FR2887107A1 - Video stream transmitting method for video surveillance system, involves sending request to store video stream at coordinator node and receiving selected virtual channel number from node, where request comprises identifier of source node - Google Patents

Abstract

The method involves sending a request for storing an initial video stream at a coordinator node, where the request comprises an identifier of a source node. A selected virtual channel number is received from the coordinator node. Data packets of the initial video stream are transmitted over the selected virtual channel, where the video stream constitutes a packet header (PH) and a record header (RH) that have an information representing the source node and the type of data to be transmitted. Independent claims are also included for the following: (1) a method for storing a video steam multiplexed over a transmission channel of a communication network (2) a method for reading a video stream among a set of stored and multiplexed video streams (3) a device for transmitting an initial video stream through a communication network (4) a device for storing a video steam multiplexed over a transmission channel of a communication network (5) a device for reading a video stream among a set of stored and multiplexed video streams (6) a data medium readable by a computer system and including computer program instructions for implementing a video steam transmitting method (7) a computer program stored in a data medium and having instructions for implementing a video steam transmitting method.

Description

The present invention relates to the transmission of an initial video stream

  intended to be multiplexed before storage in a communication network, storage of such a video stream and its reading after storage.

  It finds an application in the simultaneous transport of several initial video streams from different sources, such as video surveillance cameras respectively connected to different nodes of a communication network.

  Generally, a video surveillance system is implemented through a communication network dedicated to this application. It is already known to bypass the limitations of network transport and write data by sizing network capabilities to a level that is compatible with the CCTV application and by duplicating storage units to increase write capabilities.

  The implementation of the video surveillance application becomes more complex when the application is integrated into an existing network, not designed for it and unsuitable for such an application. This is the case, for example, of a home-type network comprising a plurality of nodes and in which each access point can not receive more than two initial data streams in a node of the network. In addition, the storage units generally used in this kind of network do not allow to simultaneously store more than two initial data streams.

  A known solution to circumvent these limitations is to multiplex the initial data streams on a common transmission channel, instead of transmitting them on separate channels. For example, US 6,731,097 discloses such transmission of multiplexed initial streams and their storage in a suitable storage unit. Thus, in US 6,731,097, a receiving unit receives a plurality of initial streams multiplexed on a common channel. Each multiplexed initial stream consists of an initial data stream and a header identifying the corresponding initial data stream. The receiving unit is comprised of a storage unit comprising a plurality of storage areas, a buffer memory, a storage information storage memory, a computing unit, and a data storage controller. For each multiplexed initial stream, the controller identifies the corresponding header and stores the demultiplexed data in an associated storage area. In this document, the initial data does not come from different sources that are connected to different nodes of the network and thus the data multiplexing is done centrally. In addition, in US 6,731,097, the data received from the network is demultiplexed before being stored in the thus associated storage area. This results in a demultiplexing operation that is systematic and costly implementation, the implementation of a memory describing the stored data and also a storage protocol matching the data with storage addresses.

  Furthermore, in document US Pat. No. 6,704,493, a system is described for receiving a plurality of signals of different types respectively, which converts said signals thus received into a digital signal of one and the same type, preferably compatible with one of the MPEG standards. Each signal is packaged independently of the other signals so processed. The header information contained in the packets identifies the original source. The packets of the set of signals are then multiplexed in a transport stream. The transport stream can then be stored and each initial stream constituting it can be played again. On the other hand, such a system makes it possible to re-read only one initial stream at a time without the possibility of forming and displaying a mosaic. The major limitation of the document US 6,704,493 is that on the one hand all initial flows converge to the same network node, which can create a bottleneck especially if the initial streams are transmitted before encoding and, secondly, all the encoding and re-encoding processes are centralized on the same processing device. This last point makes it necessary to define a processing device having significant computing capabilities.

  We also find the notions of multiplexed initial stream storage and replay of an initial stream among the initial streams multiplexed in US 6,788,882. This document proposes a Digital Video Recorder (DVR) system. Such a DVR system consists of a storage unit simultaneously receiving several multiplexed channels and a display unit. The display unit can extract a portion of the signal from one of the multiplexed channels. However again, the system can not generate a common stream forming a mosaic of initial video streams. In practice, the system of US 6,788,882 receives data from separate channels and can store them in a single file on the storage unit. In US 6,788,882, the headers for distinguishing each initial stream are inserted at the receiving system. Such an insertion has the disadvantage of affecting the cost in a particular receiver node of the network and generates additional extraction and decoding operations.

  The Applicant has posed the problem of circumventing the network transport and write limitations of the storage unit by multiplexing the initial video streams to be transmitted while overcoming the problems of the aforementioned devices of the state of the art.

  The present invention provides a solution to this problem.

  It relates to a method of transmitting an initial video stream through a communication network comprising a plurality of source nodes each connected to at least one source capable of transmitting an initial video stream consisting of a plurality of data packets. .

  According to a general definition of the invention, the method is implemented by a source node of the communication network and comprises the following steps: a) sending a request to store an initial video stream to a node of the predetermined network, called coordinator node, the request comprising at least one identifier of the source node; b) receiving from the coordinator node of a selected virtual channel number; and c) sending on the selected virtual channel, data packets of the initial video stream whose headers include at least information representative of the source node and the type of data to be transmitted.

  Such a method according to the invention makes it possible to circumvent the limits of the network and of the storage unit, in particular by dispersing the load of the operation of multiplexing the initial video streams through the network, in particular at the level of the source nodes and the storage unit. a coordinator node, instead of a particular receiver node as in the aforementioned prior art. The method according to the invention also makes it possible to transmit packets from different sources on the same network channel (here the selected virtual channel), which has the effect of multiplexing the packets in the network and to store them directly in the network. storage unit.

  According to one embodiment, the virtual channel number is determined by the coordinator node among all the available channels on the communication network.

  In practice, when the source node is not the first to send a storage request to the coordinator node, the selected virtual channel number is that which is determined following the first storage request.

  According to another aspect of the invention, the method further comprises the following steps prior to the step of sending a packet on the channel: 1) measuring a level of activity of the packet to be sent; 2) comparison of the level of activity thus measured at a level of activity of a previous packet; 3) in the event of a difference in the level of activity, insertion in the header of the packet to send information representative of the change of activity level; and 4) insertion in the header of the packet to be sent, information representative of the level of activity thus measured.

  Such a data packet header insertion representing a measured activity level and a change in the activity level makes it possible to have additional information on the transported data, which will then enable the data to be retrieved as a function of these informations.

  In practice, the initial video stream is previously coded in a scalable resolution format.

  Such a scalable format makes it possible to display the videos in several formats and, in particular, in the form of a simultaneous visualization of a subset (mosaic) of the initial video streams stored.

  In another embodiment, the header of the packet to be sent includes information representative of the level of scalability.

  The present invention also relates to a method of storing a plurality of initial video streams multiplexed on a transmission channel of a communication network, the initial video streams consisting of a plurality of data packets, the packets of data being transmitted on the transmission channel according to the transmission method referred to above.

  According to another aspect of the invention, the method comprises the following steps: i) reading the headers of the packets constituting the initial video streams; ii) updating an activity table comprising at least one association between the information of the source node and the information representative of the change of activity level of the corresponding packet; iii) associating a storage address of a packet with activity change information in the activity table; and iv) storing data packets on a storage unit. Such a storage method makes it possible to order the information so as to find it more easily during subsequent requests.

  The present invention also relates to a method for reading at least one initial video stream from among a plurality of multiplexed video streams and stored according to a storage method according to that referred to above.

  According to another aspect of the invention, the method comprises the following steps: 1. selecting a desired level of activity; He. determining the storage addresses of the corresponding data packets at the selected activity level; III. reading packets in the storage unit; and IV. displaying on the receiving device, video streams resulting from read packets.

  Thus, it is possible to perform queries on specific activity levels and to easily find the corresponding data.

  According to yet another embodiment, the reading method comprises, prior to the display step, a step of constructing a video stream forming a mosaic in the case where the read packets correspond to a plurality of initial video streams, the display of the initial video streams being then in the form of a mosaic.

  The present invention also relates to a device for transmitting an initial video stream through a communication network comprising a plurality of source nodes each connected to at least one source capable of transmitting an initial video stream consisting of a plurality data packets.

  According to another aspect of the invention, the transmission device comprises: transmission means for sending a request for storage of an initial video stream to a node of the network, called coordinator node, the request comprising at least one identifier said source node; receiving means for receiving from the coordinator node a chosen virtual channel number; - Transmitting means being able to send on the chosen virtual channel, data packets of the initial video stream whose header includes at least information representative of said source node and the type of data to be transmitted.

  According to one embodiment, the device further comprises: means for measuring the activity level of the data packet to be sent; means for comparing the level of activity thus measured with an activity level of a preceding data packet; suitable insertion means, in the event of a difference in activity level, to be inserted in the header of the data packet to be sent, information representative of the change in activity level and information representative of the level of activity as well as measured.

  The present invention also relates to a device for storing a plurality of initial video streams multiplexed on a transmission channel of a communication network, the initial video streams being constituted by a plurality of data packets, the packets data having been transmitted on the transmission channel, comprising: means for reading the headers of the data packets constituting the initial video streams; processing means for updating an activity table comprising at least one association between the information of the source node and the information representing the change of activity level of the corresponding packet; and associating a storage address of a data packet including activity change information in the activity table; and means for storing the data packets in a storage unit.

  The present invention also relates to a device 25 for reading at least one initial video stream from a plurality of multiplexed and stored video streams, comprising: means for selecting a desired level of activity; processing means for determining storage addresses of the data packets corresponding to the selected activity level; means for reading the data packets in the storage unit; and display means on the receiving device, video streams resulting from the data packets thus read.

  According to one embodiment, the reading device further comprises means for constructing a common video stream forming a mosaic in the case where the packets read correspond to a plurality of initial video streams, the display of the initial video streams being then under the shape of a mosaic.

  The present invention also relates to a device for creating a video stream representing a mosaic generated from a plurality of initial video streams, adapted to be transmitted on a single transmission channel in a communication network, comprising: means for obtaining a plurality of initial video streams, each previously coded according to a format in which an initial video stream is composed of a basic version and a complementary improvement version, which improves the basic version spatially and qualitatively to obtain the full-resolution version of the initial video stream, the basic version being composed of a set of segments each consisting of a header and a set of blocks taken by line on the images of the video stream corresponding initial; extraction means, according to a predetermined extraction order and as a function of the number of original video streams thus obtained, of segments of each of the basic versions of the original original video streams; and means for constructing a video stream forming a mosaic by insertion in the same extraction order of the extracted segments so as to obtain a decodable video stream by a decoder adapted to decode an original video stream.

  The present invention also relates to an information carrier readable by a computer system, possibly removable, totally or partially, in particular CD-ROM or magnetic medium, such as a hard disk or a floppy disk, or a transmissible medium, such as an electrical signal or optical system, characterized in that it comprises instructions of a computer program for carrying out a method mentioned above, when the program is loaded and executed by a computer system.

  Finally, a subject of the present invention is a computer program stored on an information medium, said program comprising instructions for implementing a method mentioned above, when this program is loaded and executed by a computer system. Other features and advantages of the invention will emerge in the light of the detailed description below and the drawings in which: FIG. 1 represents a communication network according to the invention; FIG. 2 schematically represents a simplified representation of the network of FIG. 1; FIG. 3A schematically represents a representation of spatial scalability; FIG. 3B represents the resynchronization markers; FIG. 4 represents a flowchart illustrating the steps of searching for an emission channel according to the invention; FIG. 5 represents the formatting of the data packets according to the prior art; FIG. 6 shows the packetization with insertion of a recording header according to the invention; FIG. 7 represents a flowchart illustrating the step of the end of recording according to the invention; FIG. 8 represents a flowchart illustrating the steps of the method of replaying a subset of flows according to the invention; FIG. 9 represents a flowchart illustrating the steps of the method for creating a mosaic according to the invention; FIG. 10 schematically represents certain elements of the network of FIG. 2, in which the processing of the level of activity of the initial video stream according to the invention has been added; FIGS. 11A and 11B represent diagrams respectively illustrating the level of activity of two sources; FIG. 12 represents a diagram illustrating the evolution over time of the writing of the address in the storage unit; FIG. 13 represents an activity diagram as implemented according to the present invention; FIG. 14 represents a flowchart illustrating the steps of the method of processing a packet according to the invention; FIGS. 15A and 15B show flow charts respectively illustrating the writing and reading in the storage unit; and FIG. 16 represents an equivalent diagram of a node of the network according to the invention.

  The description of the present invention is based on the MPEG-2 video coding standard described in ISO / IEC 13818-2. However, other equivalent standards such as MPEG-4 or H263 version 2 can also be used here.

  The MPEG-2 standard can be classified as a set of block-based hybrid video coding methods. This standard defines a basic syntax to which are added a number of optional modes with different objectives. Among these modes, a number is intended to increase the resistance of the bitstream.

  Other modes such as scalability have been developed in order to increase the efficiency of video transmission systems in the case of simultaneous transmissions to multiple users having different reception and decoding capabilities.

  In a hybrid predictive video coding scheme with block-based motion compensation and transform coding, each frame of a sequence is divided into blocks of fixed sizes (typically 8 * 8 pixels). Each block is then treated more or less independently. Hybrid designation means that each block is encoded with a combination of motion compensation and transform coding. Indeed, a block is initially predicted from a block of a previous image. The estimation of the position of the nearest block visually to the current block in the reference image is called motion estimation. The displacement between the reference block and the current block is represented by a motion vector. Motion compensation consists of predicting the current block from the reference block and the motion vector. The prediction error between the original block and the predicted block is encoded with a DCT (Discrete Cosine Transform) transformation, quantized and converted to binary code words using variable length codes (VLCs). The role of motion compensation is to use temporal correlations between successive images to increase compression. The DCT transformation, on the other hand, makes it possible to reduce the spatial correlations in the error blocks. After the DCT transformation and quantization, a majority of the high frequencies are reduced to 0. As the human visual system is not very sensitive to high spatial frequencies, the impact on the visual aspect remains low. The coefficients of the DCT transformation are zigzagged from low frequencies to high frequencies to form a first bit stream. The presence in this bitstream of many 0 is exploited by a variable length code (commonly implemented by a runlength coding) to reduce its size.

  The encoding mode in which the temporal prediction is successful and the bit rate generated by the prediction error remains lower than that of the original MB macroblock encoded without motion compensation, is generally called INTER mode.

  In some cases, the cost of the prediction error is too great. A DCT transformation and a runlength encoding are then applied directly to the block. This mode of coding is called INTRA mode. An image containing transformations MB inter is called image P. In practice motion estimation is very often applied to a set of blocks called macroblocks (MB) while the DCT transformation is applied to a block. The most common video encoders use 16 * 16 MB macroblocks. As the motion vectors of adjacent macroblocks MB are most often close, they can be coded predictively with respect to the already coded macroblocks MB.

  An image can be fully encoded in INTRA mode. This type of image is called INTRA or I. This type of coding is used for the first image of the sequence, but also to limit the propagation of the prediction and loss error or to allow functionalities such as access. random, fast forward or rewind ... The number of INTRA images is however generally limited to obtain better compression rates. The majority of the images of a sequence are thus coded in modes P. One does not forbid however to insert macroblocks MB INTRA in a picture P. In practice, the basic level of a scalable sequence is composed only of The quality of this level can be improved both temporally and spatially by using the various scalability modes defined in the standard. Three types of scalability are defined: spatial, temporal and SNR (quality of resolution: fine or coarse). Spatial scalability, as represented in FIG. 3A, is used here.

  Spatial scalability is about improving the quality of a lower level by adding spatial information. In general, this mode assumes that the base level NB has not been encoded at the resolution of the original sequence, but has instead under-sampled to divide its resolution by four (halving the horizontal and vertical dimensions). The coding of an image of a spatial NM enhancement level then begins with an interpolation of an NB base level image in order to recover the initial resolution. The difference between this image and the original image of the same size is then calculated. Then, several coding modes can be used for the MB macroblocks of the improvement image: the upward, forward and bidirectional modes.

  The upward mode consists in coding the difference using the same methods as for an intra image. However, the quantization parameter used for the improvement level is usually lower than the baseline. This ensures that in addition to improved spatial resolution, quality is improved. An image containing only macroblocks MB upward is called El (Enhancement Infra).

  Forward mode uses temporal prediction between images of the improvement level. An image containing a combination of MB forward and upward macroblocks is called EP. The encoding of an EP image also starts with interpolation of the base level image. A difference between the original image and the interpolated image is calculated. Two reference images are thus stored: the image of the extended base level and the image of the previous spatial improvement level (EI or EP). This last image is used to make a motion estimation in the current image. A motion vector is then obtained for each macroblock MB of the current image. After compensation of the reference image in motion, the upward and forward modes are compared for each macroblock MB. The mode that minimizes the difference between the original MB macroblock and the predicted MB macroblock is retained.

  In spatial scalability, other coding modes of MB macroblocks exist and can be used.

  The inter-image prediction methods have the side effect of increasing the fragility of video streams vis-à-vis the loss of data. For example, if a loss occurs in the bit stream of an image, the data following the loss is unusable since nothing allows the decoder to resynchronize. The header of the next image is then waited for to resume decoding.

  The resynchronization markers, also called segment headers (si / ce in English) were created to allow the decoder to resynchronize as soon as possible without waiting for the beginning of the next image.

  Thus, the segment is a set of macroblocks MB grouped behind a header. The macroblocks MB of a segment are decodable independently of the other macroblocks MB of an image. If a loss occurs in a segment, it can resume decoding the next segment received.

  The application described here is CCTV. However, other applications may be considered. In addition, the invention applies to any network having limited simultaneous transport and write capabilities and simultaneously receiving multiple analog video signals at different nodes of the network and storing them on a storage unit.

  Figure 1 shows a multimedia communication network installed, for example, in a home environment.

  The multimedia communication network may interconnect equipment such as individual television sets 103a, 103b and 103c, video recorders 107, DVD player type readers 108, a computer 112 and 111 individual cameras 111a, 111b, 111c and 111d. . It can also connect the analog output of a satellite decoder (not shown).

  According to the invention, the network comprises multimedia interface devices 150 also called network nodes or Network Adapter (NA) and individualized at 150a, 150b, 150c and 150d. The nodes 150 are connected to a central switching unit 160 called Switch preferably placed next to the electric power supply board.

  The node 150a is connected via an analog video link 105i to the television 103a. According to another preferred embodiment of the invention, the link 105i can be broadband and complies with the IEEE1394 standard. In this case, the TV has a corresponding IEEE1394 card.

  The node 150a is also connected via a link 130k according to the IEEE1394 standard to an analog digital converter 104a itself connected to a video recorder 107 via a link 106a.

  The analog TVs 103b, 103c and 103d are respectively connected to the nodes 150b, 150c and 150d identically to the link 105i connecting the analog television 103a and the node 150a.

  At node 150c is connected a computer 112 via an Ethernet type link 130n and / or an IEEE1394 link. The computer 112 can be replaced by a hard disk compatible with the IEEE1394 standard. In this case, it is connected to the multimedia interface via an IEEE1394 connection.

  The analog cameras 111a, 111b, 111c and 111d are connected to the nodes 150 via an Ethernet type link marked 130a.

  It should be noted that each of the nodes 150 comprises at least connection means of Ethernet, IEEE1394 and at least one analog video output. The multimedia interfaces 150 are connected to the switching unit 160 via single UTP CAT 5 cables individualized at 160a, 160b, 160c and 160d. The multimedia interfaces 150 are preferably based on the IEEE1394.1 standard for communicating multimedia devices through an IEEE1394 type serial bus network.

  Node 150 has a computing unit, a storage unit, an analog-to-digital converter encoding analog video streams in MPEG-2 format, and a digital-to-analog converter decoding MPEG-2 streams. It also has an infrared receiver capable of receiving infrared commands. Finally, it can implement a client request in the format http.

  In Figure 2, there is described a simplified representation of a network according to the invention. In this representation, there is the switching unit 160, three nodes NA here individualized at 150a, 150b, 150c, two cameras 111a and 111b and a digital hard disk 112 compatible with the IEEE1394 standard. A change in the number of cameras constituting this representation has no influence on the implementation of the invention.

  The two cameras 111 emit an initial video stream towards the disk 112 forming a storage unit. For example, the cameras 111 deliver an initial analog stream at the input of the nodes NA. The NA nodes then digitally encode these streams.

  The cameras may be digital cameras connected to the NA node with an IEEE1394 link. In this case, it is necessary to extract the digital video data from the IEEE1394 packets carrying them and to perform a transcoding of this data in the desired video format. Transcoding can consist simply of decoding the original digital video followed by re-encoding.

  The cameras 111 can also be analog. In this case, the NA nodes support the encoding of each sequence in MPEG-2 format. According to the preferred embodiment of the invention, this encoding is compatible with the main profile and the high level as defined in the MPEG-2 standard. Indeed, these levels and profiles allow the scalable encoding as described above.

  The images are encoded using spatial scalability as shown in Figure 3A. In addition, each image is encoded with si / these 5 SLs or segments (resynchronization markers) corresponding to macroblock lines MB (FIG. 3B). Using SL pacifiers of this form makes it easy to create a mosaic dataset when replaying multiple videos.

  In a second implementation, the analog videos may be encoded in a scalable format having more than two levels of spatial scalability NB and NM.

  This encoding can be supported in the nodes NA either by the digital analog conversion circuit, or in the form of a computer program stored in its storage unit and implemented by its computing unit.

  Before any data is sent to the storage unit 112, each node NA must identify on which channel its data must be sent. It is indeed necessary that all sources transmit on the same channel to perform the multiplexing operation.

  For the implementation of the invention, it is necessary for one of the nodes NA constituting the network to centralize the information on the simultaneous video recording applications. According to the preferred embodiment of the invention, this node NA is designated during installation of the network by the installer. This node NA, here called coordinator node, stores in its memory the number of nodes NA participating in a recording session and an identifier for each of these nodes NA. In addition, it searches among the available channels on the network, a free channel on which all sources or transmitters will have to emit. Finally, it receives and transmits requests to the other nodes NA. These queries are passed, for example, as http requests.

  The method of searching for a common virtual channel for the initial video streams is shown in Fig. 4 and starts at step E401. During this step the coordinating node NA, for example, the NAO node receives an http request from the source node NA, for example the node NA1. This request informs him that a new record must begin and issue him the identification number ID of the node NA1. The source node NA1 may be the coordinating node NA itself. This step is followed by the step E403 in which the coordinating node NA stores in its memory the identifier ID of the source node NA1. During the step E405, the coordinating node NA checks the current number of simultaneous records. If it is less than 0, step E405 is followed by step E421. During this step, the coordinating node NA selects a virtual channel from among all the virtual channels available on the network. This step is followed by step E411. Step E411 follows step E405 if the number of simultaneous recordings is greater than 0. In step E411 the number of simultaneous recordings is incremented by 1. If step E421 precedes step E411 , a registration table is created. It stores for each source, its identification number ID and the channel number on which it sends the data packets to be transmitted. If step E411 is preceded by step E405, the registration table is updated with the new source. Step E411 is followed by step E413 in which the coordinating node NA sends the source node NA1 as an http request the selected virtual channel number. The sending of data starts at step E417 upon receipt by the source node NA1 of the virtual channel number. The search process of the transmission channel ends in step E419.

  Step E417 relates to sending the data. For example, a particular method of packaging is used here. This is intended to facilitate the search for a video data stream in all flows stored on the storage unit.

  With reference to FIG. 5, the formatting of data packets according to the prior art is shown. In general, each data packet exchanged between a source node NA 150 and the switching unit 160 comprises a routing header OH, a packet header PH, an isochronous header 1394 IH, the packets DD data and an end-of-packet EOP indicator.

  The packet header PH comprises four fields CH1 to CH4. The field CH1 includes the identifier ID of the source, the field CH2 is a synchronization field, the field CH3 indicates the size of the packet and the field CH4 indicates the number of the channel.

  Compared to a conventional packet (shown in FIG. 5), an additional header called the record header HR is added according to the invention. With reference to FIG. 6, this record header RH contains three fields, individualized in Ti to T3: Ti: data type: this field identifies the nature of the data transported. According to the preferred embodiment of the invention, two types of data can be transported: the audio data and the video data.

  - T2: scalability level: this field indicates the level of scalability of the transported data. This field only applies to video data. It is not taken into account for the audio data. According to the preferred embodiment of the invention, this field takes the value 0 or 1. 0 indicates the basic scalability level NB. 1 indicates the level of improvement scalability NM.

  - T3: type of structure: this field indicates the type of the transported image. According to the preferred embodiment of the invention, an image can be of the type Infra (I), Inter (P), Bidirectional (B).

  If a source wishes to stop a recording, it sends in parallel to the last packet of its video an http request indicating the end of the recording and the identifier of the source NA node. This packet is received at step E701 shown in FIG. 7. This step is followed by the identification of the source of the request (step E703). This is followed by decrementing the number of records from 1 to step E704. If in step E705, the number of records is equal to 0, this step is followed by step E711 which deletes the corresponding contents of the registration table. Otherwise, step E705 is followed by step E707 which updates the registration table. Steps E707 and E711 end at the end step E709.

  Using a graphical interface, a user can request the replay of a subset of initial flows. The maximum number of replayable streams is set by the scalability level of the video. Here, we have chosen to break down the original video stream into two levels of spatial scalability. This implies that a user can only replay four streams simultaneously. The number of simultaneous replay can be increased by increasing the number of scalability levels.

  With reference to FIG. 8, the replay method according to the invention has been described. This method starts in step E801 by sending the user node NA a replay read record request. This http request contains the identifiers ID (at least one) of the sources that the user wishes to review. This step is followed by the step E803 which starts the replay of the initial stream multiplexed on the storage unit from the node NA on which it is connected (storage node NA). Step E805 reads the headers of each packet contained on the storage unit. This step is followed by the step E807 which reads the identifier ID of the source emitting this packet. Step E809 verifies that the packets sent by this source have been requested. If not, the packet is rejected in step E837. This step is followed by the step E833 which verifies that the storage unit contains other packets or that an http request terminating the replay has not been received. In the case of positive verification, the replay process ends in step E835. In case of negative verification, the process proceeds to the next packet in step E805.

  In the case of a positive verification in step E809, the method proceeds to step E811 in which the field Ti type of data contained in the header RH record header is read. If in step E813 it is detected that the packet does not contain video data, proceed to step E837. Otherwise, we go to step E815 which checks if a mosaic must be created. If the number of sources requested in the read record readback package is greater than 1, a mosaic dataset is created. If it is not, the packet is sent to the storage node NA in step E830. This packet is then transmitted to the node NA on which the user's display unit is connected in step E831. Step E831 is followed by step E833 already described.

  If the mosaic mode is started, step E815 is followed by step E817. During this step, the T2 scalability level is read in the HR header header of the packet. This step is followed by step E819 in which the level of scalability of the transported video data is verified. If these are not NB base level data, this step is followed by step E837. Otherwise, the process is continued with step E821. The packet is then sent to the storage node NA. In step E823, the video data of the packet is extracted. A mosaic image is created in step E825, by inserting the SL pacifiers constituting the image contained in the packet into a new MPEG-2 stream. This step is actually implemented when all SL slices required to create a mosaic image are received. As long as this is not the case if these SLs are stored in the memory of the node NA. This step is followed by step E827 which verifies that the mosaic image has been created. If this is not the case, the process proceeds to step E833. Otherwise, a new IEEE1394 packet is constituted in step E829 and sent to the display node NA in step E831 already described. The IEEE1394 package thus constituted does not contain an RH header header header.

  The procedure for creating the mosaic dataset is described with reference to FIG. 9. This procedure starts when the read record readback packet is received by the storage node NA and this packet indicates that several sources must be read simultaneously.

  This procedure starts in step E901 by writing the header of the mosaic sequence and the header of the first image of the sequence. This step is followed by the step E903 which initializes k to 0 and n to 1. The following step E905 tests if k = 4 in our exemplary embodiment where two scalability levels are provided, a mosaic being then composed of four videos. If this is the case, it means that a mosaic image has just been created and can be sent (one can answer yes to step E827 of FIG. 8). This step is followed by the step E923 in which the mosaic creation module waits for the reception of all the SLs / s needed for the next image to continue. As soon as they are received, the method writes the header of the next image in step E925 and the process returns to step E903. If the answer is negative in step E905, the process proceeds to step E907. This step checks that n has not reached the number of slices SL contained in an original image. If this is not the case, during step E911, reading in the memory of the node NA of the nth slice SL of the current image of the sequence k. This step is followed by writing the pacifier SL in the mosaic sequence in step E913. Then, during step E915, reading in the memory of the node NA nth pacifier of the current image of the sequence k + 1. This step is followed by the writing of the suck in the mosaic sequence in step E916 after the previous si / ce. n is incremented by 1 in step E917. Then return to step E907. If at this step, n equals NBslice, proceed to step E921. During this step k is incremented by 2. Step E921 is followed by step E919 which resets n to 1. Returning to step E905.

  The formation of a video stream forming a mosaic is more detailed in the French patent application filed on behalf of the Applicant on July 12, 2004, under number 0407753.

  Reference is now made to FIG. 10, in which certain elements of the network described with reference to FIG. 2 are found. For example, there are two cameras 111a and 111b connected to the home communication network through NAO network adapters. (150a) and NA1 (150b). The video content of each initial video stream is multiplexed and stored in the hard disk 112 connected to the network via the NA2 adapter (150c).

  All of the adapters are interconnected through the switching unit 160. All packets transmitted by the cameras 111 through a 1394 bus to the network adapters NA comprise an IH isochronous header and DD data in accordance with the IEEE1394 standards and IEC61883. The packets transmitted between each network adapter NA and the switching unit 160 further comprise a routing header OH, a packet header PH, a recording header RH as described with reference to FIG. 6 and an AH activity header. The AH activity header is used here for multiplex management and activity diagram purposes which will be described in more detail below. The AH activity header comprises five individualized fields A1 to A5. Fields A1 and A2 represent identifiers of the audio part. Field A3 represents an identifier of the video portion as defined in the MPEG2 standard. The A4 field refers to the activity level change and the A5 field refers to the activity level.

  Reference is now made to FIGS. 11A and 11B, in which diagrams illustrating respectively the level of activity of two distinct sources have been described. These diagrams show the evolution over time of the level of activity with respect to four levels: high, medium, low and normal.

  Referring to FIG. 12, there is shown a diagram representing the evolution over time of the writing of the address in the storage unit of the activity of a source whose level of activity over time is shown in Figure 11b. For this, the times of change of activity are mapped to the storage address of the beginning of the corresponding data in the storage unit.

  With reference to FIG. 13, the activity diagram as implemented according to the present invention is described. For example, the activity diagram is maintained in the node NA2, to which the storage unit 112 is connected. Each initial stream included inside a multiplex of several initial streams is referenced in a table according to an identifier ID. (300). Each initial stream corresponds to a storage address 302 and an activity level 301.

  In the event of detection of a change in the activity level for a given stream (for example, the activity change bit A4 is set to 1 in the corresponding A4 header), the write address of the beginning of the data corresponding to the change of activity, is stored in the table.

  Referring to Figure 14, there is shown a flowchart illustrating the steps of the method of processing a package according to the invention. In step E1400, after receiving a new packet from source 111, the device calculates the corresponding activity level (step E1401). The activity level calculation can be implemented by any method, for example, that of summing the absolute values of the interpixel differences between two images. This level of activity is quantified according to predefined or user-defined activity levels.

  According to the step E1402, the activity level is compared, for example with a threshold (idle threshold) which corresponds for example to the predefined or user-defined level corresponding to an irrelevant event activity. In the presence of a level of activity lower than said threshold, the algorithm returns to the initial state (step E1400) and the packet is not sent in the network for a recording in the storage unit. Such a selection saves storage resources by avoiding the storage of irrelevant information.

  In the case where the activity level is above the threshold, this activity level is compared to one of the values previously inserted in the previous packet (step E1403).

  In the presence of a level of activity identical to the previous one, the bit of change of activity A4 is set to 0, according to the step E1407 and the process proceeds to the step E1405.

  If the activity level A5 is different from the previous one, the activity change bit A4 is set to 1, step E1404 and the algorithm proceeds to step E1405.

  In step E1405, the activity level A5 is set to the current activity level value and the activity header AH contains this information which is inserted in the new packet, while the level of activity A5 current activity is stored as a previous activity level for subsequent comparison, in accordance with step El 408.

  Referring to Figs. 15A and 15B, the flowcharts illustrating write and read in the storage unit, respectively, have been described.

  Referring to Fig. 15A, when a new packet is received from the network according to step E1500, the activity header AH is analyzed according to step E1501. If the activity change bit A4 is at step E1502, the identifier ID of the corresponding initial stream is extracted from the activity header AH (step E1503) and the activity table is set. updated with the activity level value A5 and the corresponding write address in the storage unit (step E1504).

  The data packet is then stored in the storage unit at the write address value previously stored in the activity table (step E1505).

  If the activity change bit A4 is 0, there is no need to update the activity diagram and the method continues in step E1505.

  Referring to Figure 15B, the reading method in the storage unit has been described. The user, in a read request, defines an activity level threshold or a predefined activity level for which he wishes to display the flows whose activity level is greater than or equal to that requested.

  In response to a read access request at the storage unit level and initiated by a user in accordance with step E1506, the corresponding user-required A5 activity level is retrieved according to the step E1507 (for example, via the user interface) and the corresponding read address is chosen using the activity table (step E1508).

  The read mode access to the storage unit can be implemented at the previous reading address (read address in the activity table) for a better reading or display comfort.

  If more than one initial stream can be read at the same time (multiple video streams having the same level of activity), a mosaic stream (step E1509) is set up and sent across the network (steps E1510 and E1511) . If not, the stream thus read from the storage unit is sent through the network according to step El 511.

  With reference to FIG. 16, the equivalent diagram of a node of the network has been described.

  A node of the network comprises a gateway 1100 having connection capabilities for the IEEE1394 standard, via the serial bus 1106, as well as for the home communication network via the network interface 1101.

  The network controller 1102 is responsible for packetizing and transmitting / receiving data across the network. Buffers 1103 and 1104 are used respectively for sending and receiving data.

  A central unit 1105 is in charge of interfacing with another central unit 1120 to decode the registers of the central unit 1120 and to control the transfers with the SDRAM memory 1119 and the flash memory 1121.

  The audio / video module 1107 is responsible for packet formatting and deformatting the packet of the transport data stream transmitted on the IEEE1394 buses.

  The module 1107 bi-directionally communicates with the input / output ports 1111, 1112, 1113 via the MPEG encoders / decoders 1110, 1109, 1108.

  A controller 1114 controls the gateway 1100. The controller 1114 more particularly supports the following operations: - monitoring and management of operations in connection with the connection according to the IEEE1394 standard, including spying the incoming packets, generating the acknowledgments, managing the synchronous and asynchronous routing and synchronization of the clock; - request management and isochronous transfer between the 1394 interface and the home network interface on the one hand and the 1394 interface and the CPU interface on the other hand; - implementation of operations on header such as deletion, insertion of request, timestamping; receiving signals relating to the status of the interruption signals of the interface 1106; reception of the interface signals relating to the access signals of the interface of the bus 1106; - management of transmitted and received packets; - Analysis of the headers for the control of the insertion engine 1115 and the activity diagram manager 1123; and measuring and comparing activity level A5.

  The insertion engine 1115 is used to insert header data under the control of the controller 1114.

  Two FIFO-type stacks are also provided for transmission (FIFO 1117) and reception (FIFO 1116) respectively.

  The activity diagram manager 1123 generates and updates the activity table, as described with reference to the preceding figures in the case where the network node is a storage node.

  The mosaic generator 1124 generates the stream of mosaic packets.

  Thus, on the basis of an initial video stream, firstly multiplexed according to the protocols described above, in particular in FIG. 4 and intended to be transmitted through the network to be received at the level of a storage unit, an adapter NA network (here, NA1 when the source is the camera 111b, Figure 10) measures the activity level associated with the original video stream and inserts a tag (here an AH activity header) in each header of video packet thus conveyed through the network on a selected virtual channel. The other network adapters NA similarly send packets of data thus formatted through said virtual channel.

  On the basis of an initial multiplexed video stream transmitted through the virtual channel thus selected, a second network adapter (here NA2) connected to a storage unit (here the hard disk 112, FIG. 10) checks each header of received packet and updates the associated activity diagram before writing said packet into the storage unit.

  On the basis of a request from a user to access video content thus recorded, the network adapter (here NA2) checks the activity diagram, determines the value of the read address needed for access to the storage unit 112 and filters the data to be read in accordance with the required level of activity accompanying the request of the user.

  The network adapter (here NA1) can also filter the data according to a threshold defining a minimum level of activity below which no data is transmitted. Such a threshold can be statically defined using the background noise of the camera or by the user. This results in an optimization of the load capacity of the network as well as storage resources.

Claims (20)

  A method of transmitting an initial video stream through a communication network comprising a plurality of source nodes (150) each connected to at least one source (111) capable of transmitting an initial video stream consisting of a plurality data packets, characterized in that the method is implemented by a source node (150) and comprises the following steps: a) sending a request to store an initial video stream to a node of the network, called a node coordinator, the request comprising at least one identifier (ID) of said source node (150); b) receiving from the coordinator node of a chosen virtual channel number; c) sending on the chosen virtual channel data packets of the initial video stream whose headers (PH, RH) comprise at least information representative of said source node (PH, CHI, CH2, CH3, CH4) and of the type data to be transmitted (RH, Ti, T2, T3).   2. Method according to claim 1, characterized in that the virtual channel number (CH4) is determined by the coordinator node among all the available channels on the communication network.   3. Method according to claim 2, characterized in that when the source node is not the first to send a storage request to the coordinator node, the virtual channel number (CH4) selected is that which is determined as a result of the first storage request.   4. Method according to one of claims 1 to 3, characterized in that it further comprises the following steps prior to the step of sending a data packet on the virtual channel thus selected: 1) measuring the activity level (A5) of the data packet to be sent; 2) comparing the activity level (A5) thus measured at an activity level (A5) of a previous data packet; 3) in case of difference (A4) activity level, insertion in the header of the data packet to send (AH), information representative of the change (A4) level of activity; and 4) inserting into the header of the data packet to be sent (AH), representative information (A5) of the activity level thus measured.   5. Method according to one of claims 1 to 4, characterized in that the initial video stream is previously encoded in a resolution scalable format.   6. Method according to claim 5, characterized in that, in the case where the source is digital, the initial video stream undergoes transcoding at the source node to be coded in scalable resolution format.   7. The method of claim 5, characterized in that, in the case where the source is analog, the initial video stream is encoded at the source node to obtain a resolution scalable format.   8. Method according to one of claims 5 to 7, characterized in that the header (RH, T1, T2, T3) of the data packet to be sent comprises information representative of the scalability level of the initial video stream.   A method of storing a plurality of initial multiplexed video streams on a transmission channel of a communication network, the initial video streams being made up of a plurality of data packets, the data packets having been transmitted on the transmission channel according to a method according to one of claims 4 to 8, characterized in that it comprises the following steps: i) reading the headers (PH, AH, RH) data packets constituting the initial video feeds; ii) updating an activity table comprising at least one association between the information of the source node (PH, CH1, CH2, CH3, CH4) and the information representative of the activity level change (A4) the corresponding package; iii) associating an address (302) for storing a data packet including activity change information (301) in the activity table; and iv) storing the data packets in a storage unit (112).   10. A method of reading at least one video stream among a plurality of video streams multiplexed and stored according to a method according to claim 9, characterized in that it comprises the following steps: 1. selecting a level of desired activity (A5); He. determining the storage addresses of the corresponding data packets at the selected activity level; III. reading the data packets in the storage unit (112); 20 and IV. display on the receiving device, resulting video streams of data packets read.   11. The method of claim 10, characterized in that it comprises prior to the display step a step of building a common video stream forming a mosaic in the case where the read packets correspond to a plurality of video streams initially, the display of the initial video streams being then in the form of a mosaic.   12. Method according to claim 11, characterized in that the construction of a video stream forming a mosaic comprises the following steps: i) obtaining a plurality of initial video streams previously coded each according to a format in which an initial video stream consists of a basic version (NB) and at least one complementary enhancement version (NM) that improves the basic version (NB) spatially and qualitatively to obtain the full-resolution version of the original video stream, the versions base (NB) and enhancement are composed of a set of segments (SL) each consisting of a header and a set of blocks taken per line on the images of the corresponding initial video stream; ii) extracting, according to a predetermined extraction order and as a function of the number of initial video streams thus obtained, segments of at least each of the basic versions of the initial video streams obtained; and iii) constructing a video stream forming a mosaic by insertion in the same extraction order of the extracted segments so as to obtain a decodable video stream by a decoder adapted to decode an initial video stream.   13. Device for transmitting an initial video stream through a communication network comprising a plurality of source nodes each connected to at least one source capable of transmitting an initial video stream consisting of a plurality of data packets, characterized in that the source node comprises: transmission means for sending a request for storage of an initial video stream to a node of the network, called coordinator node, the request comprising at least one identifier of said source node; receiving means for receiving from the coordinator node a chosen virtual channel number; the transmission means being able to send on the chosen virtual channel, data packets of the initial video stream whose headers (PH, RH) comprise at least information representative of said source node (PH, CHI, CH2, CH3 , CH4) and the type of data to be transmitted (RH, Ti, T2, T3).   14. Device according to claim 13, characterized in that it further comprises: means for measuring the activity level (A5) of the data packet to be sent; means for comparing the activity level (A5) thus measured at an activity level (A5) of a preceding data packet; suitable insertion means, in the event of a difference in activity level, to insert in the header (AH) of the data packet to be sent, information (A4) representative of the activity level change and information (A5) representative of the level of activity thus measured.   15. A device for storing a plurality of initial video streams multiplexed on a transmission channel of a communication network, the initial video streams consisting of a plurality of data packets, the data packets having been transmitted on the transmission channel by at least one device according to claim 12 or 13, characterized in that it comprises: means for reading the headers of the data packets constituting the initial video streams; processing means for updating an activity table comprising at least one association between the information of the source node (PH, CH1, CH2, CH3, CH4) and the information representative of the change (A4) the activity level of the corresponding packet; and associating a storage address (302) of a data packet including activity change information (301) in the activity table; and - means for storing the data packets in a storage unit (112).   16. Device for reading at least one initial video stream from a plurality of video streams multiplexed and stored by a storage device according to claim 15, characterized in that it comprises: means for selecting a level desired activity (A5); processing means for determining storage addresses (302) of data packets corresponding to the selected activity level (A5); means for reading the data packets in the storage unit (112); and display means on the receiving device, video streams resulting from the data packets thus read.   17. Device according to claim 16, characterized in that it further comprises means for constructing a common video stream forming a mosaic in the case where the packets read correspond to a plurality of initial video streams, the display of initial video streams are then in the form of a mosaic.   18. Device according to claim 17, characterized in that the means for creating a video stream forming a mosaic comprise: means for obtaining a plurality of initial video streams, previously coded each according to a format in which a stream initial video consists of a basic version (NB) and at least one complementary enhancement version (NM), which improves the basic version (NB) spatially and qualitatively to obtain the full resolution version of the initial video stream , the basic (NB) and enhancement versions being composed of a set of segments (SL) each consisting of a header and a set of blocks taken per line on the images of the corresponding initial video stream; extraction means, according to a predetermined extraction order and as a function of the number of original video streams thus obtained, of segments of at least each of the basic versions of the original original video streams; and insertion means in the same extraction order of the extracted segments so as to construct a video stream forming a decodable mosaic by a decoder adapted to decode an original video stream.   19. Information medium readable by a computer system, possibly removable, totally or partially, in particular CD-ROM or magnetic medium, such as a hard disk or a floppy disk, or transmittable medium, such as an electrical or optical signal, characterized in that it comprises instructions of a computer program for carrying out a method according to any one of claims 1 to 12, when this program is loaded and executed by a computer system.   20. Computer program stored on an information medium, said program comprising instructions for implementing a method according to any one of claims 1 to 12, when the program is loaded and executed by a computer system. .