CN106603518A - Time stamp generating method and time stamp generating device of real-time transmission protocol system - Google Patents

Abstract

The invention discloses a time stamp generating method and a time stamp generating device of a real-time transmission protocol system. When system time is not modified, a time difference between a current time value and a last time value is calculated, and the time difference is added to a last time output value to be used as a current time output value. When time hopping occurs, the time difference is not calculated, and the last time difference is added to the last time output value to be used as the current time output value. A time output value of a current data frame is multiplied by a data sampling rate to acquire the time stamp of the current data frame, and therefore a problem of time stamp hopping caused by the modification of the system time is solved, and the generating error of the time stamp is reduced.

Description

Time stamp generation method and device for a real-time transport protocol system

technical field

The present application relates to the field, in particular to a method and device for generating a time stamp of a real-time transport protocol system.

Background technique

The timestamp reflects the sampling instant of the first byte of data in the RTP packet. The initial value of the timestamp at the beginning of a session is also randomly selected. Even when no signal is sent, the value of the timestamp will continue to increase over time. Timestamps are used by the receiving end to know exactly which data block should be restored at what time, eliminating jitter in transmission. Timestamps can also be used to synchronize sound and images in video applications.

In the prior art, there are generally two ways to obtain the time stamp. The first method: Randomly generate the timestamp of the initial frame of the video stream, denoted as T0, and calculate the timestamp increment according to the frame rate and video sampling rate. For example: the video sampling rate is 90000, the frame rate is 25, the RTP timestamp unit is 1/90000, the time interval of each frame is 0.04 seconds, the RTP timestamp increment=90000×0.04=3600, recorded as Delta=3600, after , for each frame i (i is a natural number greater than 0), the corresponding time stamp Ti=Ti-1+Delta. The second method: when the video encoder compiles a frame of data, use the system function to obtain the time difference between the current time and January 1, 1970, which is recorded as D0, and the unit is second; convert this value into RTP time stamp. For example: the video sampling rate is 90000, and the RTP timestamp unit is 1/90000, then the RTP timestamp T0=D0×90000, and then the timestamp of each frame is obtained cyclically according to the above method, namely: Ti=Di×90000.

The above two methods have the following problems: The first method is an ideal method. In practical applications, the video encoder cannot guarantee that the time used to encode each frame of video data is fixed at 0.04 seconds, so the actual value of Delta will vary with time. As for the change, if the Delta is fixed at 3600, the error will accumulate after a long time of application, and the error will become larger and larger, which will eventually cause the client to receive the video stream and the decoding will be abnormal and the stream will be cut off. The second method is used more in practical applications. It actually takes the actual time corresponding to the encoding of each frame of data (relative to the time difference on January 1, 1970), and there will be no error accumulation. However, this The problem with this method is that when the system time is changed, the obtained timestamp will also jump accordingly, which will cause the client to receive the video stream and decode it abnormally and the stream will be cut off.

To sum up, there is no better time stamp generation method in the prior art, which can solve the problem of the time stamp jumping due to the modification of the system time.

Contents of the invention

The present application provides a time stamp generation method and device for a real-time transport protocol system, which can solve the problem of time stamp jumps caused by modification of system time, and reduce time stamp generation errors.

According to the first aspect of the present application, the present application provides a method for generating a time stamp of a real-time transport protocol system, comprising: obtaining the time value of the current data frame and the time value of the previous data frame of the current data frame; Calculating a first difference D _i between the time value of the current data frame and a preset time and a second difference D _i-1 between the time value of the previous data frame of the current data frame and a preset time; According to the absolute value |D _i -D _i-1 | of the difference between the first difference and the second difference, it is judged whether the system time jumps; if not, D _i -D _{i -1} as the first backup difference Delta, the first backup difference Delta and the time output value Out _i-1 of the previous data frame are added to obtain the time output value Out _i of the current data frame; if so, then obtain The previous data frame of the previous data frame is used as a third data frame, and the time value of the previous data frame and the time value of the third data frame are obtained respectively; the time value of the current data frame is calculated respectively The second difference D _i-1 between the time value of the previous data frame and the preset time and the third difference D _i-2 between the time value of the third data frame and the preset time; the D _{i- 1} -D _i-2 is used as the second backup difference Delta', and the second backup difference Delta' is added to the time output value Out _i-1 of the previous data frame to obtain the time output value Out of the current data frame _i ; multiplying the time output value Out _i of the current data frame with the sampling rate of the data to obtain the timestamp of the current data frame.

According to the second aspect of the present application, the present application provides a time stamp generation device of a real-time transport protocol system, including: an acquisition unit, configured to acquire the time value of the current data frame and the time value of the previous data frame of the current data frame Time value; the first difference calculation unit is used to calculate the first difference D _i between the time value of the current data frame and the preset time and the time value of the previous data frame of the current data frame The second difference D _i-1 with the preset time; the absolute value judgment unit is used to determine the absolute value |D _i -D according to the difference between the first difference and the second difference _i-1 | Judging whether the system time jumps; the first time output value calculation unit is used to use D _i -D _i-1 as the first backup difference when the judgment result of the absolute value judgment unit is no Value Delta, add the time output value Out _i-1 of described first spare difference Delta and previous data frame, obtain the time output value Out _i of current data frame; When the judgment result of the value size judging unit is yes, the previous data frame of the previous data frame is obtained as the third data frame, and the time value of the previous data frame and the time value of the third data frame are respectively obtained. Time value; the second difference calculation unit is used to calculate the second difference D i-1 between the time value of the previous data frame of the current data frame and the preset time and the second difference D _i-1 of the third data frame The third difference D _i-2 between the time value and the preset time; the second time output value calculation unit is used to use D _i-1- D _i-2 as the second backup difference Delta', and the first Two standby difference Delta' and the time output value Out _i-1 of the previous data frame are added to obtain the time output value Out _i of the current data frame; the timestamp generating unit is used for the time output value of the current data frame Out _i is multiplied by the sampling rate of the data to get the timestamp of the current data frame.

The time stamp generation method and device of the real-time transmission protocol system of the present application obtain the time value of the current data frame and the time value of the previous data frame of the current data frame, and calculate the time value and preset time of the current data frame respectively The first difference D _i of the current data frame and the second difference D _i-1 between the time value of the previous data frame of the current data frame and the preset time, according to the difference between the first difference and the second difference The absolute value of the value|D _i -D _i-1 |judging whether the system time jumps, if not, then use D _i -D _i-1 as the first backup difference Delta, and the first backup difference Delta and Add the time output value Out _i-1 of the previous data frame to obtain the time output value Out _i of the current data frame; if so, obtain the time value of the previous data frame of the current data frame and the first two frames of the current frame respectively For the time value of the data frame, calculate the second difference D _i-1 between the time value of the previous data frame of the current data frame and the preset time and the second difference between the time value of the previous two data frames and the preset time Three difference values D _i-2 ; use D _i-1- D _i-2 as the second backup difference Delta', add the second backup difference Delta' to the time output value Out _i-1 of the previous data frame , to get the time output value Out _i of the current data frame. Finally, the time output value Out _i of the current data frame is multiplied by the sampling rate of the data to obtain the time stamp of the current data frame, which solves the problem of the time stamp following the jump caused by the modification of the system time and effectively reduces the time stamp. Build error.

Description of drawings

The above and/or additional aspects and advantages of the present invention will become apparent and comprehensible from the description of the embodiments in conjunction with the following drawings, wherein:

Fig. 1 is the flow chart of the time stamp generating method of the real-time transport protocol system of the embodiment of the present application;

FIG. 2 is a schematic structural diagram of a time stamp generating device of a real-time transport protocol system according to an embodiment of the present application;

FIG. 3 is another schematic structural diagram of a time stamp generation device of the real-time transport protocol system according to the embodiment of the present application.

detailed description

The present invention will be further described in detail below through specific embodiments in conjunction with the accompanying drawings. The present application provides a time stamp generation method and device for a real-time transport protocol system, which can reduce time stamp generation errors.

Embodiment one:

Please refer to FIG. 1. FIG. 1 is a flow chart of the method of Embodiment 1 of the present application. As shown in FIG. 1, the embodiment of the present application provides a timestamp generation method for a real-time transport protocol system, which may specifically include the following steps:

S101. Obtain the time value of the current data frame and the time value of the previous data frame of the current data frame.

S102. Calculate respectively the first difference D _i between the time value of the current data frame and the preset time and the second difference D _i-1 between the time value of the previous data frame of the current data frame and the preset time.

S103. According to the absolute value |D _i -D _i-1 | of the difference between the first difference and the second difference, it is judged whether the system time jumps, if not, execute steps S104 and S109, if so, Then execute steps S105-S109.

The judging process may specifically be: judging whether the absolute value |D _i -D _i-1 | of the difference between the first difference and the second difference is greater than a preset value, if so, it means The time has jumped, if not, it means that the system time has not jumped.

Preferably, the preset value is 2S. That is, if the difference is greater than 2S, it means that the system time jumps. If it is less than 2 seconds, the default system time does not jump.

S104. Using D _i -D _i-1 as the first backup difference Delta, adding the first backup difference Delta to the time output value Out _i-1 of the previous data frame to obtain the time output value Out of the current data frame _i .

S105. Obtain a previous data frame of the previous data frame as a third data frame, and respectively obtain a time value of the previous data frame and a time value of the third data frame.

The above step S105 is to obtain the data frames of the first two frames of the current data frame, and use the i-th data frame to represent the current data frame, then the previous data frame of the above-mentioned previous data frame is the i-2th data frame. For the convenience of subsequent description, the previous data frame of the previous data frame is expressed as a third data frame.

S106. Calculate respectively the second difference D i-1 between the time value of the previous data frame of the current data frame and the preset time and the third difference D _{i -1} between the time value of the third data frame and the preset time ₂ .

S107. Using the difference between D _i-1- D _i-2 as the second backup difference Delta', adding the second backup difference Delta' to the time output value Out _i-1 of the previous data frame to obtain the current The time output values Out _i of the data frame.

S108. Multiply the time output value Out _i of the current data frame by the sampling rate of the data to obtain the time stamp of the current data frame.

In an embodiment, the method of the present application further includes: acquiring a time difference D ₀ between the time value of the zeroth data frame and a preset time, and using D ₀ as the time output value of the zeroth data frame.

During initial encoding, D ₀ is used as the time output value of the first data frame. It can be understood that the time output values of subsequent frames are all calculated on the basis of the time output values of the previous frame.

Embodiment two:

An embodiment of the present application provides a method for generating a time stamp of a real-time transport protocol system, which may specifically include the following steps:

S201. Initially, when the video encoder encodes the 0th frame of video data frame, it obtains the time difference D ₀ between the current time T0 and the preset time Tb as a time reference point, and at the same time outputs the current time value Out ₀ =D ₀ , that is, the time reference point D ₀ is output as the time output value Out ₀ of the initial data frame.

The preset time Tb may be, for example, January 1, 1970, which is used in this example for introduction. It can be understood that the preset time is used as a reference time. In this example, the specific time point of the preset time Tb can also be other date and time, such as January 1, 1971, specifically when setting the preset time Tb , the preset time can be taken to the millisecond level according to actual needs and calculation accuracy, but it is worth pointing out that in this example, the preset time Tb remains unchanged throughout the calculation process.

S202. Obtain the time difference between the time value Ti of the current data frame and the preset time Tb to obtain the first difference Di; obtain the time value Ti' of the previous data frame of the current data frame and the first difference between the preset time Tb Two differences D _i-1 .

In this example, the system is currently encoding to the fifth frame data frame as an example for illustration. It can be understood that this example is also applicable to the timestamp generation method of each data frame after the fifth frame and each data frame before the fifth frame.

In the above step S202, the time difference between the time value Ti of the current data frame and the preset time Tb is obtained, and the first difference D _i is obtained as an example: the time value T5 and the preset time Tb of the fifth frame data frame are obtained to obtain the first difference D ₅ .

In the above step S202, the second difference D _i-1 between the time value Ti' of the previous data frame of the current data frame and the preset time Tb is obtained as an example: the time value T4 and the preset time value T4 of the fourth frame data frame are obtained. Assuming a time difference of time Tb, the second difference D ₄ is obtained.

S203. According to the absolute value of the difference between the first difference D _i and the second difference D _i-1 |D _i -D _i-1 |, determine whether the system time jumps, if not, execute the step S204-S205 and step 210, if yes, execute steps S206-S210.

An example of the process of judging whether the system time jumps in the above step S203 is: according to the absolute value of the difference between the first difference D ₅ and the second difference D ₄ |D ₅ -D ₄ | jump occurs.

S204. Use D _i -D _i-1 as the first backup difference Delta.

S205. Add the first standby difference Delta to the time output value Out _i-1 of the previous data frame to obtain the time output value Out _i of the current data frame.

According to the actual application scenario, it can be: calculate the first difference D ₅ between the time value of the fifth frame data frame and January 1, 1970, and calculate the difference between the time value of the fourth frame data frame and January 1, 1970 The first difference D ₄ between.

The above steps S204-S205 are: taking the value of D ₅ -D ₄ as the first backup difference value Delta.

Add Delta to the time output value Out ₄ of the fourth data frame to obtain the time output value Out ₅ of the current data frame. That is: Out ₅ =Out ₄ +Delta =Out ₄ +D ₅ -D ₄ .

S206. Obtain a previous data frame of the previous data frame as a third data frame, respectively obtain the time value of the previous data frame and the time value of the third data frame.

In the application scenario of this embodiment, step S206 is to acquire the third data frame, as the third data frame, acquire the time value of the third data frame and the time value of the fourth data frame.

S207. Calculate respectively the second difference D i-1 between the time value of the previous data frame of the current data frame and the preset time and the third difference D _{i -1} between the time value of the third data frame and the preset time ₂ .

In the application scenario of this embodiment, the above step S207 is: obtain the time difference between the time value T4 of the fourth frame data frame and the preset time Tb, obtain the second difference D ₄ , and obtain the time value of the third frame data frame The time difference between the value T3 and the preset time Tb to obtain the third difference D ₃ .

S208. Use D _{i-1 -} D _i-2 as the second backup difference Delta'.

S209. Add the time output value Out _i-1 of the previous data frame to the second spare difference Delta' to obtain the time output value Out _i of the current data frame.

According to the actual application scenario, it can be: calculate the second difference D ₄ between the time value of the fourth frame data frame and January 1, 1970, and calculate the difference between the time value of the third frame data frame and January 1, 1970 The third difference D ₃ between.

The above steps S208-S209 are: taking the value of D ₄ -D ₃ as the second spare difference value Delta'.

Add Delta' to the time output value Out ₄ of the fourth data frame to obtain the time output value Out ₅ of the current data frame. That is: Out ₅ =Out ₄ +Delta'. That is, Out ₅ =Out ₄ +D ₄ −D ₃ .

S210. Multiply the time output value Out _i of the current data frame by the sampling rate of the data to obtain the time stamp of the current data frame.

Assuming that the time stamp is T _C and the sampling rate is f, taking the calculation of the time stamp of the fifth frame as an example, step S210 may be:

When the system time does not change, T _C =Out ₅ ×f=(Out ₄ +D ₅ -D ₄ )×f

When the system time is changed, T _C =Out ₅ ×f=(Out ₄ +D ₄ -D ₃ )×f

Embodiment three:

Please refer to FIG. 2. FIG. 2 is a schematic structural diagram of Embodiment 2 of the present application. As shown in FIG. 2, the embodiment of the present application provides a timestamp generating device for a real-time transport protocol system, which may include:

The acquiring unit 30 is configured to acquire the time value of the current data frame and the time value of the previous data frame of the current data frame.

The first difference calculation unit 31 is used to calculate the first difference D _i between the time value of the current data frame and the preset time and the time value and preset time value of the previous data frame of the current data frame The second difference in time D _i-1 .

The absolute value judging unit 32 is configured to judge whether the system time jumps according to the absolute value |D _i −D _i-1 | of the difference between the first difference and the second difference.

The first time output value calculation unit 33 is used to use D _i -D _i-1 as the first backup difference Delta when the judgment result of the absolute value judgment unit 32 is No, and use the first backup difference Delta It is added to the time output value Out _i-1 of the previous data frame to obtain the time output value Out _i of the current data frame.

The time value unit 34 is used to obtain the previous data frame of the previous data frame as the third data frame when the judgment result of the absolute value judgment unit 32 is yes, and respectively obtain the previous data frame The time value of and the time value of the third data frame.

The second difference calculation unit 35 is used to calculate the second difference D _i-1 between the time value of the previous data frame of the current data frame and the preset time and the time value of the third data frame respectively A third difference D _i-2 from the preset time.

The second time output value calculation unit 36 is used to use D _i-1- D _i-2 as the second backup difference Delta', and compare the second backup difference Delta' with the time output value Out of the previous data frame _{Add i-1} to get the time output value Out _i of the current data frame.

A time stamp generating unit 37, configured to multiply the time output value Out _i of the current data frame by the sampling rate of the data to obtain the time stamp of the current data frame.

In one embodiment, the absolute value judgment unit 30 is specifically used for:

Judging whether the absolute value |D _i -D _i-1 | of the difference between the first difference and the second difference is greater than a preset value, if yes, it means that the system time jumps, if not , it means that the system time has not jumped.

Preferably, the preset value is 2S.

In one embodiment, as shown in FIG. 3 , the device of this embodiment further includes: an initial acquisition unit 38, configured to acquire the time difference D ₀ between the time value of the zeroth frame data frame and the preset time, and D ₀ is used as the zeroth frame The time output value of the frame data frame.

The time stamp generation method and device of the real-time transport protocol system of the present application, when the system time has not been modified, calculate the time difference between this time and the last time value, and add the time difference to the last time output value as this time Time output value. If the time jumps, the time difference is no longer calculated, and the time difference calculated last time is added to the last time output value as the current time output value. Finally, the time output value of the current data frame is multiplied by the sampling rate of the data to obtain the time stamp of the current data frame, which solves the problem of the time stamp following the jump caused by the modification of the system time and reduces the generation error of the time stamp.

The above content is a further detailed description of the present invention in conjunction with specific embodiments, and it cannot be assumed that the specific implementation of the present invention is limited to these descriptions. Those of ordinary skill in the technical field to which the present invention belongs can also make some simple deduction or replacement without departing from the concept of the present invention.

Claims (8)

1. A timestamp generating method of a real-time transport protocol system, characterized in that, comprising: Obtain the time value of the current data frame and the time value of the previous data frame of the current data frame; respectively calculating the first difference D _i between the time value of the current data frame and the preset time and the second difference D _i-1 between the time value of the previous data frame of the current data frame and the preset time ; Judging whether the system time jumps according to the absolute value |D _i -D _i-1 | of the difference between the first difference and the second difference; If not, D _i -D _i-1 is used as the first backup difference Delta, and the first backup difference Delta is added to the time output value Out _i-1 of the previous data frame to obtain the current data frame Time output value Out _i ; If so, then obtain the previous data frame of the previous data frame as a third data frame, respectively obtain the time value of the previous data frame and the time value of the third data frame; Calculate the second difference D _i-1 between the time value of the previous data frame of the current data frame and the preset time and the third difference D between the time value of the third data frame and the preset time _i-2 ; Using D _i-1- D _i-2 as the second backup difference Delta', adding the second backup difference Delta' to the time output value Out _i-1 of the previous data frame to obtain the current data frame Time output value Out _i ; The time output value Out _i of the current data frame is multiplied by the sampling rate of the data to obtain the time stamp of the current data frame. 2. The time stamp generation method of the real-time transport protocol system as claimed in claim 1, is characterized in that, the absolute value |D according to the size of the difference between the first difference and the second difference _i –D _i-1 |Judging whether the system time jumps includes: Judging whether the absolute value |D _i -D _i-1 | of the difference between the first difference and the second difference is greater than a preset value, if yes, it means that the system time jumps, if not , it means that the system time has not jumped. 3. The timestamp generating method of the real-time transport protocol system according to claim 3, wherein the preset value is 2S. 4. The timestamp generating method of the real-time transport protocol system according to any one of claims 1-3, further comprising: Obtain the time difference D ₀ between the time value of the zeroth data frame and the preset time, and use D ₀ as the time output value of the zeroth data frame. 5. A timestamp generation device for a real-time transport protocol system, characterized in that it comprises: An acquisition unit, configured to acquire the time value of the current data frame and the time value of the previous data frame of the current data frame; The first difference calculation unit is used to calculate the first difference D _i between the time value of the current data frame and the preset time, and the time value and the preset time of the previous data frame of the current data frame. The second difference D _i-1 ; An absolute value judging unit, configured to judge whether the system time jumps according to the absolute value |D _i -D _i-1 | of the difference between the first difference and the second difference; The first time output value calculation unit is used to use D _i -D _i-1 as the first backup difference Delta when the judgment result of the absolute value judgment unit is No, and use the first backup difference Delta Add the time output value Out _i-1 of the previous data frame to obtain the time output value Out _i of the current data frame; The time value unit is used to obtain the previous data frame of the previous data frame as the third data frame when the judgment result of the absolute value judgment unit is yes, and respectively obtain the data frame of the previous data frame time value and the time value of the third data frame; The second difference calculation unit is used to calculate the second difference D _i-1 between the time value of the previous data frame of the current data frame and the preset time, and the time value and the time value of the third data frame. The third difference D _i-2 of the preset time; The second time output value calculation unit is used to use D _i-1- D _i-2 as the second backup difference Delta', and compare the second backup difference Delta' with the time output value Out _i of the previous data frame _-1 is added to obtain the time output value Out _i of the current data frame; A timestamp generating unit, configured to multiply the time output value Out _i of the current data frame by the sampling rate of the data to obtain the timestamp of the current data frame. 6. the time stamp generating device of the real-time transport protocol system as claimed in claim 5, is characterized in that, described absolute value judgment unit is specifically used for: Judging whether the absolute value |D _i -D _i-1 | of the difference between the first difference and the second difference is greater than a preset value, if yes, it means that the system time jumps, if not , it means that the system time has not jumped. 7. The timestamp generating device of the real-time transport protocol system according to claim 6, wherein the preset value is 2S. 8. The timestamp generation device of the real-time transport protocol system according to any one of claims 5-7, further comprising: The initial acquisition unit is configured to acquire the time difference D ₀ between the time value of the zeroth data frame and the preset time, and use D ₀ as the time output value of the zeroth data frame.