEG-2 encoder 21 could include P-frames and B-frames in the output video stream.

The module 1 has a multiplexer 23 which is supplied with the output video stream from the MPEG-2 encoder 21. The multiplexer 23 is also supplied with the input multiplexed signal 16, through a buffer 24 which is used to synchronise the signals received at the multiplexer 23. The multiplexer 23 is arranged to multiplex the output video stream into the input multiplex 16 signal in place of the input video stream extracted by the demultiplexer 18. The resultant effect is that the input video stream encoded by MPEG-4 is replaced by the output video stream representing the same video images but encoded by MPEG-2. The multiplexed signal output by the multiplexer 23 is supplied as the output multiplexed signal 17 through the transport stream interface 14.

The insertion logic 22 is used to insert graphics data into the uncompressed video stream passing between the MPEG-4 decoder 19 and the MPEG-2 encoder 21.

As a result the graphics are present in the output video stream supplied from the MPEG-2 encoder 21 for display on the display device 10 of the television apparatus 2. This is achieved as follows.

The controller 13 of the module 1 implements a graphics generator 25 which is capable of generating graphics data representing graphics such as an on-screen display for inclusion on the video images of the output video stream. Of course, as an alternative to being implemented in software the graphics generator 25 could be implemented as a hardware component controlled by the controller 13.

The graphics data generated by the graphics generator 25 are supplied through a buffer 26 to the insertion logic 22. The insertion logic 22 inserts the graphics data onto the uncompressed video stream passing from the MPEG-4 decoder 19 to the MPEG-2 encoder 21. The insertion logic 22 may in one configuration simply replace pixels of the uncompressed video stream by pixels of the graphics data. In another configuration, the insertion logic 22 may mix the graphics data with the pixels of the uncompressed video stream so that the graphics appear translucent, such that the viewer perceives the original video image with the graphics overlaid in some locations. The graphics may appear at any location on the video image of the video stream. The timing of the operation of the insertion logic 22 is synchronised with the uncompressed video stream by the controller 13 to insert the graphics data on the desired pixels to display the graphics in the desired location. The graphics buffer 26 holds the graphics data for supply at the appropriate timing to the insertion logic 22.

Typically the uncompressed video stream is passed from the decoder 19 to the encoder 21 as a series of blocks divided from a frame of the video stream. This reduces the buffering requirement of the MPEG-2 encoder 21. In this case, the supply of graphics data from the graphics buffer 26 to the insertion logic 22 is synchronised with the flow of blocks.

The insertion logic 22 may be implemented by a hardware circuit.

Alternatively, the insertion logic 22 could be implemented in part or in whole by software in the controller 13.

The controller 13 uses the graphics as part of the implementation of a man-machine interface (MMT). In particular, the controller 13 causes the graphic generator to generate graphics data representing graphics in the form of an on-screen display which provides options to the user. For example, the on-screen display might include an electronic program guide (EPG) indicating programs or might include a menu of settings for the operation of the module 1.

To further implement the MMI, the controller 13 sends commands 34 through the command interface 15 to the television apparatus 2 to cause the television apparatus 2 to accept inputs from a user, typically using an infrared remote control unit 27. Responsive to user-inputs, the television apparatus 2 transmits commands 34 indicating the user-inputs to the module 1 through the command interface 15. Such commands 34 are received by the controller 13. Responsive to the commands, the controller 13 controls the operation of the module to implement the MMI. For example, where the MMI includes the display of an EPG, the user-inputs may indicate a selection of a particular program and, in response thereto, the controller 13 may control the operation of the demultiplexer 18 to extract the video stream of the program from the input multiplexed signal 16 as the input video stream.

As described above, the module 1 transcodes compressed video streams which are supplied as part of a radio frequency broadcast signal received by the receiver circuit 4 of the television apparatus 2. The module 1 may alternatively transcode video streams transmitted through a data network 28. To facilitate this, the module 1 includes a network interface 29 arranged to receive data over the data network 28 to extract a compressed video stream which is supplied as the input video stream to the decoder 19. The network 28 and the corresponding network interface 29 may be of any type including a wired network or a wireless network. The network interface 29 may include a stack of protocols to handle data transmitted over the data network 28 in different formats.

An important example is that the network 28 is the internet. In this case, the network interface 29 includes protocols such as TCP/IP for receiving video streams over the internet. This example allows the module 1 to receive 1P-TV.

Another important example of the network 28 is a wireless local area network (LAN) such as Wi-Fi. Fig. 3 shows a system for receiving IP-TV in which the network 28 is such a wireless LAN. In this system, a computer 30 receives a video stream transmitted over the internet 31 as an IP-TV transmission. The computer 30 passes the video stream to a wireless LAN transmitter 32 which transmits the video stream over the wireless LAN 28. In this case, the module 1 has an antenna 33 which receives the video stream from the wireless LAN 28 and passes it to the network interface 29 which includes a protocol for the wireless LAN 28. This is another useful implementation of the module 1 for receiving IP-TV.

Whilst the module 1 shown in Fig. 1 relates to an implementation in which the module 1 is a transcoder device, the same technique of inserting graphics in the module 1 may be applied in other types of module in accordance with the DVB-CI standard. As an example, the module 40 is shown in Fig. 5 and will now be described. The module 40 of Fig. 5 is a modified form of the module 1 of Fig. 2. The common components are given the same reference numerals and for brevity are not described again.

The module 40 is in accordance with the DVB-CI standard and is designed to receive a high definition (HD) video stream. Accordingly, the module 40 includes a transport stream interface 14, a demultiplexer 18, a network interface 29 and an MPEG-4 decoder 19 as described above. A compressed input video stream is received through the transport stream interface 14 or the network interface 29 and decoded by the MPEG-4 decoder 19 to form the uncompressed HD video stream.

The module 40 includes a graphics generator 25, a graphics buffer 26 and insertion logic 22 which operate to insert graphics as described above.

However, in contrast to the module 1 outputting a compressed output video stream through the transport stream interface, the module 40 is arranged to output an uncompressed HD video stream. In particular, the module 40 includes a video interface 41 which may be for example an HDMI interface, a DVI interface or a component video interface. The uncompressed HD video stream having the graphics data inserted thereon output from the insertion logic 22 is output from the module 40 through the video interface 41. -1 3-

As shown in Fig. 6, the television apparatus 2 also has a video interface 43 and a cable 42 connects the video interfaces 41 and 43. Through the cable 42, the uncompressed output video signal is supplied from the module 40 to the video interface 43 of the television apparatus 2, and then supplied to the display device 10 which displays the video images of the video stream.

Of course it is also possible to combine the features of the module I and the module 40.

Of course, the embodiments described above are merely examples of the present invention and numerous variations and alternatives are possible, including (but not limited to) the following.

Whilst Figs. 2 and 5 illustrate a particular implementation in hardware and software running on the controller 13, the various components of the module could be implemented to varying degrees in hardware and software. It has already been described that the insertion logic 22 can be implemented in software, but so also can other components such as the non-physical layers of the network interface 29, the transport stream interface 14 and the command interface 15, as well as the demultiplexer 18, the MPEG-4 decoder 19, the MPEG-2 encoder 21 and the multiplexer 23. As the graphics generator 25 and insertion logic 22 may be implemented

in software, the invention may be implemented as a software upgrade to an existing module, for example an existing module which already implements the other components illustrated in Fig. 2. The software upgrade may be stored on a computer-readable storage medium such as a memory or transmitted to the device over a network during which transmission it is represented by a carrier wave.

Whilst the module 1 described above relates to an implementation in which the first encoding scheme is MPEG-4 and the second encoding scheme is MPEG-2, in general the first and second encoding schemes could be any encoding schemes. In typical implementation, the first encoding scheme will have a higher compression ratio than the second encoding scheme, but this is not essential.

A bypass link may be provided to allow the video stream to pass through the module I or 40 without the insertion of graphics. The module may be operated in a bypass mode in which the uncompressed video stream passes through the bypass link. The bypass mode may be used when the video stream is being recorded so that the graphics do not appear on the recorded video stream. The bypass mode may operate in parallel with the insertion mode in which the uncompressed video stream is passed through the insertion logic, or may be switched on and off in response to detection of whether or not a recording device (eg a DVD recorder, a hard drive or a VCR) is in operation.

In the case that the network interface 29 is present, the module 1 could be dedicated to transcoding an compressed input video stream from the data network 28.

In this case the module 1 or 40 might not receive the input multiplexed signal 16.

Furthermore, the module 1 or 40 might supply the output video stream through a different form of connector such that the module 1 or 40 is not in accordance with the entire DYB-CI standard.

An example of such an alternative form of module 1 is shown in Fig. 4. In this example, the module 1 has, instead of the transport stream interface 14 and the command interface 15 in conformity with the DVB-CI standard, a USB interface 35 in accordance with the USB standard and including a USB connector 36 as part of the physical layer. The USB interface 35, in a time-multiplexed manner, (1) receives the input multiplexed signal 16 and supplies it to the demultiplexer 18, (2) transmits the output multiplexed signal 17 from the multiplexer 23 and (3) transmits commands 34 bidirectionally. The other components of the module 1 in this alternative form are the same as shown in Fig. 2 and described above, and so for brevity are not described again.

Where the module 1 is not in accordance with the DVB-CI interface, the compressed input and output video streams may be transmitted by themselves, that is not multiplexed with other video streams. In this case, the demultiplexer 18 and the multiplexer 23 may be omitted.

The television apparatus 2 in the above example is a type of reception apparatus. In general, the module 1 could be connected to any other type of reception apparatus, including a reception apparatus without a display device (e.g. a set-top box) and including a reception apparatus having a recording device (e.g. a DVD recording drive or a hard drive). Similarly, the reception apparatus could receive other types of broadcast signal besides a radio frequency broadcast signal, for example a satellite broadcast signal, or could receive signals over a data network.

Claims

Claims I. A transcoder device for transcoding a compressed input video

stream encoded by a first encoding scheme into a compressed output video stream encoded by a second encoding scheme, the transcoder device comprising: a decoder arranged to perform decoding, in accordance with the first encoding scheme, of the input video stream into an uncompressed video stream; an encoder arranged to perform encoding, in accordance with the second encoding scheme, of the uncompressed video stream into the output video stream; a graphics generator arranged to generate graphics data representing graphics for display on the video images of the output video stream; insertion logic, through which insertion logic the uncompressed video stream is supplied from the decoder to the encoder, the insertion logic being arranged to insert the graphics data generated by the graphics generator into the uncompressed video stream.

2. A transcoder device according to claim 1, the transcoder device including a controller arranged to control the operation of the transcoder device, and being capable of receiving commands indicating user-inputs, and the controller being arranged to control the graphics generator to generate graphics data representing graphics providing an on-screen display and to control the operation of the transcoder device in response to the commands.

3. A transcoder device according to claim 2, wherein the controller is arranged to control the graphics generator to generate the graphics data representing graphics providing the on-screen display and to control the operation of the transcoder device in response to the commands, so as to implement a man-machine interface.

4. A transcoder device according to claim 3, wherein the on-screen display includes an electronic programme guide, and the controller is arranged to control the graphics generator to generate the graphics data representing graphics providing the on-screen display and to control the operation of the transcoder device in response to the commands, so as to implement a man-machine interface allowing the user to select a video stream.

5. A transcoder device according to any one of the preceding claims, wherein the transcoder device is formed in a module having a connector conforming with the PCMCIA standard, the input video stream being input to the transcoder device through the connector and the output video stream being output from the transcoder device through the connector.

6. A transcoder device according to any one of the preceding claims, wherein the transcoder device is a module conforming with the DVB-CI standard and including a command interface through which the transcoder device is capable of receiving commands, and a transport stream interface through which the input video stream is input to the transcoder device and the output video stream is output from the transcoder device.

7. A transcoder device according to any one of the preceding claims, wherein the transcoder device has a USB interface conforming with the USB standard and through which the input video stream is input to the transcoder device and the output video stream is output from the transcoder device.

8. A transcoder device according to any one of the preceding claims, wherein the transcoder device comprises a network interface for receiving data over a data network, the input video stream being input to the transcoder device through the network interface.

9. A transcoder device according to claim 8, wherein the data network is a wired network or a wireless network.

10. A transcoder device according to claim 8 or 9, wherein the network interface implements the Internet Protocol standard.

11. A transcoder device according to claim 8 or 9, wherein the data network is a 12. A transcoder device according to any one of the preceding claims, wherein the first encoding scheme and the second encoding scheme are different.

13. A transcoder device according to claim 12, wherein the second encoding scheme has a higher compression ratio than the first encoding scheme.

14. A transcoder device according to claim 12 or 13, wherein the input video stream is a high definition video steam and the output video stream is a standard definition video stream.

15. A transcoder device according to any one of the preceding claims, wherein the second encoding scheme is MPEG-2.

16. A transcoder device according to claim 15, wherein the encoder performs encoding of the uncompressed video stream into the output video stream as a succession of I-frames only.

17. A transcoder device according to any one of the preceding claims, wherein the first encoding scheme is MPEG-4.

18. A transcoder device according to any one of the preceding claims, wherein the transcoder device is for receiving the input video stream multiplexed with other video streams as part of a multiplexed signal, and the transcoder device further comprises: a demultiplexer supplied with the multiplexed signal and arranged to extract the input video stream; and a multiplexer supplied with the output video stream from the encoder and arranged to multiplex the output video stream into the multiplexed signal in place of the input video stream.

19. A transcoder device according to any one of the preceding claims, the transcoder device including a controller arranged to control the operation of the transcoder device, the graphics generator being implemented as part of the controller.

20. A transcoder device according to any one of the preceding claims, further comprising a graphics buffer arranged to store the graphics data generated by the graphics generator and to supply the graphics to the insertion logic for insertion into the video stream.

21. A method of inserting graphics on the video images of a video stream, the method comprising: receiving a compressed input video stream encoded by a first encoding scheme; decoding, in accordance with the first encoding scheme, the input video stream into an uncompressed video stream; generating graphics data representing graphics for display on the video images of the uncompressed video stream; inserting the generated graphics data onto the uncompressed video stream; and encoding, in accordance with a second encoding scheme, the uncompressed video stream into a compressed output video stream.

22. A method of operating a transcoder device for transcoding a compressed input video stream encoded by a first encoding scheme into a compressed output video stream encoded by a second encoding scheme, which transcoder device comprises a decoder arranged to perform decoding, in accordance with the first encoding scheme, of the input video stream into an uncompressed video stream, and an encoder arranged to perform encoding, in accordance with the second encoding scheme, of the uncompressed video stream into the output video stream, the method comprising: generating graphics data representing graphics for display on the video images of the uncompressed video stream; inserting the generated graphics data onto the uncompressed video stream; and encoding, in accordance with a second encoding scheme, the uncompressed video stream into a compressed output video stream.

23. A computer program capable of operation by a transcoder device for transcoding a compressed input video stream encoded by a first encoding scheme into a compressed output video stream encoded by a second encoding scheme, which transcoder device comprises a decoder arranged to perform decoding, in accordance with the first encoding scheme, of the input video stream into an uncompressed video stream, and an encoder arranged to perform encoding, in accordance with the second encoding scheme, of the uncompressed video stream into the output video stream, the computer program being capable on execution of causing the transcoder device to operate in accordance with claim 22.

24. A computer-readable storage medium storing a computer program according to claim 23.

25. A carrier wave representing a computer program according to claim 23. -21 -

26. A module conforming with the DVB-CI standard and comprising: a transport stream interface through which the module is capable of receiving a compressed input video stream encoded by a first encoding scheme; a command interface through which the module is capable of receiving commands, and a decoder arranged to perform decoding, in accordance with the first encoding scheme, of an input video stream received through the transport stream interface into an uncompressed video stream; a graphics generator arranged to generate graphics data representing graphics for display on the video images of the output video stream; and insertion logic arranged to insert the graphics data generated by the graphics generator into the uncompressed video stream supplied from the decoder, the module being arranged to output the uncompressed video stream from the insertion logic either without compression or after compression in the module.

27. A module according to claim 26, the module including a controller arranged to control the operation of the module, and being capable of receiving commands indicating user-inputs, and the controller being arranged to control the graphics generator to generate graphics data representing graphics providing an on-screen display and to control the operation of the module in response to the commands.

28. A module according to claim 27, wherein the controller is arranged to control the graphics generator to generate the graphics data representing graphics providing the on-screen display and to control the operation of the module in response to the commands, so as to implement a man-machine interface.

29. A module according to claim 28, wherein the on-screen display includes an electronic programme guide, and the controller is arranged to control the graphics generator to generate the graphics data representing graphics providing the on-screen display and to control the operation of the module in response to the commands, so as to implement a man-machine interface allowing the user to select a video stream.

30. A module according to any one of claims 26 to 29, wherein the module further comprises a video interface for outputting uncompressed video streams, the module being arranged output the uncompressed video stream from the insertion logic without compression through the video interface.

31. A module according to claim 30, wherein the video interface is one of an HDMI interface, a DVI interface or a component video interface.

32. A module according to any one of claims 26 to 31, wherein each of the compressed input video stream and the uncompressed video stream is a high definition video stream.

33. A module according to any one of claims 26 to 32, wherein the first encoding scheme is MPEG-4.

34. A module according to any one of claims 26 to 33, wherein the module is for receiving the input video stream multiplexed with other video streams as part of a multiplexed signal, and the module further comprises a demultiplexer supplied with the multiplexed signal and arranged to extract the input video stream.

35. A module according to any one of claims 26 to 29, wherein the module is a transcoder device for transcoding the compressed input video stream encoded by the first encoding scheme into a compressed output video stream encoded by a second encoding scheme, the module further comprising: an encoder arranged to perform encoding, in accordance with the second encoding scheme, of the uncompressed video stream having the graphics data inserted therein into the output video stream, the module being arranged to output the output video stream through the transport stream interface.

36. A module according to claim 35, wherein the first encoding scheme and the second encoding scheme are different.

37. A module according to claim 36, wherein the second encoding scheme has a higher compression ratio than the first encoding scheme.

38. A module according to claim 36 or 37, wherein the input video stream is a high definition video steam and the output video stream is a standard definition video stream.

39. A module according to any one of claims 35 to 38, wherein the second encoding scheme is MPEG-2.

40. A module according to claim 39, wherein the encoder performs encoding of the uncompressed video stream into the output video stream as a succession of I-frames only.

41. A module according to any one of claims 35 to 40, wherein the first encoding scheme is MPEG-4.

42. A module according to any one of claims 35 to 41, wherein the module is for receiving the input video stream multiplexed with other video streams as part of a multiplexed signal, and the module further comprises: a demultiplexer supplied with the multiplexed signal and arranged to extract the input video stream; and a multiplexer supplied with the output video stream from the encoder and arranged to multiplex the output video stream into the multiplexed signal in place of the input video stream.

43. A module according to any one of claims 26 to 42, wherein the module comprises a network interface for receiving data over a data network, the input video stream being input to the module through the network interface.

44. A module according to claim 43, wherein the data network is a wired network or a wireless network.

45. A module according to claim 43 or 44, wherein the network interface implements the Internet Protocol standard.

46. A module according to claim 43, wherein the data network is a wireless local area network.

47. A module according to any one of claims 26 to 46, wherein the module includes a controller arranged to control the operation of the module, the graphics generator being implemented as part of the controller.

48. A module according to any one of claims 26 to 47, further comprising a graphics buffer arranged to store the graphics data generated by the graphics generator and to supply the graphics to the insertion logic for insertion into the video stream.

49. A method of operating a module conforming with the DVB-CI standard, which module comprises a transport stream interface through which the module is capable of receiving a compressed input video stream encoded by a first encoding scheme, and a decoder arranged to perform decoding, in accordance with the first encoding scheme, of an input video stream received through the transport stream interface into an uncompressed video stream, the method comprising: generating graphics data representing graphics for display on the video images of the uncompressed video stream; inserting the generated graphics data onto the uncompressed video stream.

50. A computer program capable of operation by a module conforming with the DVB-CI standard, which module comprises a transport stream interface through which the module is capable of receiving a compressed input video stream encoded by a first encoding scheme, and a decoder arranged to perform decoding, in accordance with the first encoding scheme, of an input video stream received through the transport stream interface into an uncompressed video stream, the computer program being capable on execution of causing the module to operate in accordance with claim 49.

51. A computer-readable storage medium storing a computer program according to claim 50.

52. A carrier wave representing a computer program according to claim 50.