CN104349163A - Measurement display device and measurement system for end-to-end video transmission delay - Google Patents
Measurement display device and measurement system for end-to-end video transmission delay Download PDFInfo
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- CN104349163A CN104349163A CN201410691825.2A CN201410691825A CN104349163A CN 104349163 A CN104349163 A CN 104349163A CN 201410691825 A CN201410691825 A CN 201410691825A CN 104349163 A CN104349163 A CN 104349163A
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Abstract
The invention discloses a measurement display device and a measurement system for an end-to-end video transmission delay. The device comprises a high-speed time stamp generator and at least two display controllers, wherein each display controller is connected with a display unit; the display units are in arrayed distribution to form a display array; the high-speed time stamp generator is used for acquiring synchronous time from a GPS (Global Positioning System) time service clock at a predetermined time interval to generate a time stamp and sending the time stamps generated in different periods of time to the display controllers in sequence; the display controllers are used for acquiring the time stamps which are sent from the high-speed time stamp generator so as to drive the display array; the display array is used for displaying the time stamps generated in different periods of time on each display unit in sequence respectively. According to the device and the system, the measurement accuracy of a time delay is improved, and the requirements on the time delay measurement accuracy of a video processing system which is highly sensitive to the time delay are met; meanwhile, measurement system equipment is simple, and the cost is greatly reduced.
Description
Technical field
The present invention relates to Video transmission system time delay measurement field, particularly a kind of end-to-end video transmission delay measurements display unit and measuring system.
Background technology
Time delay is the time order and function order between processing system for video constrained input.Each component units of processing system for video, as video acquisition, coding, transmission, decoding, display, and interface and buffer memory all can be delayed.Time delay is also called CDL (Capture-to-Display Latency) end to end, refers to the time difference experienced to receiving terminal display video picture from transmitting terminal collection video pictures.CDL is one of important indicator weighing Video transmission system service quality, the real-time of the quantitative system that characterizes.Measuring junction is more to looking closely related method thereof frequently, and researcher both domestic and external, professional equipment provide commercial city to give relevant solution.These schemes are mainly divided into two large classes, specific as follows:
The first kind is called intrusive mood method of measurement, cardinal principle is, the special video-audio signal that transmitting terminal customization produces, and sends into coding and transmission system, receive these signals by special measuring equipment at receiving terminal or the measurement point of specifying, computing time, difference was as the time delay between 2 o'clock.Adopt the normally professional equipment manufacturer of this kind of scheme, the module related measurement devices that such as Rohde & Schwarz Representative Office, Imtech etc. provide.Its advantage is that certainty of measurement is high, supports more tested point.Shortcoming needs specialty, expensive equipment, because relate to collection and the display of image, these professional equipments cannot substitute collection and the display device of user's use, therefore intrusive mood method is difficult to accurately measure time delay CDL end to end, particularly transmitting terminal and receiving terminal are not in the same localities, and belong to the situation in long-range strange land.
Equations of The Second Kind is called non-intrusion measurement method, its cardinal principle is, transmitting terminal embeds the symbol that can represent timestamp on video pictures, i.e. transmitting time stamp, when receiving terminal demonstrates the video pictures with transmitting time stamp, extract transmitting time stamp and compare with the local time stamp of receiving terminal, thus obtaining time delay CDL.Existing common methods is Presentation Time Stamp on the computer screen, and gather video pictures with video camera facing to computer screen, thus incorporate in video image by timestamp, the Video coding with timestamp compresses by transmitting terminal, and is transferred to receiving terminal.Receiving terminal is decoded and is demonstrated the video pictures with timestamp.The method of measurement of existing non-intrusive, timestamp has the additional character of digital form, bar code, Quick Response Code and design usually.Main purpose wishes to utilize existing, more stable, that reliability is high codeword generator and code reader.Although these class methods do not need expensive professional test equipment, the precision of the time delay measured be limited by the refresh rate of computer display, display video picture delay, the frame per second of video camera, the time for exposure, transmitting-receiving two-end clock synchronization accuracy impact thus make its certainty of measurement lower.These class methods are usually used in the low precision measure of video time delay of IP network, its certainty of measurement cannot meet the measurement requirement to the extremely sensitive processing system for video of time delay, such as terrestrial DTV, unmanned plane real time reconnaissance, infrared imaging guidance weapon, telesurgery systems etc.
Summary of the invention
The object of the invention is to overcome above-mentioned deficiency existing in prior art, a kind of end-to-end video transmission delay measurements display unit and measuring system are provided, to meet the latency measurement required precision to the extremely sensitive processing system for video of time delay, reduce costs.
In order to realize foregoing invention object, the technical solution used in the present invention is: a kind of end-to-end video transmission delay measurements display unit, comprise timestamp high-speed generator, described timestamp high-speed generator connects at least two display controllers, described at least two display controllers connect a display unit separately respectively, and described array of display cells arrangement forms array of display;
Described timestamp high-speed generator, for producing a timestamp lock in time every the scheduled time from the acquisition of GPS time service clock, sends the described timestamp of different time generation successively to described at least two display controllers; The wherein said scheduled time is Millisecond;
Described at least two display controllers, for obtaining the timestamp that sends from described timestamp high-speed generator thus driving described array of display;
Shown array of display, for showing the described timestamp of different time generation successively respectively at each display unit.
Preferably, at least two display controllers described in described timestamp high-speed generator is connected by bus, described at least two display controllers have unique bus address separately;
Described timestamp high-speed generator is specifically for producing a timestamp lock in time every the scheduled time from the acquisition of GPS time service clock, each described timestamp is generated the bus data frame with described bus address, sends described bus data frame successively to described bus;
Described at least two display controllers, specifically for obtaining the corresponding described bus data frame that from described timestamp high-speed generator send unique with respective described bus address according to respective described bus address from described bus respectively, are resolved described bus data frame and are extracted timestamp wherein thus drive described array of display;
Shown array of display, for showing the described timestamp of different time generation successively respectively at each display unit.
Preferably, if any one the display controller second time in described at least two display controllers receives the described bus data frame corresponding with its unique described bus address that described timestamp high-speed generator sends, then show the timestamp corresponding with current described bus data frame with the display unit that any one display controller described connects in described array of display, otherwise the described timestamp before display all the time.
Preferably, in described array of display, each display unit shows the described timestamp of different time generation respectively according to described display unit priority distributing order from left to right, from top to bottom.
Preferably, each display unit in described array of display is LCD display unit, and multiple LCD display unit forms LCD array of display according to ranks alignment.
The present invention also provides a kind of end-to-end video transmission delay measurements system, comprising:
First measures display unit, namely above-mentioned end-to-end video transmission delay measurements display unit, for generating at transmitting terminal and show the timestamp of different time generation according to array way on described array of display;
First video acquisition unit, for gathering the timestamp image frame that described first measures the different time generation that the array of display of display unit shows, is sent to video delivery network by described image frame compression coding generating video stream;
Described video delivery network, is connected with described first video acquisition unit, for transmitting described video flowing;
Video display unit, is connected with described video delivery network, for receiving described video flowing, decoding and show decoded image frame to described video flowing;
Second measures display unit, and to measure display unit identical with described first, and start with described first measurement mechanism simultaneously, for generate at receiving terminal and according to the timestamp of array way display different time generation on described array of display;
Second video acquisition unit, records for gathering simultaneously the video information that described second measures the timestamp image frame of the different time generation that the array of display of display unit shows and the decoded image frame of described video display unit display;
Analytic unit, the described second described video information measuring display unit and described video display unit for collecting described second video acquisition unit is decoded, each frame is saved as piece image, then in the picture described second measure the maximum very first time stamp of display unit extracted region, the second timestamp that described video display unit extracted region is maximum in the picture, the difference calculating stamp of the described very first time and the second timestamp is time delay measurement value.
Preferably, described second video acquisition unit collection recorded for the described second time of measuring the image frame video of display unit and described video display unit is 3-5 minute.
Preferably, described analytic unit, also for calculating described time delay measurement value respectively to every two field picture, gets the mean value of multiple described time delay measurement value as transmission system time delay measurement value end to end.
Preferably, the frequency acquisition of described first video acquisition unit is
f s, the refresh rate of described video display unit is
f d, the frequency acquisition of described second video acquisition unit is
f r, wherein,
f d>=
f r>=
f s.
Preferably, described first video acquisition unit and the second video acquisition unit are video camera, and described video display unit is LCD display.
compared with prior art, beneficial effect of the present invention: the present invention measures in display unit the array of display devising the display unit formation that can show multiple timestamp, at the timestamp that different position display is different, avoid at the quick Presentation Time Stamp in same position, surrounding time stamp is overlapping, thus define timestamp image clearly, improve the accuracy of time-stamp Recognition.Utilize that its measuring junction can generate more accurately to during end Video transmission system time delay, timestamp image more clearly, and then improve latency measurement precision, to meet the latency measurement required precision to the extremely sensitive processing system for video of time delay, measuring system equipment of the present invention is simple simultaneously, and cost reduces greatly.
accompanying drawing illustrates:
Fig. 1 is the end-to-end video transmission delay measurements display unit schematic diagram in the embodiment of the present invention;
Fig. 2 is LCD array schematic diagram in the embodiment of the present invention;
Fig. 3 is the end-to-end video transmission delay measurements system schematic in the embodiment of the present invention;
Fig. 4 is video sampling process and deviation schematic diagram;
Fig. 5 is the end-to-end video transmission delay measurements system transmitting terminal video acquisition process schematic in the embodiment of the present invention;
Fig. 6 is the end-to-end video transmission delay measurements system receiving terminal video acquisition process schematic in the embodiment of the present invention.
Embodiment
Below in conjunction with embodiment, the present invention is described in further detail.But this should be interpreted as that the scope of the above-mentioned theme of the present invention is only limitted to following embodiment, all technology realized based on content of the present invention all belong to scope of the present invention.
The present invention measures in display unit the array of display devising the display unit formation that can show multiple timestamp, at the timestamp that different position display is different, avoid at the quick Presentation Time Stamp in same position, surrounding time stamp is overlapping, thus form timestamp image clearly, improve the accuracy of time-stamp Recognition.
Utilize that its measuring junction can generate more accurately to during end Video transmission system time delay, timestamp image more clearly, and then improve latency measurement precision, to meet the latency measurement required precision to the extremely sensitive processing system for video of time delay, test macro equipment of the present invention is simple simultaneously, and cost reduces greatly.Illustrate below in conjunction with accompanying drawing.
End-to-end video transmission delay measurements display unit of the present invention, comprise timestamp high-speed generator, described timestamp high-speed generator connects at least two display controllers, described at least two display controllers connect a display unit separately respectively, and described array of display cells arrangement forms array of display.
Described timestamp high-speed generator, for producing a timestamp lock in time every the scheduled time from the acquisition of GPS time service clock, sends the described timestamp of different time generation successively to described at least two display controllers; The wherein said scheduled time is Millisecond, and those skilled in the art can be arranged as the case may be.
Described at least two display controllers, for obtaining the timestamp that sends from described timestamp high-speed generator thus driving described array of display.
Shown array of display, for showing the described timestamp of different time generation successively respectively at each display unit.
Concrete, referring to Fig. 1, at least two display controllers described in described timestamp high-speed generator is connected by bus, described at least two display controllers have unique bus address separately.Described timestamp high-speed generator is specifically for producing a timestamp lock in time every the scheduled time from the acquisition of GPS time service clock, each described timestamp is generated the bus data frame with described bus address, sends described bus data frame successively to described bus; Described at least two display controllers, specifically for obtaining the corresponding described bus data frame that from described timestamp high-speed generator send unique with respective described bus address according to respective described bus address from described bus respectively, are resolved described bus data frame and are extracted timestamp wherein thus drive described array of display; Shown array of display, for showing the described timestamp of different time generation successively respectively at each display unit.
Preferably, if any one the display controller second time in described at least two display controllers receives the described bus data frame corresponding with its unique described bus address that described timestamp high-speed generator sends, then show the timestamp corresponding with current described bus data frame with the display unit that any one display controller described connects in described array of display, otherwise the described timestamp before display all the time.That is each display unit shows the timestamp received separately successively all the time, until the timestamp again receiving a up-to-date generation then starts to show up-to-date timestamp.
Preferably, in described array of display, each display unit shows the described timestamp of different time generation respectively according to described display unit priority distributing order from left to right, from top to bottom.Because described timestamp is that described timestamp high-speed generator produced continuously every the scheduled time, the time value of timestamp constantly increases, according to array way, priority distributing order from left to right, from top to bottom shows respectively, can be convenient to determine effective timestamp (timestamp of maximum) fast when gathering graphical analysis like this, generally be positioned at the lower right corner of image, improve the efficiency of analyzing and processing.
Preferably, each display unit in described array of display is LCD display unit, and multiple LCD display unit forms LCD array of display according to ranks alignment.
Concrete, described array of display is alignd according to ranks by the LCD display unit of multiple very small dimensions, and be spliced into a compact LCD array regularly, Fig. 2 is the schematic diagram of LCD array.Referring to Fig. 1, timestamp panel (i.e. end-to-end video transmission delay measurements display unit) is made up of five parts such as LCD array, GPS time service clock, display controller, timestamp high-speed generator, buses.Each LCD display unit has separately independently display controller, and is linked together by bus and timestamp high-speed generator.Each display controller has unique bus address, obtains from bus the timestamp sending to this address from timestamp high-speed generator, and drives LCD display unit to demonstrate timestamp.GPS time service clock obtains external GPS signal, generates lock in time.Timestamp high-speed generator obtains lock in time from GPS time service clock, and according to the bus address of the display controller of LCD display unit, the timestamp sending generation in turn shows to corresponding LCD display unit.Timestamp high-speed generator is every 1/
f csecond produces a timestamp, gives the LCD display unit of specifying display through bus.Each LCD display unit can show corresponding timestamp value all the time, until display controller receives new timestamp or removes display command.Timestamp on LCD array is by sequencing display from left to right, from top to bottom.The minimum time granularity that timestamp array of display can provide is 1/
f c.Timestamp array of display can show multiple timestamp, and the timestamp of maximum is wherein called that effective time stabs.
Because the time-delay measuring method of the non-intrusive of routine is normally facing to clock or stopwatch acquisition time stamp.Because constantly transformation period stamp is presented at the same position of a display unit or the position of next-door neighbour, the different timestamp in front and back overlaps, and forms fuzzy timestamp image.The present invention devises timestamp array of display panel, at the timestamp that different position display is different, avoids at the quick Presentation Time Stamp in same position, and surrounding time stamp is overlapping, thus forms timestamp image clearly, improves the accuracy of time-stamp Recognition.Utilize that its measuring junction can generate more accurately to during end Video transmission system time delay, timestamp image more clearly, and then improve latency measurement precision, to meet the latency measurement required precision to the extremely sensitive processing system for video of time delay.
The present invention also provides a kind of end-to-end video transmission delay measurements system, comprising:
First measurement display unit, i.e. the end-to-end video transmission delay measurements display unit (also claiming timestamp panel, lower same) of above-described embodiment, for generating at transmitting terminal and show the timestamp of different time generation according to array way on described array of display;
First video acquisition unit (as video camera), for gathering the timestamp image frame that described first measures the different time generation that the array of display of display unit shows, is sent to video delivery network by described image frame compression coding generating video stream;
Described video delivery network, is connected with described first video acquisition unit, for transmitting described video flowing;
Video display unit (as LCD display), is connected with described video delivery network, for receiving described video flowing, decoding and show decoded image frame to described video flowing;
Second measures display unit, and to measure display unit identical with described first, and start with described first measurement mechanism simultaneously, for generate at receiving terminal and according to the timestamp of array way display different time generation on described array of display;
Second video acquisition unit (as video camera), records for gathering simultaneously the video information that described second measures the timestamp image frame of the different time generation that the array of display of display unit shows and the decoded image frame of described video display unit display.
Preferably, in one example, it is 3-5 minute that described second video acquisition unit collection recorded for the described second time of measuring the image frame video of display unit and described video display unit, can gather enough pictures like this for subsequent treatment.Second video acquisition unit also can preserve the video information of collection.
Analytic unit, the described second described video information measuring display unit and described video display unit for collecting described second video acquisition unit is decoded, each frame is saved as piece image, then in the picture described second measure the maximum very first time stamp of display unit extracted region, the second timestamp that described video display unit extracted region is maximum in the picture, the difference calculating stamp of the described very first time and the second timestamp is time delay measurement value.Described analytic unit can be any calculation element with video, image procossing.
The present invention utilizes described measurement display unit measuring junction to end Video transmission system time delay, can generate more accurately, timestamp image more clearly, and then improve latency measurement precision, to meet the latency measurement required precision to the extremely sensitive processing system for video of time delay, measuring system equipment of the present invention is simple simultaneously, and cost reduces greatly.
In order to improve certainty of measurement further, in one example, described analytic unit, also for calculating described time delay measurement value respectively to every two field picture, gets the mean value of multiple described time delay measurement value as transmission system time delay measurement value end to end.
Preferably, the frequency acquisition of described first video acquisition unit is
f s, the refresh rate of described video display unit is
f d, the frequency acquisition of described second video acquisition unit is
f r, wherein,
f d>=
f r>=
f s.
End-to-end video transmission delay measurements system of the present invention is illustrated below by an embodiment.
Referring to Fig. 3, measuring system of the present invention is made up of system under test (SUT) equipment and testing equipment two parts, testing equipment comprises transmitting terminal timestamp panel SSTPanel(i.e. the first measurement display unit, lower with), i.e. the second measurement display unit of destination time stamp panel RSTPanel(, lower with), receiving terminal video camera RCamera (i.e. the second video acquisition unit) three parts.System under test (SUT) equipment is mainly sending ending equipment video camera SCamera(i.e. the first video acquisition unit), the terminal equipment liquid crystal display DispLCD(of transmission network Transmission Networks, receiving terminal and video display unit).
Transmitting terminal SSTPanel generates continuous print Millisecond timestamp fast, and the array of display cells being presented at panel in turn gathers for sending ending equipment SCamera.SCamera gathers video image picture, compression coding generating video stream, and by video stream to transmission network Transmission Networks.In measuring process, SCamera, facing to SSTPanel capture video, has recorded the timestamp of constantly change on SSTPanel, has defined the input video picture with timestamp.Transmission Networks provides transmission channel for video flowing, and video is transferred to receiving terminal from transmitting terminal, completes the transmission of video data stream.DispLCD is receiving terminal, realizes video reception decoding display, the video pictures of decoding is presented to user, and in the process measured, DispLCD shows the video pictures with transmitting time stamp that transmitting terminal is brought.RSTPanel and SSTPanel function class seemingly, mainly generates continuous print Millisecond timestamp fast, and is presented in turn on panel for receiving terminal RCamera collection.RCamera is video camera, at receiving terminal simultaneously facing to DispLCD and RSTPanel fast recording from the timestamp of transmitting terminal and receiving terminal local time stamp.
The collection of making a start of tested transmission system is stabbed with transmitting time
t svideo pictures, receiving terminal decoding display, with the video pictures of transmitting time stamp, then to be stabbed with the time of reception of the local time stamp Display panel of receiving terminal
t rthe high frame rate camera RCamera of receiving end gathers display simultaneously, by analyzing video image, extracts
t swith
t rand computing time is poor, thus acquire the measured value of end-to-end transmission delay.The present invention calculates simply, precision is high, and measuring equipment is simple, and cost reduces greatly.
Concrete, in the present embodiment, SSTPanel and RSTPanel forms by the liquid crystal display of 500 very small dimensions, is arranged in 20 row, often row 25 display units.Liquid crystal display is of a size of wide 25.4 millimeters, high 14 millimeters.Time showing form is M.SS.XXX, and wherein M minute, SS are second, and XXX is millisecond, totally 8 characters, and the delay scope therefore measured can reach 10 minutes, meets existing all networks.Described bus uses CAN, and Bus Speed is 1Mbps.High speed time stamp generator realizes primarily of DSP, precise time timestamp value is obtained by serial port from GPS time service clock every 2 milliseconds, and the CAN Frame generated with object bus address, the display controller of the display unit of specifying is sent to by CAN.The difference of adjacent two timestamps is 2 milliseconds, therefore has clock frequency
f c=500Hz.
In the present embodiment, the resolution of the video camera SCamera of transmitting terminal is 1920 × 1080, frame per second
f s=60Hz, video delivery network Transmission Networks is DVB-T wireless transmitting system, comprises modulator and the power amplifier of making a start, antenna of making a start, receiving terminal antenna, receiving terminal demodulator, receiving terminal decoder (not shown).The resolution of the DispLCD display screen of receiving terminal is 1920 × 1080, refresh rate
f d=60Hz.The resolution of the video camera RCamera of receiving terminal is 1920 × 1080, frame per second
f r=60Hz.
Specific works process is as follows:
(1) system under test (SUT) is opened
Start SCamera, transmission network Transmission Networks, receiving device DispLCD respectively.
(2) testing equipment is started
Start SSTPanel and RSTPanel respectively, until all demonstrate timestamp, and DispLCD and RSTPanel is tightly put together side by side.
(3) transmitting terminal acquisition time stamp video
SCamera is placed on SSTPanel just before, observe SCamer view-finder, suitably adjust distance, make SSTPanel form picture comparatively clearly.SCamera starts to record the video with timestamp.
(4) receiving terminal acquisition time stamp video
When the picture of transmitting terminal timestamp panel SSTPanel is after DispLCD demonstrates, RCamera is placed on before RSTPanel and DispLCD, observe RCamera view-finder, adjust to suitable distance, make the picture of the picture of RSTPanel and DsipLCD form picture clearly at RCamera simultaneously.RCamera records 3-5 minute video, and preserves video file.
(5) analysis image calculating time delay CDL
The video that RCamera records is decoded, every frame is saved as piece image.According to the sequencing recorded, observe transmitting time stamp picture and the time of reception stamp picture of every two field picture.Because RCamera gathers the picture of RSTPanel and DispLCD simultaneously, therefore in the described image that the every frame preserved is corresponding, there is two regions, i.e. DispLCD imaging region and RSTPanel imaging region.In the image of the Video Quality Metric of RCamera collection, from the region of DispLCD, find maximum timestamp
t s, from RSTPanel region, find maximum timestamp
t r, the measured value of computing relay
delay=
t r-
t s.
In order to improve certainty of measurement further, from every two field picture, calculate a measured value
delay, get 100 two field pictures
delay, calculate their arithmetic average
as transmission system time delay CDL end to end.
Make calculating time delay CDL below and illustrating: due to the restriction by display control state switching delay, display frame does not complete instantaneously on the one hand, there is deferring procedure; On the other hand by the restriction of refresh rate, the picture of video display is visually continuous print, but is actually discrete, has certain time interval between adjacent two width pictures.Before display next frame picture, previous frame picture can rest on screen always.Therefore, can be regarded as pulse signal in interval at this moment, its amplitude remains unchanged.
Video acquisition process neither the completing of transient state sudden change.By the restriction of imaging photosensitive mechanism, need an exposure period when gathering picture, within the time of whole exposure, the CCD of video camera carries out photosensitive accumulation to the picture of shooting, and the namely process of charge accumulation, is similar to one-dimensional curve integration.If when the picture be taken does not have an acute variation, the picture of accumulation will constantly be strengthened, visually color burn.If when the picture be taken has an acute variation, the picture of accumulation exists overlapping, presents fuzzy picture.
The process of video acquisition and display is all the sampling process of the 2D signal to constantly change.If process is all discrete periodic process, because frequency can not be completely the same, and cannot precise synchronization be reached, then can there is sampling error.If there is a definitely accurate continuous time
t, frequency is
f isampled signal
s i, the cycle is 1/
f hhigh frequency period departure process
p hbe 1/ with the cycle
f llow-frequency cycle departure process
p l.Sampled signal
f ito the sampling of high and low frequency process as schematically shown in Figure 4.?
t mmoment,
s isimultaneously right
p hwith
p lsampling.?
t nmoment is observed
s ithe signal adopted, remains
p h?
t qthe value in moment,
p l?
t kthe value in moment, due to 1/
f l>=1/
f h, therefore obviously have Δ
t h≤ Δ
t l.During sampling keeps, even if be there occurs change by the number of accepting and believing, but sampled value still can not change thereupon, therefore can produce error.From the time, right
p hthe signal that process gathers is more close
t nthe value in moment, therefore time error is smaller.When
f hlarger, then the scope of biased error is then less.
At the timestamp panel SSTPanel of the transmitting terminal of measurement Video transmission system time delay, the frequency of clock is
f c, namely every 1/
f cgenerate a new timestamp second to be presented on position up-to-date on array of display.The frame per second of video camera SCamera is
f s, every 1/
f ssecond gathers a two field picture, the up-to-date time that logging timestamp panel shows to timestamp panel (namely first measuring display unit).The schematic diagram of gatherer process as shown in Figure 5.When camera video camera SCamera exists
t mmoment gathers image to timestamp panel, then the up-to-date timestamp obtained is on panel
t sthe time value of moment display, the error of generation is Δ
t s, its scope is 0≤Δ
t s<1/
f c.The timestamp video that SCamera gathers, after compression coding, forms video flowing and is admitted to transmission network.
At the timestamp panel RSTPanel of the receiving terminal of measurement Video transmission system time delay, the frequency of clock is also
f c, namely every 1/
f cgenerate a new timestamp second, be presented at up-to-date position.The refresh rate of receiving terminal decoding display DispLCD is
f d, namely every 1/
f dshow a two field picture second.The frame per second of video camera RCamera is
f r, namely every 1/
f rsecond gathers a two field picture to timestamp panel, the time that logging timestamp panel shows.Have under normal circumstances
f d>=
f r>=
f s, therefore the time renewal frequency of decoding on display screen is equivalent to
f s.That is, stabbing frequency in the effective time of receiving terminal display is frequency acquisition according to transmitting terminal video camera SCamera
f s.RCamera gathers the process of dual-time stamp as shown in Figure 6.RCamera exists
t wmoment gather RSTPanel timestamp actual be
t rthe timestamp that moment generates, error is Δ
t r=
t w-
t r, obviously have 0≤Δ
t r≤ 1/
f c.RCamera exists
t walthough the timestamp of the display screen DispLCD that the moment gathers is
t uthe timestamp that moment refreshes, but be actually
t pthe timestamp of moment decoding display.Namely
t umoment display timestamp with
t pthe timestamp in moment is consistent, because
f d>=
f s, so be belong to repeat display.Therefore error is Δ
t p=
t w-
t p, obvious 0≤Δ
t p≤ 1/
f s.
Receiving terminal RCamera gathers receiving terminal stamp local effective time from RSTPanel and DispLCD simultaneously and decoding shows the video pictures of imitating timestamp.Because
f d>=
f r>=
f s, so
t wthe timestamp that moment obtains from DispLCD should be
t uthe picture that moment refreshes, is in fact
t ptimestamp shown by the picture in moment.This timestamp is actual is equivalent to the transmitting time stamp of transmitting terminal, therefore complex chart 5 and Fig. 6 known, end to end time delay CDL can be calculated by following formula:
CDL=
T w -T m =(
T r +Δ
t r)
-(
T p +Δ
t p)
=(
T r +Δ
t r)
-(
T s +Δ
t s +Δ
t p)
= (
T r -T s )-(Δ
t p +Δ
t s -Δ
t r)
In fact, from collection RCamera collection picture, transmitting time stamp can only be obtained
t sstab with time of reception
t r.By
t swith
t rcalculate the measured value of end-to-end delay
delay:
Delay=
T r-
T s=CDL
+δ
Contrast above two formula can be found out, error is
δ=(Δ
t p +Δ
t s -Δ
t r), the generation of this error comes from SCamera, RCamera, DispLCD does not have precise synchronization, the change of transmission network, the change in location of sampled point and pulse starting point.In theory, the scope of this error is [-(1/
f c+
f s), 1/
f c+ 1/
f s).Error
δbe dynamic change, cause the CDL calculated to be constantly change.In order to reduce error, calculate multiple
delayarithmetic average
as the value of time delay CDL.
The present invention utilizes recurrent pulses sampling theory, analyzes the error of timestamp, establishes the precision 1/ of the Presentation Time Stamp of measure error scope and timestamp panel
f c(1/
f cless precision is higher), the frame per second of the video camera of transmitting terminal
f s, receiving terminal display screen refresh rate
f d, receiving terminal the frame per second of video camera
f rrelation.The present invention, by improving the precision of timestamp, adopts transmitting terminal video camera and the receiving terminal video camera of high frame per second, and receiving terminal adopts the display that refresh rate is high.
The present invention measures in display unit the array of display devising the display unit formation that can show multiple timestamp, at the timestamp that different position display is different, avoid at the quick Presentation Time Stamp in same position, surrounding time stamp is overlapping, thus form timestamp image clearly, improve the accuracy of time-stamp Recognition.
Utilize that its measuring junction can generate more accurately to during end Video transmission system time delay, timestamp image more clearly, and then improve latency measurement precision, to meet the latency measurement required precision to the extremely sensitive processing system for video of time delay, measuring system equipment of the present invention is simple simultaneously, and cost reduces greatly.
By reference to the accompanying drawings the specific embodiment of the present invention is described in detail above, but the present invention is not restricted to above-mentioned execution mode, in the spirit and scope situation of claim not departing from the application, those skilled in the art can make various amendment or remodeling.
Claims (10)
1. an end-to-end video transmission delay measurements display unit, it is characterized in that, comprise timestamp high-speed generator, described timestamp high-speed generator connects at least two display controllers, described at least two display controllers connect a display unit separately respectively, and described array of display cells arrangement forms array of display;
Described timestamp high-speed generator, for producing a timestamp lock in time every the scheduled time from the acquisition of GPS time service clock, sends the described timestamp of different time generation successively to described at least two display controllers; The wherein said scheduled time is Millisecond;
Described at least two display controllers, for obtaining the timestamp that sends from described timestamp high-speed generator thus driving described array of display;
Shown array of display, for showing the described timestamp of different time generation successively respectively at each display unit.
2. end-to-end video transmission delay measurements display unit according to claim 1, it is characterized in that, at least two display controllers described in described timestamp high-speed generator is connected by bus, described at least two display controllers have unique bus address separately;
Described timestamp high-speed generator is specifically for producing a timestamp lock in time every the scheduled time from the acquisition of GPS time service clock, each described timestamp is generated the bus data frame with described bus address, sends described bus data frame successively to described bus;
Described at least two display controllers, specifically for obtaining the corresponding described bus data frame that from described timestamp high-speed generator send unique with respective described bus address according to respective described bus address from described bus respectively, are resolved described bus data frame and are extracted timestamp wherein thus drive described array of display;
Shown array of display, for showing the described timestamp of different time generation successively respectively at each display unit.
3. end-to-end video transmission delay measurements display unit according to claim 2, it is characterized in that, if any one the display controller second time in described at least two display controllers receives the described bus data frame corresponding with its unique described bus address that described timestamp high-speed generator sends, then show the timestamp corresponding with current described bus data frame with the display unit that any one display controller described connects in described array of display, otherwise the described timestamp before display all the time.
4. the end-to-end video transmission delay measuring device according to any one of claim 1-3, it is characterized in that, in described array of display, each display unit shows the described timestamp of different time generation respectively according to described display unit priority distributing order from left to right, from top to bottom.
5. end-to-end video transmission delay measurements display unit according to claim 4, is characterized in that, each display unit in described array of display is LCD display unit, and multiple LCD display unit forms LCD array of display according to ranks alignment.
6. an end-to-end video transmission delay measurements system, is characterized in that, comprising:
First measures display unit, i.e. the end-to-end video transmission delay measurements display unit of any one of the claims 1-5, for generating at transmitting terminal and show the timestamp of different time generation according to array way on described array of display;
First video acquisition unit, for gathering the timestamp image frame that described first measures the different time generation that the array of display of display unit shows, is sent to video delivery network by described image frame compression coding generating video stream;
Described video delivery network, is connected with described first video acquisition unit, for transmitting described video flowing;
Video display unit, is connected with described video delivery network, for receiving described video flowing, decoding and show decoded image frame to described video flowing;
Second measures display unit, and to measure display unit identical with described first, and start with described first measurement mechanism simultaneously, for generate at receiving terminal and according to the timestamp of array way display different time generation on described array of display;
Second video acquisition unit, records for gathering simultaneously the video information that described second measures the timestamp image frame of the different time generation that the array of display of display unit shows and the decoded image frame of described video display unit display;
Analytic unit, the described second described video information measuring display unit and described video display unit for collecting described second video acquisition unit is decoded, each frame is saved as piece image, then in the picture described second measure the maximum very first time stamp of display unit extracted region, the second timestamp that described video display unit extracted region is maximum in the picture, the difference calculating stamp of the described very first time and the second timestamp is time delay measurement value.
7. end-to-end video transmission delay measurements system according to claim 6, is characterized in that, it is 3-5 minute that described second video acquisition unit collection recorded for the described second time of measuring the image frame video of display unit and described video display unit.
8. end-to-end video transmission delay measurements system according to claim 6, it is characterized in that, described analytic unit, also for calculating described time delay measurement value respectively to every two field picture, gets the mean value of multiple described time delay measurement value as transmission system time delay measurement value end to end.
9. end-to-end video transmission delay measurements system according to claim 6, is characterized in that, the frequency acquisition of described first video acquisition unit is
f s, the refresh rate of described video display unit is
f d, the frequency acquisition of described second video acquisition unit is
f r, wherein,
f d>=
f r>=
f s.
10. the end-to-end video transmission delay measurements system according to any one of claim 6-9, it is characterized in that, described first video acquisition unit and the second video acquisition unit are video camera, described video display unit is LCD display.
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