GB2557617A - Method and device for managing video streams in a video surveillance system - Google Patents

Method and device for managing video streams in a video surveillance system Download PDF

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Publication number
GB2557617A
GB2557617A GB1621086.6A GB201621086A GB2557617A GB 2557617 A GB2557617 A GB 2557617A GB 201621086 A GB201621086 A GB 201621086A GB 2557617 A GB2557617 A GB 2557617A
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Prior art keywords
video
video stream
surveillance system
request
source flow
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GB1621086.6A
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GB201621086D0 (en
Inventor
Visa Pierre
Sevin Julien
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Canon Inc
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Canon Inc
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Priority to GB1621086.6A priority Critical patent/GB2557617A/en
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N7/00—Television systems
    • H04N7/18—Closed-circuit television [CCTV] systems, i.e. systems in which the video signal is not broadcast
    • G—PHYSICS
    • G08—SIGNALLING
    • G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
    • G08B13/00—Burglar, theft or intruder alarms
    • G08B13/18—Actuation by interference with heat, light, or radiation of shorter wavelength; Actuation by intruding sources of heat, light, or radiation of shorter wavelength
    • G08B13/189—Actuation by interference with heat, light, or radiation of shorter wavelength; Actuation by intruding sources of heat, light, or radiation of shorter wavelength using passive radiation detection systems
    • G08B13/194—Actuation by interference with heat, light, or radiation of shorter wavelength; Actuation by intruding sources of heat, light, or radiation of shorter wavelength using passive radiation detection systems using image scanning and comparing systems
    • G08B13/196—Actuation by interference with heat, light, or radiation of shorter wavelength; Actuation by intruding sources of heat, light, or radiation of shorter wavelength using passive radiation detection systems using image scanning and comparing systems using television cameras
    • G08B13/19654—Details concerning communication with a camera
    • G08B13/19656—Network used to communicate with a camera, e.g. WAN, LAN, Internet
    • G—PHYSICS
    • G08—SIGNALLING
    • G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
    • G08B13/00—Burglar, theft or intruder alarms
    • G08B13/18—Actuation by interference with heat, light, or radiation of shorter wavelength; Actuation by intruding sources of heat, light, or radiation of shorter wavelength
    • G08B13/189—Actuation by interference with heat, light, or radiation of shorter wavelength; Actuation by intruding sources of heat, light, or radiation of shorter wavelength using passive radiation detection systems
    • G08B13/194—Actuation by interference with heat, light, or radiation of shorter wavelength; Actuation by intruding sources of heat, light, or radiation of shorter wavelength using passive radiation detection systems using image scanning and comparing systems
    • G08B13/196—Actuation by interference with heat, light, or radiation of shorter wavelength; Actuation by intruding sources of heat, light, or radiation of shorter wavelength using passive radiation detection systems using image scanning and comparing systems using television cameras
    • G08B13/19663—Surveillance related processing done local to the camera
    • G—PHYSICS
    • G08—SIGNALLING
    • G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
    • G08B13/00—Burglar, theft or intruder alarms
    • G08B13/18—Actuation by interference with heat, light, or radiation of shorter wavelength; Actuation by intruding sources of heat, light, or radiation of shorter wavelength
    • G08B13/189—Actuation by interference with heat, light, or radiation of shorter wavelength; Actuation by intruding sources of heat, light, or radiation of shorter wavelength using passive radiation detection systems
    • G08B13/194—Actuation by interference with heat, light, or radiation of shorter wavelength; Actuation by intruding sources of heat, light, or radiation of shorter wavelength using passive radiation detection systems using image scanning and comparing systems
    • G08B13/196—Actuation by interference with heat, light, or radiation of shorter wavelength; Actuation by intruding sources of heat, light, or radiation of shorter wavelength using passive radiation detection systems using image scanning and comparing systems using television cameras
    • G08B13/19665—Details related to the storage of video surveillance data
    • G08B13/19669—Event triggers storage or change of storage policy
    • G—PHYSICS
    • G08—SIGNALLING
    • G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
    • G08B13/00—Burglar, theft or intruder alarms
    • G08B13/18—Actuation by interference with heat, light, or radiation of shorter wavelength; Actuation by intruding sources of heat, light, or radiation of shorter wavelength
    • G08B13/189—Actuation by interference with heat, light, or radiation of shorter wavelength; Actuation by intruding sources of heat, light, or radiation of shorter wavelength using passive radiation detection systems
    • G08B13/194—Actuation by interference with heat, light, or radiation of shorter wavelength; Actuation by intruding sources of heat, light, or radiation of shorter wavelength using passive radiation detection systems using image scanning and comparing systems
    • G08B13/196—Actuation by interference with heat, light, or radiation of shorter wavelength; Actuation by intruding sources of heat, light, or radiation of shorter wavelength using passive radiation detection systems using image scanning and comparing systems using television cameras
    • G08B13/19678—User interface
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N21/00—Selective content distribution, e.g. interactive television or video on demand [VOD]
    • H04N21/20—Servers specifically adapted for the distribution of content, e.g. VOD servers; Operations thereof
    • H04N21/23—Processing of content or additional data; Elementary server operations; Server middleware
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N21/00—Selective content distribution, e.g. interactive television or video on demand [VOD]
    • H04N21/20—Servers specifically adapted for the distribution of content, e.g. VOD servers; Operations thereof
    • H04N21/23—Processing of content or additional data; Elementary server operations; Server middleware
    • H04N21/239—Interfacing the upstream path of the transmission network, e.g. prioritizing client content requests
    • H04N21/2393—Interfacing the upstream path of the transmission network, e.g. prioritizing client content requests involving handling client requests
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N21/00—Selective content distribution, e.g. interactive television or video on demand [VOD]
    • H04N21/40—Client devices specifically adapted for the reception of or interaction with content, e.g. set-top-box [STB]; Operations thereof
    • H04N21/43—Processing of content or additional data, e.g. demultiplexing additional data from a digital video stream; Elementary client operations, e.g. monitoring of home network or synchronising decoder's clock; Client middleware

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  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Signal Processing (AREA)
  • Human Computer Interaction (AREA)
  • Two-Way Televisions, Distribution Of Moving Picture Or The Like (AREA)
  • Closed-Circuit Television Systems (AREA)

Abstract

A method for managing video streams in a video surveillance system comprises receiving a request 400 from a first device of the video surveillance system, the request concerning a first video stream which is based on a source flow generated by a video camera. A second device of the video surveillance system simultaneously receives a second video stream which is also based on the source flow. A video stream configuration for at least one of the first device and second device is then selected 409, the selection being based on the request, on the current use of the source flow and on resource constraints of the system. The resource constraints may include: maximum streams permissible for transmission, device processing capability, memory storage capacity and network bandwidth. A plurality of possible configurations may be determined, classified according to how close they are to a devices required characteristics and the most appropriate configuration may be selected. The devices required characteristics may include: intended use, level of detected motion, image resolution, Peak Signal to Noise Ratio and maximum processing cost. The devices may be display, recording or processing devices.

Description

(54) Title of the Invention: Method and device for managing video streams in a video surveillance system Abstract Title: Managing video streams in a video surveillance system (57) A method for managing video streams in a video surveillance system comprises receiving a request 400 from a first device of the video surveillance system, the request concerning a first video stream which is based on a source flow generated by a video camera. A second device of the video surveillance system simultaneously receives a second video stream which is also based on the source flow. A video stream configuration for at least one of the first device and second device is then selected 409, the selection being based on the request, on the current use of the source flow and on resource constraints of the system. The resource constraints may include: maximum streams permissible for transmission, device processing capability, memory storage capacity and network bandwidth. A plurality of possible configurations may be determined, classified according to how close they are to a device’s required characteristics and the most appropriate configuration may be selected. The device’s required characteristics may include: intended use, level of detected motion, image resolution, Peak Signal to Noise Ratio and maximum processing cost. The devices may be display, recording or processing devices.
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METHOD AND DEVICE FOR MANAGING VIDEO STREAMS IN A VIDEO SURVEILLANCE SYSTEM
FIELD OF THE INVENTION
The present invention relates in general to video surveillance systems. In particular, the present invention provides a method for managing video streams in a video surveillance system. The present invention also provides a corresponding device and a video surveillance system.
BACKGROUND OF THE INVENTION
Video surveillance systems are increasingly numerous and are used for many applications such as crime prevention, industrial processes monitoring and traffic management.
Conventional video surveillance systems comprise one or more video cameras each capturing raw video data (hereafter called “source flows”) that are encoded as video streams and sent to device(s) for display, recording (e.g. for postevent investigation) and/or video content analytics (VCA) processing such as image analysis for face detection/recognition or object/people tracking.
Generally speaking, the characteristics (e.g. image resolution, frame rate, video encoding algorithm, compression rate) of encoded video streams typically depend on the target application (or intended use) of the source flows.
For instance, a VCA server may need a video stream having a high pixel resolution, a low video compression and a low frame rate while a display device may need a video stream having a resolution adapted to the size of the image displayed on the screen.
Document US 2015/201198 describes a system for video streaming of multiple encodings of video streams (from what is called a same “source flow”).
However, this document does not address several problems that may occur when several devices concurrently use the same source flow captured by the same video camera.
A first issue is that the number of video streams that can be simultaneously encoded based on a given source flow is generally limited to a few. Unfortunately, this limitation cannot always be overcome by broadcasting the same video stream to several devices, as devices may target different applications (e.g. display and processing) requiring different characteristics of the video stream or even they target the same application but with different requirements (e.g. display with different windows sizes thus different resolutions).
Another issue is that the source flow is encoded based on the requirements indicated by the devices while there are enough resources notably in terms of data processing (to decode video streams), data storage and available network bandwidth. Thus, for instance if a device requests a video stream requiring a high processing power, a large memory space for storage and a large network bandwidth for transmission, there may not be enough resources to transmit, store or decode other video streams.
Also, these requirements may change over time depending on the wishes of the operator of the device. For illustration purposes, the operator of a display device may first require a first video stream (from a first video camera) adapted to be displayed on a full screen having a given size and later, a second video stream from a second video camera to be displayed together with the first one on said screen. Since the screen will be shared between the two video streams, the first video stream will be displayed in a window having a smaller size. Hence, the current resolution of the first video stream is over-dimensioned, thereby preventing another device from benefiting from resources unnecessarily used.
Therefore, there is a need for improving existing methods of managing the video streams in a video surveillance system. There is also a need for improving the management of video streams in situations where several devices request video streams encoded from the same source flow.
SUMMARY OF THE INVENTION
The present invention has been devised to address one or more of the foregoing concerns.
In this context, according to a first aspect of the invention, there is provided a method for managing video streams in a video surveillance system comprising a plurality of devices, the method comprising:
receiving a request from a first device of the video surveillance system, the request concerning a first video stream which is based on a source flow generated by a video camera, a second device of the video surveillance system receiving a second video stream which is based on said source flow;
selecting a video stream configuration for at least one of the first device and the second device, said selecting being based on the request, on the current use of said source flow generated by the video camera and on resource constraints of the video surveillance system.
Thanks to embodiments of the invention, a good compromise is achieved between the requirements of the requesting device (“first device”) with regard to the current use of this source flow by other device(s) (“second device”) and the resource constraints of the video surveillance system.
This is because the video stream configuration of the stream that is or will be received by the requesting device and/or other device(s) currently using the source flow is adapted depending on the requirements of the devices (notably in the request from the first device) and on the resource constraints.
Thanks to this, if the first device requests the use of the source flow while this source flow is currently used by other device(s), the video stream configurations of the streams that are or will be received by at least some of these devices may be adapted to better share the resources while best meeting the requirements of these devices.
Also thanks to the first aspect aforementioned, if the first device requests the termination of the first video stream, the second device(s) currently using the source flow (or other devices) can benefit from the released resources.
Optional features of the invention are further defined in the dependent appended claims.
According to embodiments, the request is for receiving the first video stream (i.e. the first video stream is a new stream to be created), for modifying the first video stream or for terminating the transmission of the first video stream.
According to embodiments, the request indicates a set of characteristics required for the first video stream.
Generally, when an operator modifies the use of a video stream captured by a video camera, the characteristics of the video stream may be adapted to the new requirements.
According to embodiments, the set of characteristics comprises at least some of the following characteristics: intended use, detected level of motion, image resolution, value of images’ Peak Signal to Noise Ratio, maximum processing cost.
For example, the intended use is viewing, recording and/or processing the first video stream.
For illustration purposes, when a mosaic of video streams captured by several cameras is displayed on a display device, the resolution of each video stream is preferably adapted to the size of the window displaying it.
This is because a video processing device may have limited processing resources preventing the processing of high quality video streams. By taking into account the maximum processing cost allowed by the device, the transmission of a video stream that cannot be processed is avoided. Also the adaptation of the resolution of the video stream to the size of the window for display may allow network bandwidth savings.
According to embodiments, the selecting step comprises:
determining video stream configurations that are compatible with the characteristics required for the first video stream; and selecting a video stream configuration compatible with a number of streams that the video camera can generate based on the source flow.
According to embodiments, the selecting step further comprises: classifying the video stream configurations determined as compatible, according to their distance from the required characteristics; and selecting, among the classified video stream configurations, the video stream configuration having the closest characteristics to the required characteristics.
Advantageously, thanks to the classifying step, the selection of a given configuration will be facilitated.
According to embodiments, the method comprises a step of modifying a current video stream configuration of the second video stream into the selected video stream configuration for the second device.
According to embodiments, the first video stream is of higher quality than the second video stream, and the step of modifying comprises selecting characteristics increasing the quality of the second video stream with respect to its current quality.
According to embodiments, the resource constraints of the video surveillance system include at least one of the following parameters: maximum number of video streams that can be transmitted, processing capability of devices involved in the processing of the first video stream, memory storage capacity, network bandwidth. Typically, the maximum number of video streams that can be transmitted may be equal to two or three.
According to embodiments, the method comprises a step of notifying the first device of a current video stream configuration of the second video stream to the second device.
For instance, the first device may be notified of the second video stream being currently received by the second device in high resolution so that if the first device operator does not mind, it can accept receiving the (first) video stream based on the same source flow in low resolution only.
According to embodiments, the method comprises a step of notifying the second device of the request from the first device.
For example, the second device currently receiving the second video stream may be notified about the first device wishes of using the same source flow (i.e. notified about the request concerning the first video stream), so that if the second device operator does not mind, it can decide to stop using the source flow, i.e. to agree on terminating the transmission of the second video stream.
According to embodiments, several possible video stream configurations are selected for at least one of the first device and the second device and the method comprises a step of notifying the first device and/or the second device about the selected possible video stream configurations.
For instance, the video stream configurations may comprise different display layouts that are all compatible with the characteristics requested by the device. Then, the operator of the device may validate one of the proposed display layouts.
Correspondingly, according to a second aspect of the present invention, there is provided a device for managing video streams in a video surveillance system comprising a plurality of devices, the managing device being configured for:
receiving a request from a first device of the video surveillance system, the request concerning a first video stream which is based on a source flow generated by a video camera, a second device of the video surveillance system receiving a second video stream which is based on said source flow;
selecting a video stream configuration for at least one of the first device and the second device, said selecting being based on the request, on the current use of said source flow generated by the video camera and on resource constraints of the video surveillance system.
According to a third aspect of the present invention, there is provided a video surveillance system comprising a plurality of devices and a managing device as aforementioned.
According to embodiments, said devices are display devices, recording devices, and/or processing devices.
The display device may be called « viewer » in the following description. For instance, the recording device is a recording server.
The processing device may be configured to run Video Content Analytics (VCA) algorithms, for instance for face detection or recognition, people tracking, or license plate reading.
The device and system according to the second and third aspects have similar advantages and features as the method aforementioned.
The invention also concerns a method substantially as described herein with reference to Figures 4, 5 and 6 of the accompanying drawings, a device substantially as described herein with reference to Figures 1, 2 and 3 of the accompanying drawings, and a video surveillance system substantially as described herein with reference to Figure 2 of the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the invention will now be described, by way of example only, and with reference to the following drawings in which:
Figure 1 comprises Figures 1a, 1b and 1c illustrating exemplary video streams exchanged in a video surveillance system according to embodiments;
Figure 2 illustrates an exemplary architecture of a video surveillance system according to embodiments;
Figure 3 illustrates a possible architecture for a device according to embodiments;
- Figure 4 illustrates steps of a method according to embodiments;
Figure 5 illustrates steps for determining video stream configurations that are compatible with the requirements of the first device;
Figure 6 illustrates steps for selecting a video stream configuration for each device using the same source flow; and
Figure 7 comprises Figures 7a and 7b respectively illustrating the display screen of the second device of the system of Figure 2 and a new possible display layout for this second device after execution of the algorithm of Figure 5.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
The invention is now described by means of specific non-limiting exemplary embodiments and by reference to the drawings.
Figure 1 illustrates exemplary video streams exchanged in a video surveillance system according to embodiments.
In the given example, a video surveillance system comprises several devices 100, 120 and 150 able to generate and/or process video streams based on a source flow. In particular, Figure 1a shows a video camera 100, Figure 1b shows a recording server 120 and Figure 1c shows a VCA server or display device 150 (also called “viewer”). The present invention is not limited to these exemplary devices and a video surveillance system according to the present invention may also comprise other devices.
In Figure 1a, the surveillance video camera 100 is configured to capture a source flow consisting of raw video data representing a given scene 105. The source flow may be processed by a set of independent video encoders 110, 111 and 112 embedded in the video camera 100. Each video encoder is set up according to encoding parameters such as an encoding algorithm (typically H264 or MJPEG), a frame rate, a resolution, and a compression rate. The video encoders are configured to process the source flow and to generate “video streams” as output data, using encoding parameters that will be described below.
The set-up of an encoder depends on the characteristics of the source flow (i.e. of the input of the encoder) and on the characteristics wished for the video stream (i.e. for the output of the encoder).
Thanks to the use of multiple encoders, independent video streams with different characteristics can be generated simultaneously from the same source flow captured by the video camera 100.
For instance, the encoder 110 is configured to generate the video stream 120, the video encoder 111 is configured to generate the video stream 121 and the encoder 112 is configured to generate the video stream 122. In this example, the video camera 100 is configured to generate up to 3 different video streams simultaneously.
The three video streams 120, 121 and 122 output from the video camera 100 may have different characteristics. The characteristics associated with a video stream define a video stream configuration. Each video stream output by a video camera 100 may be destined for a predetermined device, module or application of the video surveillance system, for instance a recording server, a VCA server or a display device.
In Figure 1b, the recording server 120 is configured to receive and store input video streams 140 and 141 based on the source flows captured by different video cameras. The recording server 120 may also comprise a module 125 configured to process a received (input) video stream (e.g. 140) having first characteristics to generate a (modified) output video stream (e.g. 142) having second characteristics. The module 125 may perform different operations such as transcoding, reduction of frame rate, reduction of resolution, and modification of the compression rate. These operations may be combined. For instance, a second video stream having a resolution of 720p and a frame rate of 10 frames per second (fps) may be generated from a first video stream having a resolution of 1080p and a frame rate of 30 fps. In practice, each operation has its own processing cost which depends on the type of the operation, the first characteristics of the input video stream 140 and the second characteristics of the output video stream 142. In practice, the number of video streams at the input and at the output of the recording server 120 is limited. It depends on the processing power and on the storage capacity of the recording server 120.
In Figure 1c, the VCA server or display device 150 receives an input video stream 160 based on the source flow captured by a video camera (e.g. 100) or a recording server (e.g. 120). The VCA server or display device 150 is configured to decode the received video stream in order to re-generate the source flow that may have been encoded for transmission. The VCA server is also configured to analyze the images while the display device 150 is configured to display the images.
In the following description, it is assumed that only the video cameras generate video streams. However, the invention is not limited thereto and as mentioned previously, a recording server may also generate video streams. In both cases, the resource constraint relating to the number of video streams that can be simultaneously generated must take into account the video streams output by the video camera and the recording server(s) if there is any.
Figure 2 illustrates an exemplary architecture of a video surveillance system 200 according to embodiments.
In the given example, the video surveillance system 200 comprises three remote sites 210, 220, 230, one central site (also called headquarters) 240 and a backbone network 205 which interconnects the remote sites and the central site.
The first remote site 210 comprises a set of two video cameras 211 and 212 similar to the video camera 100 described with reference to Figure 1a. These video cameras are interconnected by a dedicated infrastructure network 215.
The second remote site 220 comprises a video camera 223 similar to the video camera 100 described with reference to Figure 1a and a recording server 222 similar to the recording server 120 described with reference to Figure 1b, typically configured to store the video stream based on the source flow captured by the video camera 223. They are both interconnected by a dedicated infrastructure network 225.
The third remote site 230 comprises two display devices 231 and 232 similar to the display device 150 described with reference to Figure 1c, both interconnected by a dedicated infrastructure network 235.
For illustration purposes, the display device 231 displays images 236 having a high resolution (e.g. zoom of a particular region of interest) based on the source flow captured by the video camera 212 while the display device 232 displays images 237 having a medium resolution based on the source flow captured by the video camera 212 and also images 238 having a medium resolution based on the source flow captured by the video camera 223.
The central site 240 comprises the following devices that are interconnected by a dedicated infrastructure network 245:
- a display device 241 configured to display received video streams, similar to the display device 150 described with reference to Figure 1c,
- a set of recording servers 242 configured to store received video streams, similar to the recording server 120 described with reference to Figure 1b,
- a set of Video Content Analytics (VCA) servers 243 configured to analyse the received video streams, similar to the VCA server 150 described with reference to Figure 1c, and
- a Video Manager System (VMS) 244 configured to manage the video surveillance system.
The display device 241 may display a composite image comprising low resolution images 251, 252 and 253 based on the source flows captured by the video cameras 211,212, 223 respectively.
The set of recording servers 242 may be configured to store video streams that are not already stored in a remote site. For instance, the first remote site 210 does not comprise a recording server and consequently, the set of recording servers 242 may be used to record video streams based on the source flows captured by the set of video cameras 211 and 212. In other words, video streams may be stored locally or remotely from the video camera capturing the source flow based on which the video streams are computed.
The Video Manager System 244 comprises a software module configured to set-up, control and manage the video surveillance system 200. It may comprise an administration interface through which the devices and modules of the video surveillance system may be set up. The Video Manager System 244 may thus implement embodiments of the invention and manage the configuration of all video streams.
In practice, any request concerning a video stream, for instance for obtaining a video stream having specific characteristics (requirements) or modifying an existing video stream (e.g. because of a change of use) is transmitted by the requesting device to the Video Manager System 244.
For instance, such a request may imply:
- the creation of a new video stream, e.g. a display device requests a new video stream in order to display new images based on a source flow captured by a video camera and not currently displayed,
- the modification of an existing video stream i.e. of its characteristics, e.g. a display device requests to modify the characteristics of the video stream currently received (for instance, digital zoom on a region of interest requiring the image resolution to be increased),
- the termination of an existing video stream, e.g. a display device requests to stop receiving images from a given video camera.
The different sets of characteristics (configurations) that can be used to generate a video stream to be transmitted based on a source flow captured by a given video camera may be defined by the administrator at the installation of said video camera. In a variant, they may also be automatically defined by the VMS 244 based on an analysis ofthe requirements ofthe intended use (e.g. display, analysis, processing).
For illustration purposes, the resolution of a video stream for a display device can be equal to the resolution of the screen, the frame rate can be equal to 15fps by default, and the compression ratio can be selected by estimating the Peak Signal to Noise Ratio (PSNR) at the output of the encoder. For instance, the compression ratio is progressively decreased up to obtain a predefined target PSNR of 30.
An aim of embodiments of the present invention is to allocate an appropriate configuration (from among the defined configurations) to each device of the video surveillance system wishing to use the source flow captured by a given video camera, taking into account the resource constraints (e.g. processing load, storage memory consumption, network bandwidth consumption) ofthe overall system.
For illustrative purposes, when several video streams are concurrently transmitted over the network 205, for instance a first video stream from the video camera 212 is transmitted to the display device 231 and a second video stream from the video camera 223 is transmitted to the display device 241, the links 261 and 263 must both support the throughput generated by the first video stream and the links 262 and 264 must both support the throughput generated by the second video stream. However, the link 260 between the network switches (not shown) that are used to route the network data through the network 205 to the correct destination must support the sum of the throughput generated by the first video stream plus the throughput generated by the second video stream.
According to embodiments of the present invention, the overall bandwidth is dynamically taken into account for defining the appropriate video stream configurations for all the devices implicated in the use of source flows generated in the video surveillance system.
The VMS 244 is also configured to transmit to each video camera of the system the list of configurations it has to use for generating the video streams based on its source flow.
The dedicated infrastructure networks 215, 225, 235 and 245 are typically Local Area Networks (LAN) based on hierarchical architecture with 10/100/1000 Mbps Gigabit Ethernet, RJ-45 using Ethernet switches.
The network deployment of the video surveillance system shown in Figure 2 is a non-limiting example and the present invention is not limited thereto. For example, in embodiments, some VCA servers 243 may be installed in remote sites.
Figure 3 illustrates a possible architecture for a device 300 according to embodiments, for instance the Video Manager System 244 shown in Figure 2.
In this exemplary architecture, the device 300 comprises a communication bus 305 to which there are connected:
- a micro-controller or Control Process Unit (denoted CPU) 310;
- an Input/Output (I/O) interface module 320 configured to input parameters to be used in a method according to embodiments; it may be used by an administrator of the video surveillance system to configure the VMS 244;
- a Read-Only Memory (denoted ROM) 330 in which instructions for implementing steps of a method according to embodiments may be stored;
- a Hard Disk (denoted HD) 340;
- a Random Access Memory (denoted RAM) 350, working as a main memory, in which instructions and temporary variables and parameters for implementing steps of a method according to some embodiments may be loaded from a non-volatile memory, and whose capacity may be extended by an additional Random Access Memory connected to an expansion port (not shown);
- a network interface module 360 enabling connections with other devices (video cameras, recording servers, VCA servers) through the communication network 205. Digital data to be processed are typically transmitted or received through this interface.
The communication bus 305 provides communication and interoperability between the various elements included in the device 300 or connected to it. For instance, the CPU 310, the ROM 330, the HD 340, the RAM 350, and the interfaces 320, 360 exchange data and control information via the communication bus 305. The representation of the bus is not limiting and in particular the CPU 310 is operable to communicate instructions to any element of the device 300 directly or by means of another element of the device 300.
After the communication device 300 has been powered on, the CPU 310 is capable of executing, from the RAM 350, instructions pertaining to a computer program, once these instructions have been loaded from the ROM 330, the HD 340 or from an external memory (not shown in Figure 3). The computer program causes the CPU 310 to perform some or all of the steps of the algorithms described with reference to Figures 4 to 6.
Figure 4 illustrates steps of a method according to embodiments. These steps may be performed by the Video Manager System 244 shown in Figure 2 or in a variant, by other device(s) able to communicate with the Video Manager System 244.
Embodiments of the present invention deal with contexts in which several uses are concurrently active for the same video camera, i.e. several devices of the video surveillance system receive video streams based on the same source flow captured by the same video camera, these video streams having different characteristics.
There is provided a method for managing video streams and comprising:
- receiving a request from a first device of the video surveillance system, the request concerning a first video stream which is based on a source flow generated by a video camera, a second device of the video surveillance system receiving a second video stream which is based on the same source flow;
- selecting a video stream configuration for at least one of the first device and the second device, said selecting being based on the request, on the current use of said source flow generated by the video camera and on resource constraints of the video surveillance system.
Thus, the requesting device receives the (requested) first video stream which is adapted to its requirements but also which takes into account the system resources constraints and the other video streams currently transmitted that are based on the same source flow captured by the same video camera. Preferably, the video stream configurations of the video streams currently transmitted are also adapted depending on the system resources constraints.
Advantageously, available resources for data processing, storage, and network bandwidth are saved.
The algorithm is triggered upon reception (step 400) of a request from a device, for instance one of the devices 222, 231, 232, 241, 242, 243 or 244 shown in Figure 2, here referred to as the requesting device. This request concerns a first video stream which is based on a source flow generated by a video camera of the system, for instance the video camera 211, 212 or 223 shown in Figure 2. For instance, the request is received through the communication interface 360 shown in Figure 3.
At step 401, the received request is processed. In particular, its kind (add, modify or stop) is identified. This is because the request may be either for receiving the first video stream as a new video stream or for modifying the first video stream currently received or for terminating the transmission of the first video stream currently received (termination request). For instance, the aim of the request may be indicated by a dedicated flag or by a specific header in the request.
Unless it is for terminating an existing first video stream, the request may indicate a set of characteristics (requirements) required for the first video stream. This is because, as mentioned previously, a video stream is an encoded version of a source flow captured by a given video camera and the encoding parameters depend notably on the required characteristics. These characteristics are retrieved from the request at step 401 and may for instance comprise:
- the type of intended use (display, recording, VCA),
- the type of captured scene (e.g. the level of motion detected),
- a targeted image resolution,
- a targeted PSNR (Peak Signal to Noise Ratio) of images,
- a maximum processing cost (targeted processing load to process the video stream).
This last characteristic may be useful because the requesting device may have limited processing resources, for example preventing the processing of high quality video stream.
At step 402, it is checked whether the request is a termination request, i.e. a request for terminating the transmission of a video stream currently received.
If this is not the case, i.e. if a new video stream is requested or if modification of a video stream currently received is requested, one or more configurations compatible with the requirements of the requesting device is/are selected from a list of available configurations (step 404). As mentioned previously, a set of possible configurations have been predefined for the video camera (e.g. default video stream configurations) either by the administrator, or automatically by the VMS 244. This set of configurations may be modified or enriched by the VMS 244 during operation of the system. A possible implementation of this step is described hereafter with reference to Figure 5.
Next, at step 406, it is checked whether the source flow on which is based the first video stream targeted in the request is already used by a device (or several devices) of the system, i.e. whether a device of the system is currently receiving a second video stream based on the same source flow captured by the same video camera.
This device may be the requesting device itself, typically if the request is for modifying the first video stream, or it may be another device (or several others) of the system called remote device(s), typically if the request is for adding a new first video stream.
If the first video stream is not already in use, the configuration which is the closest to the requirements of the requesting device is selected (step 409) from among those selected at step 404. This selection takes into account the constraints of the system in terms of resources consumption.
For instance, these constraints may include:
- the current processing load in (and processing capacity of) the requesting device, as an indicator of whether or not the requesting device will be able to process (to decode, to display or to analyse) a video stream with given characteristics,
- the amount of memory available for storage in the requesting device, in the case of a recording server,
- the load of the network (e.g. available bandwidth) which is useful for estimating whether the infrastructure will be able to support the transmission of a video stream with given characteristics. It concerns the maximum bandwidth supported by the network links 260, 261,262, 263 and 264 as exemplified with reference to Figure 2.
In practice, according to a possible implementation, the available resources of the video surveillance system may be monitored using two lists h and l2 as explained hereinafter.
The first list h corresponds to the available network resources on each communication link 260, 261, 262, 263 and 264 of the video surveillance system. The size of the first list h is the number of communication links in the video surveillance system (here 5). According to an exemplary embodiment, each ith element of the list h corresponds to the ith communication link of the video surveillance system. The ith element is equal to the network capacity (i.e. total supported bandwidth) of the ith link of the video surveillance system minus the sum of the resources (throughput) currently consumed by the set of video streams involving the ith link.
The second list l2 corresponds to the available processing resources of each device able to generate and process video streams. The size of the list l2 is the number of devices able to generate and process video streams in the video surveillance system. Each jth element of l2 corresponds to the jth device of the video surveillance system (able to generate and process video streams). It is equal to the processing capacity (storage memory and/or processing power) of the jth device of the video surveillance minus the sum of the resources consumed by the set of video streams already involving the jth device.
The capacity of each resource (i.e. the initial value of each element of the lists h and l2) may be obtained by experimentation on the video surveillance system during an installation phase.
When the step 409 is implemented, the expected status of lists h and l2 after encoding and transmission of each possible video stream configuration is checked. If one of the elements of the lists h or l2 falls to zero, it means that the corresponding resource is saturated and the corresponding configuration is rejected.
In the case of a failure to select one configuration due to the resource constraints, the algorithm ends at step 410 after notifying the requesting device about the need to modify the requirements and then start the algorithm again.
Back to step 406, if the source flow is already used by a device (requesting device or other remote device(s)), a configuration is selected for each device using the source flow. As for the selection of step 409, the configuration selected for each device is the closest to the requirements of this device while taking into account the system constraints. A possible implementation of this step is described hereafter with reference to Figure 6. As a possible consequence, the current configuration used by a given device may be modified to better match the new system resource constraints/occupancy.
Next, the algorithm ends at step 410 already described.
Back to step 402, if the received request is a termination request, i.e. a request for terminating the transmission of a video stream currently received by the requesting device, then at step 403, a command is sent to the video camera transmitting the video stream in order to stop the transmission of this video stream to the requesting device.
At step 405, it is checked whether the source flow on which is based the first video stream targeted in the request is already in use by another device (or several other devices) of the system, i.e. whether another device (called remote device) of the system is currently receiving a second video stream based on the same source flow captured by the same video camera. More specifically, it is first determined whether the first video stream targeted in the request is also being transmitted (e.g. broadcast) to another device of the system, because, in this case, the first video stream must not be terminated for all devices. It is then determined whether a second video stream (different from the first video stream) based on the source flow is currently being transmitted to another device (similarly to the test performed at step 406).
If the source flow is not used by any other device, the algorithm ends at step 407 by stopping the generation of the video stream which is no longer utilized by any device.
If the source flow is used by another device, the step 408 (already described) is performed in order to review the allocation of configurations to all the devices utilizing the source flow. It should be noted that in the case where another device is receiving the first video stream (broadcast), the configuration used for this transmission may also be modified.
Figure 5 illustrates steps for determining video stream configurations that are compatible with the requirements of the first device (requesting device) during step 404 shown in Figure 4. These steps may be performed by the Video Manager System 244 shown in Figure 2 or in a variant, in other device(s) able to communicate with the Video Manager System 244.
At step 501, the minimum values of encoding parameters (including image parameters) that fulfil the requirements indicated in the request (and retrieved at step 401) are determined. As mentioned previously, these requirements may include for instance:
- the type of intended use (display, recording, VCA),
- the type of captured scene (e.g. the level of motion detected),
- a targeted image resolution,
- a targeted PSNR (Peak Signal to Noise Ratio) of images,
- a maximum processing cost (targeted processing load to process the video stream).
In the present description, the terms “encoding parameters” refer to the parameters that will be applied to the source flow to generate a video stream with characteristics compatible with the requirements. Thus, two video streams issued from the same source flow differ only by the encoding parameters used for generating them based on the source flow.
For instance, the encoding parameters may be:
- the type of encoding (e.g., MPEG, H264),
- the compression level (or coding rate),
- the profile (e.g. baseline, main, high, etc.),
- the group of picture (GOP) compression rate in the case of H264 encoding,
- the image resolution (number of pixels per image),
- the frame rate (number of frames per second of video).
For illustration purposes, if a user wishes to display the video stream with a resolution of 1280x720 pixels, then the image resolution of the video stream to generate must be at least 1280x720 pixels. A full HD (high Definition) video stream is also acceptable as it provides even more pixels (1920x1080).
In another example, if the first device (requesting device) is a display device, the encoding quality (i.e. compression ratio) is preferably chosen so as to obtain a targeted PSNR for the decoded images. Also, the frame rate is preferably chosen so as to get a smooth display of motion. However, if the first device (requesting device) is a VCA in charge of license plate or face detection and recognition, the frame rate can be low.
According to embodiments, the determination of the minimum values of encoding parameters may also take into account the current use of the source flow captured by the video camera, by other devices of the system, i.e. whether the source flow is already recorded, displayed or analysed by another device.
At step 502, a list of configurations predefined at the installation of the system for the video camera is retrieved from memory (e.g. 340 or 360 shown in Figure 3). As mentioned previously, this list of configurations may be composed of default configurations set either by an administrator or automatically by the VMS 244.
At step 503, at least one configuration is selected from the list of configurations. In practice, only the configurations of the list that are compatible with the minimum values of encoding parameters determined at step 501 may be selected. For example, all of them (i.e. all available compatible configurations) are selected.
It may happen that none of the configurations matches one of the minimum values (for instance a frame rate of 30 fps). In this case, if the video camera is able to generate a video stream with the minimum values of the encoding parameters, a new configuration is generated based on these minimum values and added in the list retrieved at step 502. In this way, the list is enriched.
If several configurations are selected, these configurations are classified at step 504. For instance, they are classified from the configuration the closest to the requirements to the configuration the farthest from them.
For illustration purposes, if a user wishes to display the video stream with a resolution of 1280x720 pixels (requirements), configurations with 1280x720 pixels and 1920x1080 pixels are both compatible. The configuration with 1280x720 pixels will be classified first and the configuration with 1920x1080 pixels will be classified second since it is less close to the requirements.
Advantageously, the selection of a given configuration in steps 409 and 408 will be facilitated.
Figure 6 illustrates steps for selecting a video stream configuration for each device using the same source flow during step 408 shown in Figure 4. These steps may be performed by the Video Manager System 244 shown in Figure 2 or in a variant, in other device(s) able to communicate with the Video Manager System 244.
At step 601, a list of configurations is retrieved for each video camera from memory (e.g. 340 or 360 shown in Figure 3). As mentioned previously, this list of configurations may be composed of default configurations set either by an administrator or automatically by the VMS 244 as well as configurations added in the list during operation of the system as described with reference to step 503 shown in Figure 5.
At step 602, possible allocations (preferably all) of configurations for all devices receiving or wishing to receive the same source flow are computed. An example of output of this step for the system shown in Figure 2 is illustrated in the following table:
Display device 231 configuration Display device 232 configuration Display device 241 configuration Recording device 242 configuration VCA 243 configuration
High Medium Low High High
High Medium Medium High High
High High Low High High
High High High High High
In this example, it is assumed that all of the devices 231, 232, 241, 242 and 243 use the source flow captured by the same video camera 212 that is assumed to be capable of generating up to two video streams concurrently. In this illustrative example, there are only three possible configurations providing respectively a high quality video stream (“high”), a medium quality video stream (“medium”) and a low quality video stream (“low”). Obviously, embodiments ofthe present invention are not limited thereto.
Each row of this table corresponds to a given allocation of the configurations for the devices and each column corresponds to the possible configurations that are compatible with the requirements of a given device.
In this example, it is assumed that the display device 231 has required the video stream to be suitable for display on a HD screen and thus can only accept the high quality video stream (i.e. configuration “high”).
It is also assumed that the display device 232 is the requesting device and requires the medium quality video stream as a new video stream (it does not use the source flow yet). It can accept both medium and high quality video streams (i.e. both configurations “medium” and “high” are compatible).
It is assumed that the display device 241 has required the video stream to be suitable for display on a low-resolution screen so it can accept low, medium and high quality video streams (i.e. configurations “low”, “medium” and “high” are compatible).
It is also assumed that the recording device 242 and the VCA 243 have 10 both required the high quality video stream (i.e. configuration “high”).
Therefore, the second row corresponds to the virtual situation where both display devices 231 and 232 receive the medium quality video stream.
At step 603, a number of concurrent video streams that must be generated for each possible allocation (i.e. for each row) is computed as well as a parameter called “network penalty”. The network penalty is an indicator of the consumption of network bandwidth. For instance, a different weight can be attributed to each configuration:
-1 point for the low quality video stream,
- 2 points for the medium quality video stream, and
- 4 points for the high quality video stream.
The computed sum of weights for each possible allocation (i.e. for each row) is stored in the last column as the network penalty for this allocation. The result may be modulated depending on the possibility to multicast the same video stream to several devices.
The result of the computing of step 603 is shown in the following table:
Display device 231 configuration Display device 232 configuration Display device 241 configuration Recording device 242 configuration VCA 243 configuration Number of video streams generated Network Penalty
High Medium Low High High 3 15
High Medium Medium High High 2 16
High High Low High High 2 17
High High High High High 1 20
In this example, the first allocation (first row) is such that three different qualities of stream (high, medium and low) are requested, thus three video streams should be generated by the video camera. The high quality stream must be duplicated to be provided to three devices (here the display devices 231, 242 and 243) with a network penalty of 4 points for each duplicated stream. The medium quality stream for the device 232 has a network penalty of 2 points and the low quality stream for the device 241 has a network penalty of 1 point. The total network penalty for the first allocation is thus 4*3 + 2 + 1 = 15. The same reasoning may be made for the other allocations.
In a variant of this example (not shown), the streams of different quality may be broadcast so that devices requiring the same quality of stream (as devices 231, 242 and 243) share the same quality video stream without duplication. In this variant, the resulting network penalty would be 7: 1 point for the low quality video stream plus 2 points for the medium quality video stream plus 4 points for the shared high quality video stream.
This table may be completed with other columns for other metrics such as the memory storage capacity required by each possible allocation and the processing load to analyse video stream in a VCA.
At step 604, the allocations exceeding the resources of the system are discarded. Typically, the allocations for which the number of video streams exceeds the maximum number of video streams that can be generated by the video camera are discarded. In the above example, the maximum number of video stream that can be concurrently generated by the video camera 212 is two. Consequently, the first allocation (first row) is discarded. The processing capabilities and memory resources of the devices may also be taken into consideration. For these purposes, the processing load required to generate the concurrent video streams may be estimated. As for the network bandwidth, a parameter called “processing penalty” may be computed with the following rules:
-1 point for the low quality video stream,
- 2 points for the medium quality video stream, and
- 4 points for the high quality video stream.
Finally, at step 605, the allocation having the lowest network penalty (last column) is selected.
If there are several possible choices, other metrics could be used to for the selection such as the processing load in the various devices of the system.
In a variant, one of the devices, for instance the requesting device, may be notified about the several configurations possible for it due to the several possible allocations. Typically, these configurations may correspond to different display layouts that are all compatible with the characteristics requested by the device. Then, the operator of the device may validate one of the proposed display layouts and thus the corresponding allocation is selected. This variant can be advantageous when the operator does not define specific requirements and lets the system propose several possible configurations.
The status of system resources can also be checked as for the step 409. By doing so, a configuration may be rejected if one of the system resources cannot support this additional video stream.
In the example above, the allocation corresponding to the second row in which the display device 232 receives the medium quality video stream is selected. As a consequence, the display device 241 is no longer receiving the low quality video stream but instead the medium quality video stream.
The display device 232 can thus receive the required medium quality video stream instead of being obliged to receive one of the existing video streams (i.e. either the low quality video stream which does not fulfil the requirement of the display device 232 or the high quality video stream which leads to waste processing load and network bandwidth).
In a variant, the requesting device (in the above example, the display device 232) may be notified about the current configuration of a video stream currently received by another device so that an operator of the requesting device may change its requirements or merely benefit from the existing video stream currently transmitted to the other device.
Figure 7 comprises Figures 7a and 7b respectively illustrating the display screen of the second device (e.g. the display device 241) of the system of Figure 2 and a new possible display layout for this second device after execution of the algorithm of Figure 5.
Taking the example of Figure 6, the display device 241 displays a composite image requiring low resolution images 251, 252, 253 based on the source flows captured by the video cameras 211, 212 and 223 respectively.
After execution of the algorithm of Figure 5, the display device 241 receives a medium quality video stream from the video camera 212, the display device 241 may thus display a medium resolution image 700 instead of the low resolution image 252.
This new layout is illustrated in Figure 7b. Other layouts of the composite images are also possible. They can be notified to the operator of the display device 241 who can accept or refuse the proposed layout.
Optionally, the requesting device (in the above example, the display device 232) may be notified about a current configuration of another video stream received by another device so that an operator of the requesting device may change its requirements or merely benefit from the existing video stream currently transmitted to the other device.
Optionally, the second device (e.g. display device 241) may be notified about the request from the first device (in the above example, the display device 232) so that an operator of the second device may change its requirements so as to free resources for the first device. For example, the second device currently receiving the second video stream may be notified about the first device's wishes to use the same source flow (i.e. notified about the request concerning the first video stream), so that if the second device operator does not mind, it can decide to stop using the source flow,
i.e. to agree on terminating the transmission of the second video stream.
Although the present invention has been described hereinabove with reference to specific embodiments, the present invention is not limited to the specific embodiments, and modifications which lie within the scope of the present invention will be apparent to a person skilled in the art. Many further modifications and variations will suggest themselves to those versed in the art upon making reference to the foregoing illustrative embodiments, which are given by way of example only and which are not intended to limit the scope of the invention as determined by the appended claims. In particular different features from different embodiments may be interchanged, where appropriate.

Claims (15)

1. A method for managing video streams in a video surveillance system comprising a plurality of devices, the method comprising:
receiving a request from a first device of the video surveillance system, the request concerning a first video stream which is based on a source flow generated by a video camera, a second device of the video surveillance system receiving a second video stream which is based on said source flow;
selecting a video stream configuration for at least one of the first device and the second device, said selecting being based on the request, on the current use of said source flow generated by the video camera and on resource constraints of the video surveillance system.
2. A method according to claim 1, wherein the request is for receiving the first video stream, for modifying the first video stream or for terminating the transmission of the first video stream.
3. A method according to claim 1 or 2, wherein the request indicates a set of characteristics required for the first video stream.
4. A method according to claim 3, wherein the set of characteristics comprises at least some of the following characteristics: intended use, detected level of motion, image resolution, value of images’ Peak Signal to Noise Ratio, maximum processing cost.
5. A method according to claim 3 or 4, wherein the selecting step comprises:
determining video stream configurations that are compatible with the characteristics required for the first video stream; and selecting a video stream configuration compatible with a number of streams that the video camera can generate based on the source flow.
6. A method according to claim 5, wherein the selecting step further comprises:
classifying the video stream configurations determined as compatible, according to their distance from the required characteristics; and selecting, among the classified video stream configurations, the video stream configuration having the closest characteristics to the required characteristics.
7. A method according to any one of the preceding claims, comprising a step of modifying a current video stream configuration of the second video stream into the selected video stream configuration for the second device.
8. A method according to claim 7, wherein the first video stream is of higher quality than the second video stream, and wherein the step of modifying comprises selecting characteristics increasing the quality of the second video stream with respect to its current quality.
9. A method according to any one of the preceding claims, wherein the resource constraints of the video surveillance system include at least one of the following parameters: maximum number of video streams that can be transmitted, processing capability of devices involved in the processing of the first video stream, memory storage capacity, network bandwidth.
10. A method according to any one of the preceding claims, comprising a step of notifying the first device of a current video stream configuration of the second video stream to the second device.
11. A method according to any one of the preceding claims, comprising a step of notifying the second device of the request from the first device.
12. A method according to any one of the preceding claims, wherein several possible video stream configurations are selected for at least one of the first device and the second device and the method comprises a step of notifying the first device and/or the second device about the selected possible video stream configurations.
13. A device for managing video streams in a video surveillance system comprising a plurality of devices, the managing device being configured for:
receiving a request from a first device of the video surveillance system, the request concerning a first video stream which is based on a source flow generated by a video camera, a second device of the video surveillance system receiving a second video stream which is based on said source flow;
selecting a video stream configuration for at least one of the first device and the second device, said selecting being based on the request, on the current use of said source flow generated by the video camera and on resource constraints of the video surveillance system.
14. A video surveillance system comprising a plurality of devices and a managing device according to claim 13.
15. A video surveillance system according to claim 14, wherein said devices are display 10 devices, recording devices, and/or processing devices.
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Application No: Claims searched:
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