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1. 发明公开

EP0951779A1 IMPROVEMENTS IN OR RELATING TO SWITCHING BETWEEN COMPRESSED BITSTREAMS 失效
标题翻译：改进技术或与之相关的将压缩码流之间切换
公开(公告)号：EP0951779A1
公开(公告)日：1999-10-27
申请号：EP97950333.0
申请日：1997-12-24
申请人： NDS LIMITED
发明人： BOCK, Alois, Martin , DALLARD, Nigel, Stephen
IPC分类号： H04N7
CPC分类号： H04N21/23406 , H04N21/23424 , H04N21/23605 , H04N21/23608 , H04N21/26603 , H04N21/4343 , H04N21/4344 , H04N21/44004 , H04N21/44016
摘要： According to one aspect of the present invention, there is provided a method of switching from a first bitstream to a second bitstream, in a system having a decoder with a buffer through which the bitstream is transmitted, the method comprising: stopping the decoder from carrying out the decoding process in a predetermined manner at a predetermined point on the first bitstream, such that the buffer is substantially emptied; and restarting the decoder in a controlled manner at a predetermined position on the second bitstream, thereby switching from the first bitstream to the second bitstream. This invention allows insertion of additional programs, advertisements and the like into a standard MPEG stream without any of the disadvantages experienced using the hooks provided for in MPEG-2. One advantage of the proposed method is its simplicity. In terms of the MPEG-2 standard it requires intervention essentially only at the transport layer. The transport packet headers in MPEG-2 indicate the start of packets of elementary streams (PES packets). This flag is used for the control of all events in the switching process. The invention also allows for simple insertion of additional information in other types of bitstream.

2. 发明公开

EP0929976A1 METHOD AND APPARATUS FOR MOTION ESTIMATION 失效
标题翻译：用于运动估计的方法和设备
公开(公告)号：EP0929976A1
公开(公告)日：1999-07-21
申请号：EP97943960.0
申请日：1997-09-26
申请人： NDS LIMITED
发明人： BOCK, Alois, Martin
IPC分类号： H04N7
CPC分类号： H04N19/567 , H04N19/51
摘要： The present invention relates to a method of generating and transmitting digitally encoded signals in which portions of the code are predicted from earlier. The invention is applied to a digital video compression system in which temporal predictive coding is used in order to reduce the data rate of the transmitted signal. Predictions are made for the reconstruction of the current picture based on elements of pictures that have been coded in the past. A prediction is made for each reference block from each of five picture areas. A distortion value is derived for each prediction and a selection is made from the predictions based on the distortion values of the predictions. By biasing the selection between the different predictions towards that prediction which was last selected, predictions of approximately equal quality from completely different picture areas will be avoided. This avoids the situation where small advantages in prediction quality are outweighed by a larger codeword for the transmission of the prediction.
摘要翻译：本发明涉及一种产生和传输数字编码信号的方法，其中部分代码是从较早的时间预测的。本发明应用于数字视频压缩系统，其中使用时间预测编码以降低发送信号的数据速率。基于过去编码的图像元素对当前图像进行预测。对来自五个图片区域中的每一个的每个参考块进行预测。为每个预测导出失真值，并根据预测的失真值从预测中进行选择。通过在不同的预测之间偏向于最后选择的预测的选择，将避免来自完全不同图像区域的近似相等质量的预测。这避免了预测传输的较大代码字超过预测质量的小优点。

3. 发明公开

EP0940044A1 METHOD AND APPARATUS TO DETECT THE PRESENCE OF NOISE 失效
标题翻译：方法和设备噪声检测
公开(公告)号：EP0940044A1
公开(公告)日：1999-09-08
申请号：EP97940230.0
申请日：1997-09-08
申请人： NDS LIMITED
发明人： BOCK, Alois, Martin
IPC分类号： H04N17
CPC分类号： H04N17/00
摘要： The invention concerns a method and apparatus for detecting noise in an electrical signal. The invention is of particular application to the detection of noise in an electrical signal which represents an input video signal. The input signal is subjected to a frame delay and the absolute difference of each frame compared to the succeeding frame is derived by a difference circuit. The absolute difference signal from the difference circuit is sampled and the samples are applied to four comparator gates each of which selects samples having a signal level corresponding respectively to the gate. The outputs from the gates are counted in four accumulators which correspond respectively to the gates. The accumulated count values are supplied to a microprocessor which fits a probability density curve to the count values and determines whether a local maximum exists in the curve within a selected range of signal values. The presence of such a local maximum is indicative of the presence of noise in the input signal.

4. 发明公开

EP0903041A2 IMPROVEMENTS IN OR RELATING TO CHANGING THE BIT RATE OF A SIGNAL 失效
标题翻译：的改进比特率变化的信号
公开(公告)号：EP0903041A2
公开(公告)日：1999-03-24
申请号：EP97925140.0
申请日：1997-06-02
申请人： NDS LIMITED
发明人： BOCK, Alois, Martin
IPC分类号： H04N7
CPC分类号： H04N19/40 , G11B20/00007 , G11B20/10527 , H04N21/234345 , H04N21/2365 , H04N21/23655 , H04N21/4334 , H04N21/4347 , H04N21/440245 , H04N21/47208
摘要： The present invention relates to a method and apparatus for changing the bit rate of an input compressed digital signal such as a digitally compressed video signal including quantised picture information and motion vectors relating to motion compensation between picture frames. In order to change the bit rate of the signal, the present invention provides in a first step, for a partial decoding of the signal including a separation of a component including the motion vectors. In a second step, the quantisation of the quantised picture information is modified so as to change the compression of the picture information. In a third step, the modified picture information is reassembled with the motion vectors to generate an output video signal. The invention may be applied to a near video on demand (NVOD) in which the signal is multiplexed with time shifted versions of itself and the bit rate of the signal is changed such that the combined bit rate of the multiplexed signals is limited to a rate which can be accommodated by the multiplexer.

5. 发明公开

EP0906699A1 METHOD AND APPARATUS FOR PROCESSING A DIGITAL SIGNAL 失效
标题翻译：方法和装置处理的数字信号
公开(公告)号：EP0906699A1
公开(公告)日：1999-04-07
申请号：EP97924123.0
申请日：1997-05-29
申请人： NDS LIMITED
发明人： BOCK, Alois, Martin
IPC分类号： H04N7
CPC分类号： H04N21/23655 , H04N19/117 , H04N19/137 , H04N19/146 , H04N19/149 , H04N19/172 , H04N19/179 , H04N19/503 , H04N19/61 , H04N19/80 , H04N19/85
摘要： The present invention relates to a method and apparatus for analysing a digital video signal (20) preparatory to the digital compression encoding of the video signal. The signal (20) is applied to an analyser (22) to store samples of the video signal and to derive difference signals representing a number of parameters of the signal. One such parameter is the absolute difference between pixel samples of the signal which are adjacent in a vertical-temporal direction, i.e. the absolute difference between each sample and a sample one frame period later. Other parameters of the video signal are derived from absolute differences between the pixel samples taken over periods of one line, one field and one sample interval. A control signal representing the coding criticality of the input video signal is produced by accumulating the difference signals and combining them as a weighted sum. A low-pass filter in a pre-processor (21) has a bandwidth controlled by the control signal and filters the video signal (20) to remove or limit components which would result in coding artefacts in the signal after compression encoding. The control signal may also be fed to other components in the transmission chain, such as an encoder (23) and statistical multiplexer (24) to provide an early indication of picture criticality.

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