CN100514963C - Method for producing RTP time stamp on gateway - Google Patents
Method for producing RTP time stamp on gateway Download PDFInfo
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Abstract
Said invention designs video coding technique and method, when gateway operate mode is transparent transmission mode, directly extracting time information from H,324 vision data stream and corresponding to RTP, ensuring accurately filling in RTP time stamp to make H,323 video terminal accurately representation video frequency after receiving video frequency package according to video frequency sampling time, when said H,323 network and,324 network all adopts H,263 encoded mode encoded mode , said time information extracted from H,263 frame head time information domain, when said H,323 network and H,324 network all adopts MPEG -4 coding decoding mode , gateway generating RTP time stamp from video frequency object plane group end absolute time messages and video frequency object plane end time increment messages.
Description
Technical field
The video traffic that the present invention relates to network H.323 and H.324 change between the network, H.263 the system that relates in particular to adopts or in these two kinds of coding and decoding video modes of MPEG-4, and gateway generates the method for RTP time stamp when carrying out network H.324 to the protocol conversion of network H.323.
Background technology
Increasingly mature along with 3G technology, the function of support is enriched perfect day by day, and except the challenge of self-technique, the 3G commercial network also will be faced with the problem with other various existing network intercommunications.In the existing network, the development of packet network is particularly swift and violent, and legacy network is substituted by new packet network gradually, realizes that the intercommunication of 3G network and existing packet network is a current key point.Multimedia service is the bright spot of 3G, and wherein video traffic is behaved and know most, and the commercial at present or commercial 3G network of examination all provides video traffic.Simultaneously, H.323 network is as a kind of packet network, rely on himself technical advantage also can support the multimedia service that enriches, existing the H.323 terminal of a large amount of various support video traffics in this network, is exactly wherein a kind of such as the Web conference that carries under the Windows operating system (NetMeeting).Yet, because the Media Stream coded system of transmitting in 3G communication network and the packet communication network is different, therefore the binding site at 3G network and packet network need carry out the conversion of Media Stream, realize this conversion equipment we be referred to as gateway, can realize the gateway of video traffic media stream transition, be called VIG (Video Interworking Gateway, the video transfer gateway), the position of VIG in network as shown in Figure 1, VIG is at 3G network with H.323 between the network packet network, the 3G network terminal sends to after H.323 the video image of terminal is encoded as frame of video, RNC in network (Radio NetvorkControler successively, radio network controller), GMSC (Gate Way Mobile Switching Center gateway MSC) is sent to VIG, VIG will receive frame of video and be converted to the H.323 frame of video of network format, send to H.323 terminal through IP (Internet Protocol, Internet protocol) network again.
3G video terminal (hereinafter be called for short " terminal ") and H.323 terminal defer to respectively ITU-T H.324 with ITU-T agreement H.323, unify to be referred to as in this article " H.324 terminal " and " H.323 terminal ".H.324 terminal is in the video call of terminal H.323 at one time, and VIG finishes H.324 protocol family and the H.323 conversion between the protocol family, realizes H.324 terminal and the H.323 intercommunication of terminal.
The working method of VIG can be divided into two kinds: transparent transmission mode and encoding and decoding conversion mode.No matter be H.324 terminal or H.323 terminal, generally can adopt H.263 with these two kinds of coding and decoding video modes of MPEG-4 in a kind of.When the two parties terminal adopted identical code encoding/decoding mode, VIG was operated under the transparent transmission mode, and promptly VIG only need do conversion to the encapsulation format of video data stream according to agreement, and does not need the load of video data stream is done conversion.When the two parties terminal adopts different code encoding/decoding mode, VIG is operated under the encoding and decoding conversion mode, be that VIG had both needed according to agreement the encapsulation format of video data stream to be done conversion, also need to the load of video data stream do H.263 and two kinds of coding and decoding video modes of MPEG-4 between change.When video data transmits, need carry out the encapsulation of RTP bag according to the RFC1889 agreement on packet network H.323.Be about to the continuous video data stream that terminal H.324 sends and be divided into the RTP packet that is suitable for the packet network transmission, corresponding RTP packet header is added in each packet front, is used for carrying some relevant informations of this packet, for example: temporal information etc.
Carrying out the principle that video data stream cuts apart is: each frame of video is placed in the packet as far as possible to be transmitted.In the header packet information of RTP bag, time stamp (Timestamp) territory of four bytes is arranged, be commonly referred to " RTP time stamp ", be used for representing the temporal information of this RTP bag.In order to fill in the RTP time stamp exactly, guarantee can reappear frame of video according to the time of video sampling exactly after terminal is H.323 received video packets, must find from video data stream extracting time information and correspond to the method for RTP time stamp.Prior art adopts following two kinds of methods extracting time information and correspond to the RTP time stamp from video data stream:
Prior art one: the direct output time information of Video Codec
Because VIG possesses the coding and decoding video translation function,, in the process of encoding and decoding, can access temporal information so VIG needs embedded Video Codec.VIG extracts frame data according to frame triggering encoder and encodes from buffer memory, when encoding frame data and output, increase the RTP time stamp increment of a frame period correspondence at every turn, is filled up in the RTP packet header.
There is following shortcoming in this method: the needs startup expends the Video Codec of a large amount of system processing powers, and only is applicable to the encoding and decoding conversion mode.Because when using the transparent transmission mode, under normal circumstances can not need to start Video Codec, so the method is to transparent transmission mode and inapplicable yet.If under the transparent transmission mode, still adopt this method, can expend a large amount of system processing powers, the number of active lanes that causes single chip to be handled seriously descends, and equipment cost rises, and this all is unacceptable for operator and equipment supplier.
Prior art two: directly get system time and be converted to the RTP time stamp
In the time of VIG output RTP bag, directly current system time is converted to the RTP time stamp, fills in the RTP packet header.For example: the resolution of RTP time stamp is 90k, and the method for conversion is: the resolution * 90k of RTP time stamp=current system time/system time.
There is following shortcoming in this method: be subjected to the influence of several factors, the moment that VIG finishes a frame video coding is indefinite, harvest the time of whole frame of video such as side joint H.324, the moment of VIG scheduling video coding, finish time of a frame video coding or the like, cause the time interval between per two frame of video of output unfixing, sometimes longer, sometimes short, this phenomenon is called as " shake ", after shake occurring, H.323 terminal just can't be recovered video flowing smoothly, shows as video image that the user sees smoothness inadequately.
As seen, in the prior art, when gateway uses the transparent transmission mode, can not accurately produce the RTP time stamp, causing H.323, video terminal can not reappear frame of video according to the time of video sampling after receiving video packets exactly.
Summary of the invention
Technical problem to be solved by this invention is: when the working method of VIG is the transparent transmission mode, provide a kind of from video data stream H.324 direct extracting time information and correspond to the method for RTP time stamp, guarantee to fill in the RTP time stamp exactly, making H.323, video terminal can reappear frame of video according to the time of video sampling after receiving video packets exactly.
A kind of method that on gateway, generates the RTP time stamp, described gateway connects the H.323 network that uses different agreement bunch respectively and network H.324, when this gateway H.324 the video data stream that sends of network cut apart and when converting the RTP packet of Network Transmission H.323 to, in the packet header of described RTP packet, fill in the RTP time stamp; When network H.323 and H.324 network all adopt H.263 code encoding/decoding mode or network and when H.324 network all adopts the MPEG-4 code encoding/decoding mode H.323, gateway from described H.324 Internet video data flow with the identification information of time correlation in extracting time information, and generate described RTP time stamp by corresponding calculated according to different code encoding/decoding modes.
When described H.323 network with when H.324 H.263 network all adopts code encoding/decoding mode, described temporal information is extracted from the temporal information territory of frame head H.263.
When the every increase of described temporal information N, current RTP time stamp equals previous RTP time stamp and adds N RTP time stamp increment, each RTP time stamp increment equals the frame period time and multiply by the resolution of RTP time stamp, the described frame period time equals the inverse of system's frame frequency, wherein, N is the integer more than or equal to 1.
When described H.323 network with when H.324 network all adopts the MPEG-4 code encoding/decoding mode, gateway generates the RTP time stamp and comprises the following steps:
A, gateway extract absolute time information from the video object plane group head that receives, this absolute time information is converted into RTP benchmark time stamp and preservation;
B, gateway from the video object plane head that receives extraction time increment information, this incremental time information is converted into RTP time stamp increment;
C, RTP time stamp increment is added the above RTP benchmark time stamp generate the required RTP time stamp of RTP packet, and upgrade described RTP benchmark time stamp with this RTP time stamp.
Among the described step a: described RTP benchmark time stamp is obtained by the resolution that described absolute time information multiply by the RTP time stamp; Among the described step b: described RTP time stamp increment equals the resolution that described incremental time information multiply by the RTP time stamp after divided by the resolution of incremental time information field again, and the resolution of described incremental time information field is extracted from object video level head by gateway.
Use the method for the invention can receive following beneficial effect: when the working method of VIG during as the transparent transmission mode, without Video Codec, direct extracting time information and correspond to the RTP time stamp from the video data stream that terminal is H.324 sent, improved the disposal ability of the video transfer gateway that is operated under the transparent transmission mode greatly, the shake of effectively having avoided the VIG system to introduce, make H.323 terminal recover video flowing smoothly, make the user see smooth video image.
Description of drawings
The position view of Fig. 1 video gateway in network.
Embodiment
When the method for the invention can make the working method of VIG be the transparent transmission mode, without Video Codec, direct extracting time information and correspond to the RTP time stamp from the video data stream that terminal is H.324 sent, improved the disposal ability of the video transfer gateway that is operated under the transparent transmission mode greatly, the shake of effectively having avoided the VIG system to introduce, make H.323 terminal recover video flowing smoothly, make the user see smooth video image.Describe in detail with specific embodiment below:
Embodiment one: code encoding/decoding mode H.263
When H.263 system adopted code encoding/decoding mode, the form of RFC2190 agreement regulation was adopted in RTP packet header, and wherein the resolution of RTP time stamp is 90k.According to the regulation of agreement H.263, in the data flow of video encoder output, the beginning of each two field picture has some to identify the data of this frame information, is called as " frame head ".A temporal information (TR:Temporal Reference) territory is arranged in frame head, the every frame of numerical value wherein increases by 1, so can find the corresponding relation of temporal information territory and RTP time stamp by frame frequency, every increase by one frame, the increment of RTP time stamp calculates by following formula 1:
The resolution of the increment=frame period of RTP time stamp (second) * RTP time stamp ... 1
For example: when system adopted 30 usually said frame frequencies, frame frequency was (30k/1001) frame/second, was spaced apart 1001/30k second between promptly per two frames.When corresponding to resolution and be the RTP time stamp of 90k, the RTP time stamp should increase 1001/30k*90k=3003 by every frame, that is: the every increase by 1 of TR, and the RTP time stamp increases by 3003, if increase N, then the RTP time stamp increases N doubly 3003.
Embodiment two: the MPEG-4 code encoding/decoding mode
When system adopted the MPEG-4 code encoding/decoding mode, the form of RFC3016 agreement regulation was adopted in RTP packet header, and wherein the resolution of RTP time stamp is 90k.In MPEG-4 coding and decoding video agreement, the content of image is divided into some object videos, and one or some objects are belonged to some levels or plane.So in the data flow of MPEG-4 video encoder output, under similar H.263 code encoding/decoding mode the frame head of every frame data, head also has levels, first-class other identification information in plane, relevant with temporal information has: object video level (VOL:Video Object Layer) head, video object plane group (GOV:Group of Video Object Plane) head, video object plane (VOP:Video ObjectPlane) head, export according to particular order by video encoder, wherein the notion (specifically please refer to the MPEG-4 related protocol) that video object plane can corresponding " frame ".
An absolute time information (time_code) territory is arranged in the GOV head, with hour (time_code_hours) territory, minute (time_code_minutes) territory and second (time_code_seconds) domain identifier absolute time, the i.e. sampling time of these data wherein.An incremental time information (vop_time_increment) territory is arranged in the VOL header, this incremental time be and previous VOL or VOP between the time interval, constantly decide according to real data sampling, the resolution in this territory (vop_time_increment_resolutino) obtains in the VOL head.Before each VOP may be previous VOP, also may be a GOV.When being previous VOP before, the time value of current VOP is that the time value of previous VOP adds the incremental time that current VOP carries; When being GOV before, the time value of current VOP adds the incremental time that current VOP carries for the absolute time information time corresponding value that this GOV carries, promptly receive an object GOV at every turn, the temporal information in absolute time information (time_code) territory in this GOV was forced as the fiducial time that produces the RTP time stamp, when receiving a VOP, to add the temporal information of fiducial time with the incremental time information in this VOP as the generation RTP time stamp of this VOP, once more with this temporal information as fiducial time, next like this to as if during VOP, with this time serves as that basis its increment information that carries of increase calculates, next to liking GOV, be forced to fiducial time once more, concrete computational methods are divided into following three steps:
Obtain the method for RTP time stamp under the MPEG-4 code encoding/decoding mode:
1, when decoder is received one VOL, at first obtain the resolution of incremental time information field in the VOL head, and to establish benchmark RTP time stamp be old_time, the RTP time stamp that will produce is new_time.
2, when a GOV occurring, be converted to the system RTP time stamp, calculate by formula 2 according to its absolute time information that carries:
((time_code_hours*3600)+(time_code_minutes*60)+time_code_seconds)*M ...2
Wherein: M is the resolution of RTP time stamp, for example: 90k.With result of calculation as the benchmark time stamp and be saved in old_time.
3, when a VOP occurring, then obtain new_time, calculate by formula 3 according to old_time:
new_time＝old_time+((vop_time_increment/vop_time_increment_resolutino)
*M)...3
Wherein: M is the resolution of RTP time stamp, for example: 90k.
With the new_time that calculates RTP time stamp, and after the VOP packing sent, deposit new_time in old_time and upgrade the benchmark time stamp as packing VOP.
The above only is a preferred implementation of the present invention; should be pointed out that for those skilled in the art, under the prerequisite that does not break away from the principle of the invention; can also make some improvements and modifications, these improvements and modifications also should be considered as protection scope of the present invention.
Claims (5)
1, a kind of method that on gateway, generates the RTP time stamp, described gateway connects the H.323 network that uses different agreement bunch respectively and network H.324, when this gateway H.324 the video data stream that sends of network cut apart and when converting the RTP packet of Network Transmission H.323 to, in the packet header of described RTP packet, fill in the RTP time stamp; It is characterized in that: when network H.323 and H.324 network all adopt H.263 code encoding/decoding mode or network and when H.324 network all adopts the MPEG-4 code encoding/decoding mode H.323, gateway from described H.324 Internet video data flow with the identification information of time correlation in extracting time information, and generate described RTP time stamp by corresponding calculated according to different code encoding/decoding modes.
2, the method for claim 1 is characterized in that: when described H.323 network with when H.324 H.263 network all adopts code encoding/decoding mode, described temporal information is extracted from the temporal information territory of frame head H.263.
3, method as claimed in claim 2, it is characterized in that: when the every increase of described temporal information N, current RTP time stamp equals previous RTP time stamp and adds N RTP time stamp increment, each RTP time stamp increment equals the frame period time and multiply by the resolution of RTP time stamp, the described frame period time equals the inverse of system's frame frequency, wherein, N is the integer more than or equal to 1.
4, the method for claim 1 is characterized in that: when described H.323 network with when H.324 network all adopts the MPEG-4 code encoding/decoding mode, gateway generates the RTP time stamp and comprises the following steps:
A, gateway extract absolute time information from the video object plane group head that receives, this absolute time information is converted into RTP benchmark time stamp and preservation;
B, gateway from the video object plane head that receives extraction time increment information, this incremental time information is converted into RTP time stamp increment;
C, described RTP time stamp increment is added the above RTP benchmark time stamp generate the required RTP time stamp of RTP packet, and upgrade described RTP benchmark time stamp with this RTP time stamp.
5, method as claimed in claim 4 is characterized in that:
Among the described step a: described RTP benchmark time stamp is obtained by the resolution that described absolute time information multiply by the RTP time stamp;
Among the described step b: described RTP time stamp increment equals the resolution that described incremental time information multiply by the RTP time stamp after divided by the resolution of incremental time information field again, and the resolution of described incremental time information field is extracted from object video level head by gateway.
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| CNB2004101040591A CN100514963C (en) | 2004-12-31 | 2004-12-31 | Method for producing RTP time stamp on gateway |
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| AU2008242129B2 (en) * | 2007-04-24 | 2011-11-17 | Nokia Technologies Oy | Signaling of multiple decoding times in media files |
| CN101505420B (en) * | 2008-12-02 | 2011-01-26 | 深圳市同洲电子股份有限公司 | Encapsulation method for video compression data |
| CN101873549B (en) * | 2010-05-26 | 2013-08-21 | 姜红志 | Point-to-point transmission method for mobile video information adopting real-time flow transport protocol |
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