KR101547697B1 - Device and method for synchronizing signal in mobile broadcasting receiver - Google Patents

Abstract

The present invention relates to an apparatus and a method for synchronizing a signal of a mobile broadcast receiver, and more particularly, to an apparatus and method for synchronizing a signal of a mobile broadcast receiver, the apparatus comprising a demultiplexer for demultiplexing a video timestamp and an audio timestamp using an IBT value, a video RBT value, And synchronizes the calculated video time stamp with a system time clock converted to the same frequency as the video time stamp to synchronize the calculated time stamp with the system time clock, To synchronize with the device.

Mobile broadcast receiver, synchronization, system time clock, video frame, audio frame

Description

TECHNICAL FIELD [0001] The present invention relates to a device for synchronizing a signal of a mobile broadcast receiver,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and method for synchronizing a signal of a mobile broadcast receiver for reproducing audio and video signals in a mobile broadcast receiver.

CMMB (China Multimedia Mobile Broadcasting) service, which is a Chinese mobile broadcasting standard, is a broadcasting service for a mobile terminal which can enjoy a TV program of a ground broadcasting such as mobile broadcasting of other countries at any time, even if commuting, .

CMMB broadcasting is a broadcasting service capable of serving video, audio, and data, and it is possible to manufacture a broadcasting receiver in a small size and power consumption can be greatly reduced. Of course, the amount of information that can be transmitted is small in comparison with the service of the fixed broadcast receiver, but it is sufficient for viewing with a mobile broadcast receiver.

The CMMB standard has various types according to flags, but currently implements video broadcasting in the H.264 / AVC standard and audio broadcasting in the MPEG-2 AAC standard. Also, ESG service is possible by linking data broadcasting.

In such a mobile broadcast, since video and audio data are transmitted separately and time is required for decoding, a lip-sync control method for outputting video and audio simultaneously is needed.

If the system time clock (STC) of the mobile broadcast receiver is equal to the reference time of the time stamp of the broadcast signal, the audio and video signals may be lip-synced using various known methods, When the system time clock of the broadcast signal is different from the reference time of the time stamp of the broadcast signal, an algorithm for lip-syncing the audio and video by matching the reference time and the system time clock with respect to the time stamp of the broadcast signal is required.

For example, in order to reproduce a CMMB service using a reference time of 22.5 KHz for a time stamp of an audio / video signal in a mobile broadcasting system using a STC (System Time Clock) at 90 KHz, An algorithm that lip-syncs the audio and video signals by matching the reference time for the audio / video signal of the audio / video signal is essential.

The present invention relates to a mobile broadcast receiver capable of synchronizing audio and video signals with a system time clock even when the reference time of a system time clock (STC) and a time stamp of a received broadcast signal are different from each other in a mobile broadcast receiver such as a DMB And a method thereof.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not intended to limit the invention to the particular embodiments that are described. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, There will be.

According to an aspect of the present invention, there is provided a method for decoding a video RBT (first broadcast time) value by parsing a header of an input multiple sub-frame to obtain an initial broadcast time (IBT) A Relative Broadcast Time (RBT) value and an audio RBT value; And calculating a video time stamp and an audio time stamp using the IBT value, the video RBT value, the IBT value, and the audio RBT value transmitted from the demultiplexer, respectively, and comparing the calculated video time stamp and the video time stamp And synchronizes the calculated audio time stamp with a system time clock converted into a frequency, and converts the calculated audio time stamp into a frequency equal to the system time clock and compares the calculated audio time stamp with a corresponding system time clock to synchronize.

Specifically, the synchronization control unit calculates a video time stamp using the IBT value and the video RBT value transmitted from the demultiplexing unit, and outputs the system time clock converted to the same frequency as the video time stamp, A video synchronization unit for comparing the time stamps to synchronize the video time stamps with the system time clock; And an audio time stamp calculating unit for calculating an audio time stamp using the IBT value and the audio RBT value transmitted from the demultiplexing unit, converting the calculated audio time stamp to the same frequency as the system time clock, And an audio synchronization unit for comparing the audio time stamps with each other to synchronize the audio time stamps with the system time clock.

Wherein the IBT is a reference time generated in a predetermined period and the RBT is offset relative to the IBT. The reference time frequency for the IBT and the RBT included in the multiple sub- And the frequency of the system time clock is different. The reference time frequency for the IBT and the RBT is 22.5 KHz, and the frequency of the system time clock is 90 KHz.

The system time clock, which is compared with the video time stamp, is calculated by adding the IBT initial value stored after the IBT value is converted to the same frequency as the system time clock and the instantaneous value of reading the system time clock, As shown in FIG.

According to an aspect of the present invention, there is provided a method for obtaining an initial IBT (Initial Broadcast Time) value from received multiple subframes and converting the obtained IBT value to the same frequency as a system time clock. Storing the frequency-converted IBT value as an initial value and initializing a system time clock; Parsing a video section from the received multiple subframes to obtain a video relative temporal time (RBT) value, and calculating a video timestamp using the obtained RBT value and the first IBT value; And adjusting output of the video signal by converting the system time clock to the same frequency as the IBT and comparing the video time stamp based on the frequency converted system time clock.

In particular, when converting the system time clock to the same frequency as the IBT, the frequency of the mobile broadcast receiver is converted by adding the instantaneous value of the system time clock and the stored IBT initial value.

According to still another aspect of the present invention, there is provided a method for receiving an initial broadcast time (IBT) value from a received multiple subframe, storing the initial IBT value as an initial value, and initializing a system time clock; Parsing an audio section from the received multiple subframes to obtain an audio RBT value, calculating an audio time stamp using the obtained RBT value and the IBT initial value; And controlling the output of the audio signal by converting the calculated audio time stamp to a frequency equal to the system time clock and comparing the frequency timed audio time stamp based on the system time clock.

As described above, according to the present invention, audio and video signals can be reproduced according to a predetermined algorithm even when the system time clock (STC) of the mobile broadcast receiver and the reference time for the time stamp of the received broadcast signal are different from each other Therefore, it is unnecessary to redesign the STC system that coincides with the reference time of the broadcast signal, and the existing STC system can be used, and the cost of redesigning can be reduced.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a functional block diagram illustrating a mobile broadcast receiver for synchronizing broadcast signals according to an embodiment of the present invention. The mobile broadcast receiver 100 includes a demodulator 110, a reception buffer 115, a demultiplexer A synchronization processor 130, a video decoder 140, a video processor 145, and an audio decoder 160.

For convenience of explanation, in the embodiment, when the system time clock (STC) of the mobile broadcast receiver 100 uses 90 KHz as in a mobile broadcasting system such as Korea and Japan, and when the time stamp (Time (CMMB) is used as an example, the present invention is not limited to this, and it is applicable to all cases in which the reference time of the system time clock and the broadcast signal are different from each other It is natural to be able to.

The demodulator 110 processes the mobile broadcast signal received through the antenna and outputs a TS packet, and the reception buffer 115 temporarily stores the TS packet.

The demultiplexer 120 is configured to identify the type of data included in the TS packet by referring to the header information of the received TS packet, and to generate audio and video frames. That is, the demultiplexer 120 demultiplexes multiplexed audio and video bit streams when an audio / video multiplex sub-frame (MSF) is input. The separated audio bitstream and video bitstream are output to the video decoder 140 and the audio decoder 160, respectively, for decoding.

The demultiplexer 120 parses the multiple subframes (MSF) through the stream parser 125 to obtain the initial broadcast time (IBT) value, and parses the respective video and audio bitstreams (RBT) value and an audio RBT value, which are time information, to the synchronization controller 130 for synchronization between the video / audio frame and the system time clock.

The multiplex sub-frame (MSF) input to the demultiplexer 120 is configured as shown in FIG. That is, the multiple subframes include a sub-frame header, a video section, an audio section, and a data section.

As shown in FIG. 2, the initial broadcast time (IBT) is multiplexed in the headers of the multiple subframes. In the video and audio sections of the multiple subframes (MSF), each header Relative Broadcast Time (RBT), which is relative broadcast time information, is multiplexed in the Video section header and Audio section header, respectively.

The IBT corresponds to time information such as a PCR (Program Clock Reference) of MPEG-2 with a reference time generated every predetermined period as shown in FIG. 4, and the RBT is offset relative to the IBT to be. A plurality of RBT values RBT0 to RBT24 may be allocated between the IBT values IBT0, IBT1, ... generated every predetermined period.

The synchronization controller 130 calculates a video time stamp and an audio time stamp using the IBT value, the video RBT value, the IBT value, and the audio RBT value, which are time information transmitted from the demultiplexer 120, Synchronized with the system time clock converted to the same frequency as the video time stamp, and converts the calculated audio time stamp into the same frequency as the system time clock, . That is, the synchronization control unit 130 adjusts the output time of the video and audio frames by synchronizing the calculated video time stamp and the audio time stamp with the frequency of the system time clock, respectively.

The synchronization unit 130 includes a video synchronizing unit 131 and an audio synchronizing unit 135. The video synchronizing unit 131 synchronizes the video and audio signals using the IBT value and the video RBT value transmitted from the demultiplexing unit 120. [ And to synchronize the video time stamp with the system time clock by comparing the calculated system time clock with the system time clock converted to the same frequency as the video time stamp and comparing the calculated video time stamp with each other. The audio synchronization unit 135 calculates an audio time stamp using the IBT value and the audio RBT value transmitted from the demultiplexing unit 120. The audio synchronization unit 135 converts the calculated audio time stamp into the same frequency as the system time clock, And compare the audio time stamp with the system time clock to synchronize the audio time stamp with the system time clock.

The system time clock, which is compared with the video time stamp in the video synchronization unit 131, is a value obtained by converting the IBT initial value, which is stored after the IBT value is converted to the same frequency as the system time clock, And is converted to the same frequency as the video time stamp.

In this way, the synchronization control unit 130 can obtain the video time stamp and the audio time stamp, respectively, and synchronize the output timing of the video and audio frames by comparing the video time stamp and the audio time stamp with the system time clock having the same frequency as each time stamp.

The video decoder 140 removes overhead (various kinds of header information, start code, etc.) from the inputted video bitstream, performs variable length decoding (VLD) on pure data information, and then performs an inverse quantization process and an inverse discrete cosine (IDCT), restores the pixel values of the original screen, and the video processor 145 converts the pixel values into the display format and outputs the converted values to the display unit 150. Here, the video processing unit 145 may compare the video time stamp output from the synchronization control unit 130 with the system time clock having the same frequency as the video time stamp to adjust the output timing of the video frame output to the display unit 150 have.

The audio decoder 160 restores the input audio bitstream to an original signal using an MPEG algorithm or an audio coding (AC-3) algorithm, and the digital-to-analog converter 165 (DAC) (170). Here, the audio decoder 160 may adjust the output timing of the audio frame output to the speaker 170 by comparing the audio time stamp output from the synchronization controller 130 with the system time clock.

Since the mobile broadcast receiver uses multiplexed digital signals, a separate A / V Lip-Synchronization device or method for synchronizing video and audio frames is required unlike the conventional analog system. In such a mobile broadcast receiver, an algorithm for synchronizing the system time clock with the reference time for the time stamp in an environment where the system time clock (STC) and the reference time for the time stamp of the received broadcast signal are different from each other is required.

Accordingly, the synchronization control unit 130 of the mobile broadcast receiver obtains the video time stamp and the audio time stamp using the IBT value, the video RBT value, and the audio RBT value provided from the demultiplexing unit 120, And the audio time stamp with a system time clock of the same frequency as each time stamp, respectively, to adjust the output time of the video and audio frames.

5 and 6 are flowcharts illustrating a synchronization process between a video and audio frame and a system time clock according to an embodiment of the present invention, respectively, and will be described with reference to the accompanying drawings.

The video frame and the audio frame may be sequentially synchronized with the system time clock (STC). However, in the embodiment of the present invention, the video frame and the audio frame are transmitted to the video synchronizer 131 of the synchronization controller 130, And the audio synchronizing unit 135 are simultaneously performed.

First, the stream parsing unit 125 of the demultiplexer 120 parses the header of the input multiple subframe (MSF), parses the header, and stores the value of the first IBT (for example, IBT0) (S11). Here, the IBT value is time information generated by a reference time having a frequency of 22.5 KHz.

The video synchronization unit 131 of the synchronization control unit 130 changes the IBT0 value transmitted from the demultiplexing unit 120 to 90 KHz which is the same frequency as the externally supplied system time clock, (S12). Since the frequency (90 KHz) of the system time clock is four times the frequency of the IBT value (22.5 KHz), the IBT value may be shifted by 4 bits, that is, the IBT value may be shifted to the left by two bits. For example, if the IBT0 value is 0x0001, shifting this value to the left by 2 bits results in 0x0100. Here, the IBT0 value becomes 0x0001, and the IBT0 value stored as the initial value becomes the frequency converted 0x0100.

Subsequently, the frequency of the IBT0 value is changed, and at the same time, the video synchronization unit 131 initializes the externally supplied system time clock to '0' (S13).

Converting the frequency of the IBT0 value, storing the frequency-converted IBT0 value as an initialization value, and initializing the system time clock supplied from the outside.

Meanwhile, the stream parsing unit 125 of the demultiplexer 120 parses and parses the header of the video section separated from the multiple subframes (MSF) and obtains the first video RBT (for example, RBT0) To the video synchronization unit 131 (S14). Here, the RBT value is time information generated by a reference time having a frequency of 22.5 KHz. The IBT is a reference time generated every predetermined period as shown in FIG. 4, and the RBT is relative time information offset from the IBT. A plurality of RBT values RBT0 to RBT24 may be allocated between the IBT values IBT0, IBT1, ... generated every predetermined period.

Then, the video synchronization unit 131 calculates and acquires a video time stamp using the RBT0 value and the IBT0 value transmitted from the demultiplexing unit 120 (S15). The method of obtaining the video time stamp is shown in Equation 1 below.

Equation (1) shows a case where 25 RBT values exist between IBT0 and IBT1, that is, 25 frames / sec.

As shown in Equation (1), the timestamp for a specific video access unit (V_AU) adds the corresponding IBT value and the corresponding RBT value. In case of the RBT value, since it is an offset value with respect to the IBT value, two values are added to the time stamp.

Then, the video synchronization unit 131 adds the read system time clock value and the stored IBT initial value at the moment of reading the system time clock for comparison with the calculated video time stamp, and sets the system time clock value to 22.5 KHz (S16). Here, the method of converting the frequency of the system time clock is a method of dividing the value of the system time clock by 4 because the frequency (90 KHz) of the system time clock is four times the frequency of the IBT value (22.5 KHz) Value to the right by two bits. For example, if the value of the system time clock is 0x1000, shifting this value to the right by 2 bits results in 0x0010.

The video synchronization unit 131 compares the system time clock (STC) converted to 22.5 KHz and the calculated video time stamp (22.5 KHz) as described above so that the video frame can be synchronized with the system time clock. Accordingly, the video frame output to the display means 150 through the video decoder 140 and the video processor 145 may be delayed for a predetermined time by synchronization with the system time clock (S17).

The video synchronizer 131 checks video timestamps based on the system time clock (STC), and controls the video decoder 140 and the video processor 145 such that the video frames are synchronized with the system time clock. The video synchronization unit 131 transfers the calculated video time stamp to the video processing unit 145 and the video processing unit 145 outputs the video time stamp output from the video synchronization unit 131 to the same frequency as the video time stamp The output timing of the video frame output to the display means 150 may be adjusted.

6, the audio synchronization unit 135 of the synchronization control unit 130 receives the IBT (e.g., IBT0) value parsed through the multiple subframes (MSF) from the demultiplexing unit 120, The transmitted IBT0 value is stored as an initial value (S21), and the externally supplied system time clock is initialized to '0' (S22).

At this time, the IBT value is also transmitted to the video synchronizing unit 131, and the audio synchronizing unit 135 and the video synchronizing unit 131 receive the same IBT value from the demultiplexing unit 120.

The process of storing the IBT0 value as an initialization value and the process of initializing an externally supplied system time clock are simultaneously performed.

Meanwhile, the stream parsing unit 125 of the demultiplexer 120 parses the header of the audio section separated from the multiple subframes (MSF), parses the first audio RBT (for example, RBT0) obtained by parsing To the audio synchronizing unit 135 (S23). Here, the RBT value is time information generated by a reference time having a frequency of 22.5 KHz. The IBT is a reference time generated every predetermined period as shown in FIG. 4, and the RBT is relative time information offset from the IBT. A plurality of RBT values RBT0 to RBT24 may be allocated between the IBT values IBT0, IBT1, ... generated every predetermined period.

Next, the audio synchronizer 135 calculates and acquires an audio time stamp using the RBT0 value transmitted from the demultiplexer 120 and the IBT0 initial value stored at step S24. The method of obtaining the audio time stamp is shown in Equation 2 below.

Equation (2) shows a case where 25 RBT values exist between IBT0 and IBT1, that is, 25 frames / sec, and First IBT has the same value as the IBT0 value.

As shown in Equation 2, the timestamp for a specific audio access unit A_AU is obtained by adding the corresponding IBT value and the corresponding RBT value, and subtracting the IBT value (for example, IBT0) stored as an initial value. Since the time stamps for A_AU0 to A_AU24 in Equation (2) are equal to the IBT0 value and the First IBT, each RBT value will be a time stamp, and the time stamp for A_AU25 is a value obtained by subtracting the First IBT value from the IBT1 value and the RBT0 value The added value will be the timestamp for the audio access unit A_AU25.

Next, the audio synchronizing unit 135 converts the calculated audio time stamp to 90 KHz, which is equal to the system time clock (S25). Here, the method of converting the frequency of the audio time stamp is a method of multiplying the value of the audio time stamp by 4, that is, the audio time stamp is multiplied by 4 because the reference frequency (22.5 KHz) of the audio time stamp is 1/4 of the system time clock (90 KHz) The value of the stamp may be shifted to the left by two bits. For example, if the value of the audio timestamp is 0x0010, shifting this value to the left by 2 bits results in 0x1000.

The audio synchronizer 135 compares the audio time stamp converted to 90 KHz and the system time clock as described above so that the audio frame can be synchronized with the system time clock. Accordingly, the audio frame output to the speaker 170 through the audio decoder 160 and the digital-to-analog converter 165 may be delayed for a predetermined time by synchronizing with the system time clock (S26).

The audio synchronizer 135 checks the audio time stamp based on the system time clock (STC) and controls the audio decoder 160 to synchronize the audio frame with the system time clock. However, the audio synchronizer 135 Transmits the calculated audio time stamp to the audio decoder 160 and compares the audio time stamp output from the audio synchronization unit 135 in the audio decoder 160 with the system time clock having the same frequency as the audio time stamp The output timing of the audio frame output to the speaker 170 side through the DAC 165 may be adjusted.

Since the audio frame and the video frame are synchronized with respect to the same system time clock, synchronization between the video frame and the audio frame also occurs. That is, the video timestamp and the audio timestamp are checked and synchronized with each other based on the system time clock, so that synchronization between the video frame and the audio frame is not required.

In the case of the video time stamp, it is effective to convert the frequency of the system time clock to match the frequency of the video time stamp. In case of the audio time stamp, the frequency of the audio time stamp is converted to match the system time clock It is efficient.

It will be apparent to those skilled in the relevant art that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. The appended claims should be construed in accordance with the appended claims and their equivalents.

1 is a functional block diagram illustrating a mobile broadcast receiver for synchronizing broadcast signals according to an embodiment of the present invention.

2 is a diagram illustrating the structure of multiple subframes of a broadcast signal applied to the present invention.

FIGS. 3A and 3B are views showing detailed configurations of a video section and an audio section of multiple subframes applied to the present invention, respectively.

4 is a diagram showing a relationship between an IBT and an RBT applied to the present invention.

5 is a flowchart illustrating a synchronization process of a video frame according to an embodiment of the present invention.

6 is a flowchart illustrating a synchronization process of an audio frame according to an embodiment of the present invention.

DESCRIPTION OF THE REFERENCE NUMERALS

100: mobile broadcast receiver 120: demultiplexer (demultiplexer)

121: Stream parsing unit 130:

131: video synchronization unit 135: audio synchronization unit

140: video decoder 145: video processor

160: Audio decoder

Claims (10)

A demultiplexer for parsing input multiple subframes to obtain video and audio related time information; A video time stamp set in accordance with the mobile broadcast service using the video related time information input from the demultiplexer, and a system time clock converted to the same frequency as the video time stamp and the calculated video time stamp A video synchronizer for comparing the video timestamps with each other to synchronize the video timestamps with the system time clock; And A demultiplexer for demultiplexing the audio time stamp into a plurality of audio time stamps, an audio time stamp preset according to the mobile broadcast service using the audio time information input from the demultiplexer, And an audio synchronization unit for comparing the time stamp and the system time clock before conversion to synchronize the audio time stamp with the system time clock, Wherein the video synchronization unit calculates the video time stamp using an initial broadcast time (IBT) value and a video relative broadcast time (RBT) value included in the input multiple subframe, Wherein the audio synchronization unit calculates the audio time stamp using an IBT value and an audio RBT value included in the input multiple subframe. delete The method according to claim 1, Wherein the IBT is a reference time generated every predetermined period and the RBT is offset relative to the IBT. The method according to claim 1, Wherein the frequency of the system time clock is a power of 2 of a reference time frequency for IBT and RBT included in the multiple subframe. 5. The method of claim 4, Wherein the reference time frequency for the IBT and the RBT is 22.5 KHz, and the frequency of the system time clock is 90 KHz. Obtaining an initial IBT (Initial Broadcast Time) value from the received multiple subframes, and converting the obtained IBT value to the same frequency as the system time clock; Storing the frequency-converted IBT value as an initial value and initializing a system time clock; Parsing a video section from the received multiple subframes to obtain a video relative temporal time (RBT) value, and calculating a video timestamp using the obtained RBT value and the first IBT value; And Transforming the initialized system time clock to the same frequency as the IBT, and adjusting the output of the video signal by comparing the frequency-converted system time clock with the calculated video time stamp. The method according to claim 6, And when converting the system time clock to the same frequency as the IBT, adding the instantaneous value of the system time clock reading and the stored IBT initial value to convert the frequency. The method according to claim 6, Wherein the video time stamp is calculated according to Equation (1) below. Equation 1

Here, V_AU is a specific video access unit. Acquiring an initial IBT (Initial Broadcast Time) value from the received multiple subframes, storing the initial IBT value as an initial value, and initializing a system time clock; Parsing an audio section from the received multiple subframes to obtain an audio RBT value, calculating an audio time stamp using the obtained RBT value and the IBT initial value; And Converting the calculated audio time stamp to a frequency equal to the system time clock, and adjusting the output of the audio signal by comparing the system time clock and the frequency-converted audio time stamp. 10. The method of claim 9, Wherein the audio time stamp is calculated by the following equation (2). Equation 2

Here, A_AU is a specific audio access unit, and First IBT is the same value as IBT0.

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