CN103905820A - Client side video quality self-adaption method and system based on SVC - Google Patents
Client side video quality self-adaption method and system based on SVC Download PDFInfo
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Abstract
The invention discloses a client side video quality self-adaption method and system based on an SVC. The method is used in the service that a video is downloaded online while played. The method includes the network bandwidth initial quality self-adaption step of forecasting the number of an initial downloading layer of a user side according to the code rate of each layer and the set preload cache time duration and downloading and caching video data corresponding to the forecasted number of the initial downloading layer, and the network bandwidth self-adaption step of forecasting the current video downloading speed of a user when the user plays the video according to the dynamic change of the size of data which have been cached but not been played yet at the user side, and regulating and optimizing the number of the video downloading layer of the user step by step according to the forecasted current video downloading speed of the user. By means of the client side video quality self-adaption method and system, dynamic quality self-adaption is conducted on the network bandwidth through relatively moderate and gradual quality regulation, and the smooth video quality is provided for the user.
Description
Technical field
The present invention relates to scalable video coding, quality adaptation, transmission of video, be specifically related to a kind of client video quality adaptive approach and system based on SVC.
Background technology
Along with the rapid rising of mobile Internet, and the promotion of the Internet, Broadcasting Cable Network, telecommunications network " integration of three networks " spring tide, following internet video stream media system will inevitably provide service towards isomerous environment.So-called " isomerous environment " both comprised the isomery of terminal, had the smart mobile phone, notebook, PC, CATV set-top-box of the termination property such as different resolution, disposal ability etc.; Also comprise the isomery of network, there is 3G, WiFi, Ethernet, cable television network of the network characteristics such as different access bandwidths, time delay, packet loss etc.Therefore, how for heterogeneous terminals provides adaptive video quality, and how on heterogeneous network, carrying out high efficiency transmission of video, is one of significant challenge of facing of internet video stream media technology.
At present, providing the traditional method of video stream media service towards isomerous environment is that same content is repeatedly encoded, and produces multiple video flowings with different code checks, the video flowing that user is different according to condition selective reception.But the way of this repeatedly coding can significantly increase the burden of video server, reduce the shared rate of data.In order to address the above problem, document H.Schwarz, D.Marpe, H.264/AVC standard.IEEE transactions on circuits and systems for video technology of and T.Wiegand.Overview of the Scalable Video Coding Extension of the, 2007,17 (9): scalable video coding (Scalable Video Coding, the SVC) technology of recording in 1103-1119 and the combination of Streaming Media are arisen at the historic moment.H.264/SVC video data is divided into a basal layer and several enhancement layers, and wherein basal layer provides the most basic viewing quality, and enhancement layer can be in time, space and three dimensions of quality the quality of augmented video.SVC technology can make same video content only just can meet the demand of different user in heterogeneous networks through first encoding, thereby reduces the burden of video server, improves the shared rate of data.Therefore the correlative study of, SVC being introduced to the stream media system under isomerous environment has caused the continuous concern of academia in recent years.
Than the stream media system of single code check, the advantage of the stream media system maximum based on SVC is to provide quality adaptation.Specifically, different users will obtain the different enhancing numbers of plies from streaming media server according to the ability of self and network condition.Quality adaptation is divided into two aspects: the firstth, at the beginning of user's incoming stream media system, can (specifically describe with reference to as Publication about Document: C.Hsu and M.Hefeeda.Achieving Viewing Time Scalability in Mobile Video Streaming Using Scalable Video Coding.In Proc.of ACM Multimedia Systems (MMSys'10) according to the battery electric quantity of self decoding capability, screen size, access network type, mobile terminal, Scottsdale, AZ, 2010:111-122.) etc. carry out initial mass self adaptation.The secondth, user carries out dynamic mass self adaptation according to the variation of network condition in the process of downloading.Comparatively speaking, the former is static, disposable, and the latter, be dynamic, in time, becomes, and is also the difficult point of research.Document M.Wien, R.Cazoula, A.Graffunder, A.Hutter and P.Amon.Real-time system for adaptive video streaming based on SVC.IEEE Transactions on Circuits and Systems for Video Technology.2007, 17:1227., document T.Schierl, C.Hellge, S.Mirta, K.Grueneberg, and T.Wiegand.Using is Scalable Video Coding (SVC) for Real Time Streaming in Wireless IP Networks.IEEE ISCAS H.264/AVC-based, New Orleans, LA, 2007:3455-3458. and document Y.Ding, J.Liu, D.Wang and H.Jiang.Peer-to-peer Video-on-Demand with Scalable Video Coding.Computer Communication, the framework of SVC stream media system has all been proposed for application scenarios separately in 2010, and carry out relevant research aspect the self adaptation of code check.Before H.264/SVC formulating, relevant research has been done by the academia just flatness of the layered video to plasticity (LayeredVideo) transmission.Wherein, document S.Nelakuditi, R.R.Harinath, E.Kusmierek, and Z.-L.Zhang.Providing Smoother Quality Layered Video Stream.Proc.10th Int ' Workshop Network and Operation System Support for Digital Audio and Video (NOSSDAV), June2000. propose the smoothness index (as avgrun) of layered video, and provided the adaptive transmission method that maximizes these indexs; Document R.Rejaie, M.Handley, and D.Estrin. " Quality adaptation for congestion controlled video playback over the internet ", Proc.SIGCOMM'99.1999:189-200. provided the friendly congestion control mechanism lower leaf of TCP video smooth transfer method, method hypothesis available bandwidth waveform is sawtooth waveforms, need to obtain in advance downloading rate with and the slope that increases in time.
Existing SVC video quality adaptive technique, mostly to suppose the current speed of download D that has obtained client by certain approach, then on this basis, can calculate the number of plies L that is applicable to transmission under current speed of download, method can be summed up as greatly: establish d
ibe i layer bit rate, front i layer total bitrate D
ifor
the number of plies L of client meets so: D
l≤ D < D
l+1although this method can be to the variation fast reaction of moment network condition, and calculate client be applicable to receive enhancement layer, advantage is the variation of the network bandwidth to do optimum prediction and self adaptation, but the defect of the method is not consider that user experiences.If network less stable, by the variation that causes receiving the number of plies frequently and moment is larger, like this, user watch the quality of video can be thereupon constantly, significantly change, reduce thereby cause user to experience greatly.
Summary of the invention
The object of the invention is to, the above-mentioned problems that exist for overcoming prior art,
For achieving the above object, the invention provides a kind of client video quality adaptive approach based on SVC, the method is broadcast business below for Online Video limit, and described method comprises:
Step 101) for to the adaptive step of network bandwidth initial mass, this step is specially: according to the initial download number of plies of the pre-buffer memory duration prediction user side of each layer bit rate and setting, and video data corresponding to the initial download number of plies that prediction is obtained downloaded buffer memory;
Step 102) for the step to network bandwidth self adaptive, this step is specially: the current video downloading rate of dynamic change predictive user of the data volume of according to user side buffer memory but not yet playing in the time of user's displaying video, and the current video speed of download progressively adjusted optimization user's of the user who obtains according to prediction video is downloaded the number of plies.
Above-mentioned steps 101) further comprise:
Step 101-1) set the lasting duration of pre-buffer memory and be: PRE_TIME, when initial, setting and downloading the number of plies is l=1, downloads the moment to be in fact made as t
0=0;
Step 101-2) download the video data of l layer in duration PRE_TIME, and the data of downloading are carried out to pre-buffer memory;
Step 101-3) after the pre-buffer memory of l layer video data finishes, if l < is L
min, forward 101-4 to); If l=L
max, represent that user has downloaded to the maximum layer of permission, forwards 102-5 to); If front l layer download time t
l> (D
l/ D
l+1) × PRE_TIME, forwards 102-5 to), t
lthe download time sum of l layer before representing;
Step 101-4) l=l+1 is set, forward 101-2 to);
Step 101-5) the initial download number of plies PRE_LAYER=l of the user side that obtains of record prediction;
Step 101-6) user side downloads the video data of pre-buffer memory PRE_LAYER layer;
Wherein, L
minrepresent the minimum number of plies of client video, L
maxrepresent the maximum number of plies of client video, and L
minand L
maxdetermined D in the initial mass self adaptation stage according to self decoding capability and screen size by user
ithe code check sum of i layer before representing, and 1≤L
min≤ L
max≤ L, L is the total layering number of user side video to be downloaded.
Above-mentioned steps 102) further comprise:
Step 102-1) " indicating device " using the dynamic change of data volume to be played in buffer memory in user terminal video playing process as downloading rate, be specially:
Work as t
downloadrepresent client point of current download time, t
decoderepresent the current play time of client, in client-cache, video duration to be played is: t
buf=t
download-t
decode, by t
bufas downloading rate " indicating device ";
Step 102-2) when downloading rate indicator t
bufwhile reducing to first threshold, receive the number of plies and switch, reduce one deck; When downloading rate indicator t
bufwhile being increased to Second Threshold, receiving the number of plies and switch, increase one deck;
Wherein, the first pre-threshold value is less than the second pre-threshold value.
Described first threshold is: Δ × (D
l-1/ D
l), Second Threshold is: Δ+INC_TIME;
Wherein, the value of the downloading rate " indicating device " when Δ is last video quality switching in buffer memory, and the initial value of downloading rate " indicating device " is PRE_TIME, INC_TIME is add factor, Di represents the code check of front i layer, supposes that video is divided into L layer, and to establish i layer video code check be d
i, front i layer bit rate is:
Wherein, 1≤i≤L, total number of plies that L is foradownloaded video.
The value of above-mentioned add factor INC_TIME is 10s.
Also provide a kind of client video quality Adaptable System based on SVC based on said method the present invention, described system comprises:
Pre-cache module, for according to the initial download number of plies of the pre-buffer memory duration prediction user side of each layer bit rate and setting, and video data corresponding to the initial download number of plies that prediction is obtained downloaded buffer memory; ;
Dynamic mass adaptation module, for in the time that user plays according to buffer memory but the current video downloading rate of dynamic change predictive user of the data volume of not yet playing, and the current video speed of download progressively adjusted optimization user's of the user who obtains according to prediction video is downloaded the number of plies.
Above-mentioned pre-cache module further comprises:
Initial value is set submodule, sets the lasting duration of pre-buffer memory and is: PRE_TIME, and the initial number of carrier layer is at present l=1, current download time is made as t
0=0;
Download submodule, download the video data of l layer in duration PRE_TIME, and pre-buffer memory;
Judgement submodule, after finishing, makes the following judgment decision-making for the pre-buffer memory of l layer video data that carrier module is downloaded instantly:
If l < is L
min, drive and increase progressively submodule; If l=L
max, represent that user has downloaded to the maximum layer of permission, drives the initial reception number of plies to set submodule; If front l layer download time t
l> (D
l/ D
l+1) × PRE_TIME, if it is overtime to represent that user continues to download the meeting of " l+1 " layer, drives the initial reception number of plies to set submodule;
Increase progressively submodule, for l=l+1 is set, and again start download submodule;
The initial reception number of plies is set submodule, the initial download number of plies obtaining for recording prediction, i.e. PRE_LAYER=l;
Wherein, L
minexpression client is accepted the minimum number of plies of video, L
maxexpression client is accepted the maximum number of plies of video, and L
minand L
maxdetermined D in the initial mass self adaptation stage according to self decoding capability and screen size by user
ithe code check sum of i layer before representing.
Above-mentioned dynamic mass adaptation module further comprises:
Set submodule, for setting buffer memory video duration to be played be: t
buf=t
download-t
decode, wherein, t
downloadrepresent current download time point, t
decoderepresent current play time;
Receive the number of plies and adjust submodule, the t obtaining for setting submodule
bufas " indicating device " of user unloading speed, work as t
bufwhile being reduced to the first setting threshold, the reception number of plies of user side reduces one deck, works as t
bufwhile being increased to the second setting threshold, user side receives the number of plies increases one deck, and the first pre-threshold value is less than the second pre-threshold value.
Above-mentioned the first setting threshold is: Δ × (D
l-1/ D
l);
The second setting threshold is: Δ+INC_TIME;
Wherein, t when Δ is last video quality switching in buffer memory
bufvalue, its initial value is PRE_TIME, INC_TIME is add factor, D
ithe code check sum of i layer before representing;
Described D
idefinite mode be: suppose that video is divided into L layer, and establish the i(1≤i≤L) layer video code check is d
i, front i layer bit rate is
。
The value of above-mentioned add factor INC_TIME is 10s.
The technical problem to be solved in the present invention is to provide a kind of new client video quality adaptive approach based on SVC, and dynamic change that can either network bandwidth adaptive can make again user obtain relatively preferably video-see quality simultaneously.
In sum: the present invention not only before broadcasting the pre-buffer memory by the short time network bandwidth is carried out to initial mass self adaptation, and " indicating device " using the dynamic change of data volume to be played in buffer memory in playing process as downloading rate, by quality adjustment relative mitigation, level, the network bandwidth is carried out to dynamic mass self adaptation, for user provides level and smooth video quality.The present invention can either network bandwidth adaptive dynamic change, can change when violent and make the variation of video quality as far as possible level and smooth and stable in network state again simultaneously, experience thereby make user obtain relatively preferably video-see.The present invention realized a set of H.264/SVC Streaming Media prototype system, by simulate different network bandwidth environment verified method can be in the situation that not affecting user's viewing experience the dynamic change of network bandwidth adaptive.And from fineness and smoothness two aspects of video, the performance of adaptive approach is assessed.
Compared with prior art, technical advantage of the present invention is:
1) the present invention carries out dynamic mass self adaptation by quality adjustment relative mitigation, level to the network bandwidth, for user provides level and smooth video quality.2) dynamic change that the present invention can either network bandwidth adaptive, can change when violent and make the variation of video quality as far as possible level and smooth and stable in network state again simultaneously, experiences thereby make user obtain relatively preferably video-see.
Brief description of the drawings
Fig. 1 is pre-buffer memory schematic diagram provided by the invention;
Fig. 2 is dynamic mass adaptive approach schematic diagram provided by the invention;
Fig. 3 is the flow chart of the client video quality adaptive approach based on SVC provided by the invention;
Fig. 4 is SVC Streaming Media prototype system provided by the invention;
The client software module that Fig. 5 embodiment of the present invention provides;
Fig. 6 is that download and the broadcasting number of plies that emulation obtains changes schematic diagram (network is more stable, and initial bandwidth is lower) with downloading rate;
Fig. 7 is that download and the broadcasting number of plies that emulation obtains changes schematic diagram (network is more stable, and initial bandwidth is medium) with downloading rate;
Fig. 8 is that download and the broadcasting number of plies that emulation obtains changes schematic diagram (unstable networks, initial bandwidth is lower) with downloading rate;
Fig. 9 is that download and the broadcasting number of plies that emulation obtains changes schematic diagram (unstable networks, initial bandwidth is medium) with downloading rate;
Figure 10 is the impact of add factor INC_TIME value of the present invention on video average bit rate;
Figure 11 is the impact of add factor INC_TIME value of the present invention on switching times.
Embodiment
Below in conjunction with the drawings and specific embodiments, elaborate the method Online Video limit and broadcast below the workflow in business.
The quality adaptation method based on buffer memory that the present invention proposes has been taken into account objective network bandwidth self adaptive and subjective viewing experience.Quality adaptation method based on buffer memory is divided into two stages: pre-buffer memory (Pre-Buffer) stage and dynamic mass self adaptation (Dynamic Quality Adaptation) stage.The pre-buffer memory stage is by pre-one section of video of buffer memory before broadcasting, makes to watch more smooth, and predicts the initial reception number of plies, and the network bandwidth is carried out to initial mass self adaptation; The dynamic mass self adaptation stage in the time playing according to buffer memory but current downloading rate is predicted in the dynamic change of the data volume of not yet playing, and change and download the number of plies relatively lenitively, the network bandwidth is carried out to dynamic self-adapting.
Describing before adaptive approach in this paper, supposing that user has carried out initial mass self adaptation according to self decoding capability, screen size etc., and determined the maximum number of plies L of user's receiver, video
maxwith minimum number of plies L
minif user's original video to be played has been divided into L layer, 1≤L
min≤ L
max≤ L.
I, pre-buffer memory stage
The video of pre-buffer memory certain hour section before video playback, as duration PRE_TIME=5s, 10s...... the download number of plies with initial network bandwidth match according to speed of download code check prediction relative to each layer.Specifically, given PRE_TIME duration, client starts successively to download each layer data from basal layer, until overtime.
Pre-buffer memory concrete grammar is described below:
1) set the duration PRE_TIME of pre-buffer memory, the initial number of carrier layer is at present made as l=1, and current download time is made as t
0=0;
2) download the data in the l layer PRE_TIME time;
3) after the pre-buffer memory of l layer finishes, if l < is L
min, forward 4 to); If l=L
max, the maximum layer that downloads to permission is described, forward 5 to); If front l layer download time t
l> (D
l/ D
l+1) × PRE_TIME, meaning may be overtime if download l+1 layer again, forwards 5 to);
4) l=l+1, forwards 2 to);
5) the initial download number of plies that l predicts, i.e. PRE_LAYER=l.
As Fig. 1, suppose that video has divided 3 layers, and each layer bit rate is equal, and establishes PRE_TIME=5s, download after ground floor download time t
1=2s < (D
1/ D
2) × PRE_TIME=2.5s, continues to download; Download after the second layer, due to t
2=4s > (D
2/ D
3) × PRE_TIME ≈ 3.3s, has not had to download the 3rd layer enough remaining times, the user's who finally predicts initial reception number of plies PRE_LAYER=2.
Suppose that video is divided into L layer, and to establish i layer video code check be d
i, front i layer bit rate is:
It is more smooth that the advantage of pre-buffer memory is not only to make to watch, and play detection network situation, predicts the effect of the initial reception number of plies.
The dynamic mass self adaptation of II based on buffer memory
After pre-buffer memory finishes, the download module of client continues downloading data, and player starts to obtain from reception buffer zone data decode and plays.In order to adapt to the dynamic change of the network bandwidth, client every request download certain section grow the data of (being made as the duration of a GOP in prototype system below) more in short-term before, need to carry out dynamic mass self adaptation to determine the download number of plies.Than previous download period, receiving the number of plies may switch also and may not switch, and consider user's viewing experience, only in the time of the marked change that detects the network bandwidth, just change and receive the number of plies, and the quality of Switch Video too continually not, each amplitude of switching should be as far as possible little simultaneously, and the present invention is made as one deck, but actual conditions are not limited in this kind of set-up mode.
Suppose t
downloadcurrent download time point, t
decodecurrent play time, video duration to be played in buffer memory so:
t
buf＝t
download-t
decode
In video download and playing process, t
bufalong with downloading rate changes and dynamic change.Suppose that video code rate is D, so in the time of downloading rate d > D, t
bufconstantly increase; And in the time of d < D, t
bufconstantly reduce.Dynamic mass adaptive approach in this paper utilizes t well
bufas " indicating device " of downloading rate.Work as t
bufwhile reducing (increase) to certain threshold value, receive the number of plies and reduce (increase) one deck.Obviously, choosing of switching threshold requires careful consideration, if switching threshold is static, and so in the time that the network bandwidth is shaken, t
bufmay, in certain Near Threshold fluctuation, cause quality frequently to switch.Given this, switching threshold is also dynamic change, and the correlation of twice switching before and after utilizing.While supposing last switching, t in buffer memory
buf=Δ, the number of plies after switching is l layer.Before GOP of every download, according to current t
bufsize judge whether switch receive the number of plies.Wherein the initial value of Δ is PRE_TIME.
1) if t
buf≤ Δ × (D
l-1/ D
l), and l > L
min, now receive the number of plies and should reduce one deck.Δ is updated to t simultaneously
buf.
2) if t
buf>=Δ+INC_TIME, and l < L
max, now receiving the number of plies should increase one deck, and Δ is updated to t
buf.Prototype system verification portion is below from the impact of fineness and the smoothness two aspect discussion of video the value that the compared add factor INC_TIME performance on adaptive approach.
The reception number of plies of having described Fig. 2 reduces one deck, constant and three kinds of situations of increase one deck.Only have and continue and stably when speed of download, instead of moment ground is while increasing (or reducing), just correspondingly cumulative rises of data (or minimizing) to be played in buffer memory are to a certain amount of, and receiving the number of plies just can corresponding change.
Shown in Fig. 3, this figure is the flow chart of the client video quality adaptive approach based on SVC provided by the invention, specifically comprises following steps:
Step 100) determine the maximum number of plies and the minimum number of plies of receiver, video;
Step 101) determine pre-buffer memory duration, download base layer data, and make to download the number of plies and carry out from increasing;
Step 102) download from the data that increase rear respective layer;
Step 103) download next layer data according to current download time, each layer bit rate and pre-buffer memory duration prediction and whether can exceed default buffer memory duration, if not overtime, download the number of plies from increasing 1, return to step 102); Otherwise enter lower step;
Step 104) user side starts to play the above-mentioned video of pre-buffer memory, and a definite fixing download period, enters the dynamic mass self adaptation stage;
Step 105) client continuation foradownloaded video data, and in the time of each end cycle, check the number of plies that whether needs to switch user side receiver, video;
Whether current cache video duration is not more than first threshold value that while switching by the last time, buffer memory video duration and each layer bit rate determine, if be not more than, the receiver, video number of plies reduces 1 layer; Otherwise, then judge whether current cache video duration is not less than buffer memory video duration and second threshold value that parameter determines while switching by the last time, if be not less than, the receiver, video number of plies increases by 1 layer; Otherwise the receiver, video number of plies is constant.
Wherein, described first threshold value is: Δ × (D
l-1/ D
l).
Second threshold value is: Δ+INC_TIME.
Specific embodiment
I prototype system
As shown in Figure 4, we have realized a set of SVC Streaming Media prototype system, and system is made up of a streaming media server and multiple client.Server end has been deposited SVC layered video file and strategy file.Native system is not considered the quality adaptation of time dimension, and this is that the hierarchical file that therefore server end is deposited is only distinguished space layer and quality layers in order to facilitate decoder to decode to fix frame per second.Server end and client functionality are as described below respectively:
Server end:
Document layered function---scan SVC original coding file and extract each NAL by separator, be stored in corresponding hierarchical file according to the space layer under it (Did) and quality layers (Qid), generate corresponding strategy file simultaneously.Each layer data of same number of frames is by DQid(DQid=Did<<4+Qid) interdepend from small to large.Strategy file has recorded Did and Qid and the each GOP(Group of Pictures under total hierarchy number, each hierarchical file) relativity shift position in hierarchical file, so that the data that client is downloaded request position.Wherein GOP is the basic structure of carrying out inter prediction, supposes that original video has divided T time horizon, and the contained frame number of each GOP is 2T-1.
Upload function---transmit corresponding strategy file or individual-layer data according to the download request of client.
Client:
Client limit is first from streaming media server download policy file and analyze accordingly, then foradownloaded video data, and be sent to decoder real-time decoding and play.SVC real-time decoder is at open source software Open SVC Decoder
[8]basis on rewrite and form, and done a simple player interface with microsoft foundation class storehouse MFC, the operation such as support to play, suspend, stop.Client is divided into video quality self adaptation and decoding two large modules in software module, as Fig. 5.
Video quality adaptation module---this module is divided into be downloaded and analysis strategy file, initial mass self adaptation and three submodules of dynamic mass self adaptation.Download also analysis strategy file submodule and be responsible for downloading and analysis strategy file, to obtain SVC document layered information, then notify decoder initialization; Maximum layer L when first initial mass self adaptation submodule is downloaded according to client end capacity and user preferences etc. are definite
maxwith smallest tier L
min, then carry out foregoing pre-caching method prediction initial network bandwidth, pre-buffer memory finishes rear triggering decoder module decoding; Dynamic mass self adaptation submodule downloads by dynamically adjusting the variation that the number of plies adapts to the network bandwidth.
Decoder module---according to the hierarchical information of Analytical Index file acquisition, decoder is carried out to initialization, wait for that pre-buffer memory finishes rear beginning and cyclically from download buffer, extract each layer data of a GOP, reconfigure rear decoding by decoding order and play.
II method validation
Table 1 video raw information and point layer bit rate
This part verifies the validity of the quality adaptation method that the present invention proposes by transmit encoded video H.264/SVC in prototype system.Test video information is in table 1, and adopting the software JSVM of SVC official is 3 quality layers by Video coding, and GOP size is 8.In order to support better client adaptive approach to the abandoning arbitrarily of enhancement data in decoding aspect, coded system adopts MGS(medium size quality grading coding), each layer totally video code rate in table 1.
In data downloading process, use speed limit software NetLimiter to carry out downloading speed limiting to the SVC player of client, the bandwidth of simulating respectively two class access networks changes.1) network is more stable, and bandwidth changes relatively mitigation, and changes in amplitude is less, is similar to the situation of fixed network; 2) unstable networks, dynamic is stronger, changes yardstick larger, be similar to mobile network's situation, this carries out 30 times random speed limit in video display process by NetLimiter, the average speed limit cycle is that 10s realizes, and speed limit is chosen at random between 35KB/s～200KB/s.Pre-cache-time PRE_TIME is made as 10s.Fig. 6 is given different speed limit condition to Fig. 9, and the download that test obtains in prototype system and the broadcasting number of plies change schematic diagram (INC_TIME value is all 10s) with downloading rate.Due to the cushioning effect of buffer memory, broadcast layer number curve relatively lags behind in time than downloading number of plies curve.
Can find out from Fig. 6-9, the download of initial a period of time (≤10s) and the broadcasting number of plies are all 0, and now client is being carried out the pre-buffer memory of data.When initial downloading rate lower (as Fig. 6 and Fig. 8), pre-buffer memory predict that the initial download number of plies obtaining is 1 layer, and when downloading rate medium (as Fig. 7 and Fig. 9), the initial download number of plies that buffer memory predicts is in advance 2 layers.Therefore,, from experimental result, pre-buffer memory can predict the reception number of plies suitable with initial bandwidth.
After pre-buffer memory, dynamic mass adaptive approach starts to play a role.When the network bandwidth is lower, download the number of plies and correspondingly reduce to ensure the fluency of watching, and downloading rate is while continuing to increase, downloading the number of plies increases to give user quality meticulousr video.Analysis chart 6 and Fig. 7 because network change is milder, have only carried out the quality adjustment of (3 times and 5 times) seldom several times in playing process, and user has obtained extraordinary viewing experience under event of bandwidth limitation.Even and unstable at the network bandwidth, in the more severe situation of network jitter (as Fig. 8 and Fig. 9), pre-buffer memory and dynamic mass adaptive approach have also played extraordinary effect, switching times (9 times and 8 times) is slightly many while only stablizing than network, makes user watch smoother video.This has also just verified no matter be in network stabilization or unsettled situation, and dynamic mass adaptive approach can both switch by relatively less level the network of self adaptation dynamic change.
Next the relatively impact of the value of add factor INC_TIME on adaptive approach performance.In can layered video transmission system, the final viewing experience of user be to be determined by the fluency of video, fineness and three factors of smoothness.In this paper discussion process, downloading rate nearly all, on basal layer code check, therefore watches fluency aspect can not be affected; Video fineness can on average be play code check by video
weigh, in general, the Y-PSNR (PSNR) that the higher user of meaning of average bit rate receives video is higher, and the quality of picture is meticulousr; Video smoothness can be weighed by switching times (S) and these two indexs of switching amplitude.Quality adaptation method in this paper is only adjusted one deck in the time that level switches at every turn, and switching amplitude is minimum.Therefore,, we mainly assess the impact of INC_TIME value adaptive approach performance from average broadcasting code check and switching times (frequency) two aspects.Fig. 8 and Fig. 9 have provided respectively under different speed limit conditions (comprising the stability of network and different initial bandwidths) video quality switching times when INC_TIME gets respectively 5s, 10s, 15s, 20s, 25s, 30s and have on average play code check, and speed limit condition corresponding to test result being linked up by same broken line in figure is all the same.As can be seen from the figure, under which kind of speed limit condition, video average bit rate and quality switching times all increase monotone decreasing with INC_TIME.This is because INC_TIME is larger, and data have just been downloaded more in advance, and the rest network bandwidth that user does not use is just more, therefore on average plays code check lower; INC_TIME value is larger simultaneously, and level switching is subject to instantaneous network variable effect less, and therefore switching times is fewer.From average bit rate, INC_TIME is larger, and video quality is poorer; And from switching times, INC_TIME is larger, video is more level and smooth on the contrary.But as can be seen from the figure, INC_TIME is approximately linear on the impact of video average bit rate in terms of overall, and be nonlinear on the impact of switching times, in 10s time, switching times increases sharply and reduces with INC_TIME, and in the time being greater than 10s, switching times curve is tending towards smooth, continue to increase INC_TIME video smoothness is promoted not quite, and video average bit rate continues to reduce thereupon.Therefore, in actual SVC stream media system, balance video average bit rate and switching frequency (number of times), it is a preferably value that INC_TIME is made as to 10s left and right, the in the situation that of being so no matter or unstable networks stable at network, user can both obtain relatively level and smooth and meticulous video-see and experience.
In a word, the quality adaptation method based on buffer memory that the present invention proposes has been taken into account objective network bandwidth self adaptive and subjective viewing experience.The method is divided into two stages: pre-buffer memory and dynamic mass self adaptation.Pre-buffer memory carries out initial mass self adaptation to the network bandwidth; The dynamic mass self adaptation network bandwidth is carried out dynamic self-adapting.
It should be noted that, embodiment of the present invention of above introduction provide a kind of method of the client video quality adaptive approach based on SVC, and the explanation of this embodiment is just for helping to understand method of the present invention and core concept thereof and unrestricted.One of ordinary skill in the art should be appreciated that any amendment to technical solution of the present invention or is equal to and substitute the spirit and scope that do not depart from technical solution of the present invention, and it all should be encompassed within the scope of claim of the present invention.
Claims (10)
1. the client video quality adaptive approach based on SVC, the method is broadcast business below for Online Video limit, and described method comprises:
Step 101) for to the adaptive step of network bandwidth initial mass, this step is specially: according to the initial download number of plies of the pre-buffer memory duration prediction user side of each layer bit rate and setting, and video data corresponding to the initial download number of plies that prediction is obtained downloaded buffer memory;
Step 102) for the step to network bandwidth self adaptive, this step is specially: the current video downloading rate of dynamic change predictive user of the data volume of according to user side buffer memory but not yet playing in the time of user's displaying video, and the current video speed of download progressively adjusted optimization user's of the user who obtains according to prediction video is downloaded the number of plies.
2. the client video quality adaptive approach based on SVC according to claim 1, is characterized in that described step 101) further comprise:
Step 101-1) set the lasting duration of pre-buffer memory and be: PRE_TIME, when initial, setting and downloading the number of plies is l=1, downloads the moment to be in fact made as t
0=0;
Step 101-2) download the video data of l layer in duration PRE_TIME, and the data of downloading are carried out to pre-buffer memory;
Step 101-3) after the pre-buffer memory of l layer video data finishes, if l < is L
min, forward 101-4 to); If l=L
max, represent that user has downloaded to the maximum layer of permission, forwards 101-5 to); If front l layer download time t
l> (D
l/ D
l+1) × PRE_TIME, forwards 101-5 to), t
lthe download time sum of l layer before representing;
Step 101-4) l=l+1 is set, forward 101-2 to);
Step 101-5) the initial download number of plies PRE_LAYER=l of the user side that obtains of record prediction;
Step 101-6) user side downloads the video data of pre-buffer memory PRE_LAYER layer;
Wherein, L
minrepresent the minimum number of plies of client video, L
maxrepresent the maximum number of plies of client video, and L
minand L
maxdetermined D in the initial mass self adaptation stage according to self decoding capability and screen size by user
ithe code check sum of i layer before representing, and 1≤L
min≤ L
max≤ L, L is the total layering number of user side video to be downloaded.
3. the client video quality adaptive approach based on SVC according to claim 1, is characterized in that described step 102) further comprise:
Step 102-1) " indicating device " using the dynamic change of data volume to be played in buffer memory in user terminal video playing process as downloading rate, be specially:
Work as t
downloadrepresent client point of current download time, t
decoderepresent the current play time of client, in client-cache, video duration to be played is: t
bub=t
download-t
decode, by t
bufas downloading rate " indicating device ";
Step 102-2) when downloading rate indicator t
bufwhile reducing to first threshold, receive the number of plies and switch, reduce one deck; When downloading rate indicator t
bufwhile being increased to Second Threshold, receiving the number of plies and switch, increase one deck;
Wherein, the first pre-threshold value is less than the second pre-threshold value.
4. the client video quality adaptive approach based on SVC according to claim 3, is characterized in that,
Described first threshold is: Δ × (D
l-1/ D
l), Second Threshold is: Δ+INC_TIME;
Wherein, Δ is the value of the last video quality downloading rate " indicating device " in buffer memory while switching, and the initial value of downloading rate " indicating device " is PRE_TIME, and INC_TIME is add factor, D
ithe code check of i layer before representing, supposes that video is divided into L layer, and to establish i layer video code check be d
i, front i layer bit rate is:
Wherein, 1≤i≤L, total number of plies that L is foradownloaded video.
5. the client video quality adaptive approach based on SVC according to claim 4, is characterized in that, the value of described add factor INC_TIME is 10s.
6. the client video quality Adaptable System based on SVC, described system comprises:
Pre-cache module, for according to the initial download number of plies of the pre-buffer memory duration prediction user side of each layer bit rate and setting, and video data corresponding to the initial download number of plies that prediction is obtained downloaded buffer memory; ;
Dynamic mass adaptation module, for in the time that user plays according to buffer memory but the current video downloading rate of dynamic change predictive user of the data volume of not yet playing, and the current video speed of download progressively adjusted optimization user's of the user who obtains according to prediction video is downloaded the number of plies.
7. the client video quality Adaptable System based on SVC according to claim 6, is characterized in that, described pre-cache module further comprises:
Initial value is set submodule, sets the lasting duration of pre-buffer memory and is: PRE_TIME, and the initial number of carrier layer is at present l=1, current download time is made as t
0=0;
Download submodule, download the video data of l layer in duration PRE_TIME, and pre-buffer memory;
Judgement submodule, after finishing, makes the following judgment decision-making for the pre-buffer memory of l layer video data that carrier module is downloaded instantly:
If l < is L
min, drive and increase progressively submodule; If l=L
max, represent that user has downloaded to the maximum layer of permission, drives the initial reception number of plies to set submodule; If front l layer download time t
l> (D
l/ D
l+1) × PRE_TIME, if it is overtime to represent that user continues to download the meeting of " l+1 " layer, drives the initial reception number of plies to set submodule;
Increase progressively submodule, for l=l+1 is set, and again start download submodule;
The initial reception number of plies is set submodule, the initial download number of plies obtaining for recording prediction, i.e. PRE_LAYER=l;
Wherein, L
minexpression client is accepted the minimum number of plies of video, L
maxexpression client is accepted the maximum number of plies of video, and L
minand L
maxdetermined D in the initial mass self adaptation stage according to self decoding capability and screen size by user
ithe code check sum of i layer before representing.
8. the client video quality Adaptable System based on SVC according to claim 6, is characterized in that, described dynamic mass adaptation module further comprises:
Set submodule, for setting buffer memory video duration to be played be: t
buf=t
download-t
decode, wherein, t
downloadrepresent current download time point, t
decoderepresent current play time;
Receive the number of plies and adjust submodule, the t obtaining for setting submodule
bufas " indicating device " of user unloading speed, work as t
bufwhile being reduced to the first setting threshold, the reception number of plies of user side reduces one deck, works as t
bufwhile being increased to the second setting threshold, user side receives the number of plies increases one deck, and the first pre-threshold value is less than the second pre-threshold value.
9. the client video quality Adaptable System based on SVC according to claim 8, is characterized in that, described the first setting threshold is: Δ × (D
l-1/ D
l);
The second setting threshold is: Δ+INC_TIME;
Wherein, t when Δ is last video quality switching in buffer memory
bufvalue, its initial value is PRE_TIME, INC_TIME is add factor, D
ithe code check sum of i layer before representing;
Described D
idefinite mode be: suppose that video is divided into L layer, and establish the i(1≤i≤L) layer video code check is d
i, front i layer bit rate is
10. the client video quality adaptive approach based on SVC according to claim 9, is characterized in that, the value of described add factor INC_TIME is 10s.
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