KR100915798B1 - Method for recording digital broadcasting by enhanced compressing format - Google Patents

Abstract

The present invention relates to a digital broadcast recording technique using an improved compression format. In particular, the present invention improves the PTS value of TS data contained in a digital broadcast signal so that different types of data such as video data and audio data can be synchronized. The present invention relates to a digital broadcast recording technology capable of implementing various functions in addition to a simple playback function by storing digital broadcast data in a compressed format. According to the present invention, even if the PTS value of the received TS data shows an irregular distribution, the video data and the audio data can be synchronized, and the total reproduction time of the digital broadcast data can be accurately calculated. In addition, it is possible to easily implement a function such as fast forward, rewind, and double speed playback, which are difficult to implement with TS data alone.

Digital Broadcasting, DMB, Mobile Broadcasting, PTS, Synchronization, Recording

Description

Method for recording digital broadcasting by enhanced compressing format

The present invention relates to a digital broadcast recording technique using an improved compression format. In particular, the present invention improves the PTS value of TS data contained in a digital broadcast signal so that different types of data such as video data and audio data can be synchronized. The present invention relates to a digital broadcast recording technology capable of implementing various functions in addition to a simple playback function by storing digital broadcast data in a compressed format.

Digital broadcasting collects broadcast contents of several channels, separates them into audio data and video data, encodes them into a predetermined compressed format, and then separates them into units of 188 bytes to generate TS data. The TS data is loaded on a digital broadcast signal and transmitted to the receiver through a terrestrial wave, satellite, or cable.

Recently, a digital transmission technology capable of receiving digital broadcasting through a mobile terminal has been developed, and a portable digital broadcasting terminal capable of receiving DMB broadcasting in combination with a mobile phone has been released.

When a digital broadcast is first received, it is stored in the form of TS data, but TS data itself is not easy to implement functions other than the simple play and stop function. That is, since the PTS value included in the TS data is a value that increases in a limited bit space, it is not always an increase value, and may sometimes increase or decrease irregularly. There is a problem that can not accurately grasp.

In addition, since it is not easy to implement a special playback function such as fast forwarding or rewinding because the exact playback time of each frame of digital broadcast data cannot be determined for the above reason, it is inconvenient to record and immediately play a digital broadcast from the user's point of view. There is a problem that may result.

Therefore, in order to permanently store digital broadcast data, it is desirable to generate and store a file encoded in a more compressed format. However, encoding digital data in a general compression format is not only time consuming, but also requires complicated computational processes, and is a limitation of many hardware resources in encoding digital broadcasting through a mobile digital broadcasting terminal rather than a general digital television. There is a problem that may result.

An object of the present invention is to synchronize the video data and audio data included in the digital broadcast signal, and digital broadcast recording that can implement functions such as FF (fast forward) & REW (rewind) of a high-compression format general video, which is difficult to realize only by TS data. To provide technology.

A digital broadcast recording method according to an improved compression format according to the present invention includes the steps of: (a) receiving a digital broadcast signal mixed with a plurality of types of packet data; (b) dividing the digital broadcast signal by the type of packet data and sequentially reading the frames in order of frames when a recording control signal is generated; (c) extracting a PTS value stored for each frame in a plurality of types of packet data; (d) generating a cumulative PTS value for the current frame in each of the plurality of types of packet data, and allocating the generated cumulative PTS value for each frame to generate digital broadcast data according to a preset compression format; And (e) storing the generated digital broadcast data.

According to the present invention, even if the PTS value of the received TS data shows an irregular distribution, the video data and the audio data can be synchronized, and the total reproduction time of the digital broadcast data can be accurately calculated.

In addition, it is possible to easily implement a function such as fast forward, rewind, and double speed playback, which are difficult to implement with TS data alone.

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

1 is a diagram showing the overall system configuration of a digital broadcasting system for receiving a digital broadcasting signal transmitted from a broadcasting station through a digital broadcasting terminal.

In addition to terrestrial television broadcasts such as ATSC and DVB-T, digital broadcasting includes mobile digital multimedia broadcasting technology developed for mobile environments such as DMB and ISDB-T. Here, the DMB service will be described.

In the case of terrestrial DMB, the broadcast station 10 encodes broadcast content for each channel in a specific compression format to generate packet data including video data and audio data.

In addition, the broadcasting station 10 loads packet data including broadcast contents through a broadcast network 20 in a digital broadcast signal and transmits the data through each medium.

For example, when the digital broadcast signal is transmitted on the carrier frequency through the repeater 30, the digital broadcast terminal 40 receives the digital broadcast signal, extracts packet data from the digital broadcast signal, and separates the video data and the audio data. Decodes and reproduces the signal that can be output to the screen and speakers.

In the case of satellite DMB, the broadcasting station 10 launches various contents of various channels to the satellite 50 through the Ku band frequency, and the satellite 50 broadcasts the terrestrial digital broadcasting through the S-band frequency allocated for the DMB. By spraying to the terminal 40, digital broadcast transmission is performed.

2 is a flowchart showing the overall operation of the digital broadcast recording method according to the improved compression format according to the present invention.

First, a digital broadcast terminal receives a digital broadcast signal mixed with a plurality of types of packet data, and separates the digital broadcast signal for each type of packet data (ST10). In this case, the plurality of types of packet data generally mean video data and audio data, but may be referred to as 'A data' and 'B data' because they may be applied to other data other than video and audio data. In addition, the present invention can be applied not only to two kinds of data but also to three or more kinds of multi-packet data. 2, 3 and 4 will be described taking the case of video data and audio data as an example.

After receiving the digital broadcast signal, when the recording control signal is generated due to an operation such as pressing a recording button by the user of the digital broadcasting terminal (ST20), the video data and the audio data separated according to the type of packet data are sequentially ordered in the frame order. Read (ST30).

Video data and audio data reconstructed from a digital broadcast signal constitute a screen and audio signal in units of frames, and contain 30 to 60 frames per second. The screen configured by the MPEG format is composed of three frames of I, B, and P. However, when limited to DMB broadcasting, the screen is composed of only two frames of I, P. Therefore, it can be said that frames are sequentially arranged in video data.

After reading the video data and the audio data, PTS values stored for each frame are extracted (ST40).

In the video data and audio data generated in the MPEG format by the broadcasting station, a presentation time stamp (PTS) value is stored in units of frames, and the PTS value is a value representing a playback time of the current frame. However, since the bit size representing the PTS value is limited, when the PTS value increases above the maximum value, the numerical value that can be represented by the limited bit is repeatedly increased. Therefore, the absolute playback time cannot be determined only by the PTS value, but other data must be referred to. Therefore, in the subsequent process, the information to know the absolute playback time of each frame is generated using the extracted PTS value.

That is, in each of the video data and the audio data, a cumulative PTS value for the current frame is generated, and the generated cumulative PTS value is allocated to each frame of the video data and the audio data to generate digital broadcast data according to a preset compression format. (ST50) The cumulative PTS value is a processing of the original PTS value after securing the size of the data space so that it can continue to increase even if the stored PTS value for each frame of the digital data increases above the maximum value. Set the size of the data space so that it doesn't happen. A more detailed calculation process of the cumulative PTS value will be described in more detail with reference to FIG. 3.

Then, digital broadcast data of a specific compression format generated in the digital broadcast terminal is stored (ST60). In this case, the generated specific compression format is a compression format in which a previously generated cumulative PTS value is stored for each frame of digital broadcast data, and can be presented in various ways. In the present invention, the RIFF format whose extension is represented by AVI The present invention provides a method of generating digital broadcast data capable of storing a cumulative PTS value.

The resource iinterchange file format (RIFF) format is a format for converting and modifying video, audio, and images between files. The AVI (audio / video interlaced file format) file format was first introduced by Microsoft in 1992. It is a multimedia compression format.

AVI files are basically composed of chunks, and all AVI files consist of a parent chunk named RIFF 'AVI', and three child chunks: List 'hdrl', List 'movi', and index. Each child chunk contains a plurality of chunks having detailed information.

Among these, the index chunk has four values of a chunk identifier, a flag, an offset, and a length. In the present invention, the cumulative PTS value is stored using a flag region of the index chunk. .

In the original RIFF format, the flag area of the induct chunk stores information for identifying whether the current frame is an I-frame. Here, the I-frame means a frame that is first referenced to recover another frame.

Therefore, after storing the cumulative PTS value in the flag area of the index chunk, the I-frame presence information originally stored in the flag area of the index chunk must be stored in another area. In the present invention, some bits of the length region of the index chunk are used to store I frame presence information of the current frame. For example, it is set to indicate whether or not an I frame according to whether the upper bit of the length area is 1 or 0. Even if the data already stored in the length area is a large value, both information can be stored without affecting the corresponding bit.

Through the above process, the process of generating and storing digital broadcast data of a specific compression format including a cumulative PTS value from the digital broadcast signal received after the recording command generation is repeated until the recording end command is generated (ST70). However, if the recording command does not occur, there is no need to generate and store digital broadcast data, so only the operation of decoding and playing the received digital broadcast signal in real time is performed (ST80).

FIG. 3 is a flowchart illustrating an operation process of generating digital broadcast data including a cumulative PTS value in FIG. 2 (ST50) in more detail.

First, in each of the video data and the audio data, the difference between the PTS value of the current frame of each data and the PTS value of the previous frame (hereinafter referred to as a 'PTS interval') is calculated (ST51), and the PTS of the calculated current frame is calculated. While the interval represents a normal value that does not deviate from the preset first reference range (ST52), the cumulative PTS value is calculated by accumulating the PTS interval in each frame unit and stored in the current frame (ST57). For example, if the PTS interval indicates a value between 0 and 5 seconds, it is determined that the PTS value is normal.

That is, if the PTS value of the previous frame is 1000 and the PTS value of the current frame is 1030, since 1030-1000 = 30, the PTS interval based on the current frame is 30. If the PTS value can be expressed from 0 to 999, it may increase to 930, 960, and 990, but not to 1020, but may lead to 20, 50, etc. The calculated cumulative PTS value continues to increase.

At this time, if the PTS interval of either the video data or the audio data is out of the first reference range (ST52), it is determined that the data transmission is not normal, so instead of calculating the cumulative PTS value through the PTS interval, the average value of the PTS intervals is calculated. Apply to calculate the cumulative PTS value. If the PTS interval of the video data shows a difference of 5 seconds or more, it is determined to be an abnormal situation.

That is, the average value of the PTS intervals is calculated by obtaining the average change value of the PTS values between the frames of the data (ST53), and the cumulative PTS value is calculated by adding the average value of the PTS intervals of the data to the cumulative PTS value of the previous frame of the data. To store in the current frame (ST54).

However, if the PTS interval of either the video data or the audio data is out of the first reference range, but the difference between the PTS value of the video data and the PTS value of the audio data based on the current frame does not exceed the preset second reference range (ST55). ), It is determined that the PTS values of the video data and the audio data are outside the allowable range, and then the two PTS values are returned within the allowable range as one PTS value is changed irregularly. For example, the case where the PTS interval of video data shows a difference of 5 seconds or more, but the difference in PTS value with audio data shows less than 3 seconds can be considered.

In this case, since the reference values of the two types of data may be different, it is necessary to synchronize the video data and the audio data. Accordingly, the video data and the audio data are synchronized by correcting the cumulative PTS value of the video data according to the cumulative PTS value of the audio data (ST56).

FIG. 4 is a flowchart illustrating an additional step of reproducing digital broadcast data and implementing trick play such as FF / REW in addition to the overall operation of FIG. 2.

When generating and storing digital broadcast data by the compression format proposed by the present invention, information necessary for reproducing the digital broadcast data must be generated later.

To this end, a sequence parameter set (SPS) and a picture parameter set (PPS) are extracted from the digital broadcast signal and added to the front of the video region of the digital broadcast data, and audio decoder specification information is extracted from the digital broadcast signal to extract audio from the digital broadcast data. The digital broadcast data is generated by adding it to the front of the area (ST90).

Here, SPS and PPS are information required to initialize the video decoder for video playback, and audio decoder specification information is information necessary to initialize the audio decoder for audio playback. The method of storing decoding information by using SPS, PPS, and audio decoder specification information is applied to T-DMB, and in case of digital broadcasting such as ISDB-T and DVB-T, additional information necessary for decoding through other methods is used. It can also be implemented to store.

After the digital broadcast data is generated and stored, if a playback command is generated by an operation such as a user's play button operation, the digital broadcast data recorded through the above process is decoded and reproduced (ST100).

At this time, if an FF / REW control signal is generated according to an external user control signal such as a user's key operation (ST110), the playback time of each frame is calculated using the cumulative PTS value stored for each frame of digital broadcast data, and the FF / REW, etc. The playback position of the digital broadcast data is shifted in correspondence with the control signal of step S120. That is, by referring to the accumulated PTS value stored in the flag chunk area of the index chunk in the RIFF format, it is possible to confirm the absolute reproduction time of the digital broadcast data, thereby facilitating the implementation of trick play operations such as FF and REW.

5 is an exemplary diagram listing situations in which the PTS value included in the digital broadcast signal is changed irregularly.

3 illustrates a case in which the PTS values of the video data and the audio data are outside the allowable ranges, and then two PTS values are returned within the allowable ranges while one PTS value is irregularly changed. Instead of the data, A data and B data are represented.

In the four cases described below, this is also the case when the expression is collectively changed by decreasing instead of increasing or decreasing the PTS value.

■ CASE 1: The PTS value of A data is increased and it is different from the PTS value of B data. Then, the PTS value of B data is increased, and the difference between PTS values between two data becomes constant again.

■ CASE 2: The PTS value of A data is increased and the PTS value of B data is decreased, so the difference of PTS value between two data is greatly widened. Then, the PTS value of the A data was greatly reduced, so that the difference between the PTS values of the two data became constant again.

■ CASE 3: The PTS value of A data increases and the difference of PTS value increases. The PTS value of B data decreases, so the difference of PTS value between two data increases. Then, the PTS value of the A data decreased and the PTS value of the B data increased, so that the difference between the PTS values of the two data became constant again.

■ CASE 4: The PTS value of A data is increased and the difference of PTS value between two data increases. Then, the PTS value of A data is decreased again, and the difference of PTS value between two data becomes constant again.

6 is a flowchart illustrating an actual implementation of an algorithm for accumulating PTS values.

When recording starts, the current PTS value (CurPTS) of the reference data (eg, video data) is read.

The cumulative PTS value is defined as TotalPTS = ResyncPTS + (CurPTS-StartPTS). At the time of recording, the ResyncPTS value is initialized to zero. StartPTS is set to the current PTS value. For example, if the PTS values increase to 1030, 1060, 1090 ..., the cumulative PTS values become 30, 60, 90.

Next, if the previous PTS value (PrevPTS) is greater than the current PTS value or the current PTS value is more than 5 seconds different from the previous PTS value, it is determined that the PTS value is abnormally increased and the current cumulative PTS value (CurTotalPTS) is determined. The cumulative PTS value PrevTotalPTS is calculated by adding the average value AvgIncPTS of the PTS interval to. To do this, reset the StartPTS to the PTS value of the current frame and store the accumulated PTS value in ResyncPTS. That is, by setting StartPTS = CurPTS and ResyncPTS = TotalPTS + AvgIncPTS, a normal cumulative PTS value is calculated.

However, if the PTS value shows a normal increase, the current cumulative PTS value (CurTotalPTS) is added to the previous cumulative PTS value (PrevTotlaPTS) by adding a PTS interval (DiffPTS) defined as a difference between the current PTS value and the previous PTS value. Calculate. Then, the current PTS value is set to the previous PTS value for the next step.

In the case where the PTS value is abnormally increased, the difference between the PTS value of other types of data (for example, audio data) is 3 even though the difference of the PTS value of the current reference data is more than 5 seconds or less than 0. If it is within the second, it is necessary to synchronize the two data by determining that the difference between the PTS values of the two data is out of the allowable range and then back into the allowable range. Under normal circumstances, in order to synchronize the two data, the PTS value of the two data should be increased within the allowable range.

If the PTS value is changed irregularly, since the initially set ResyncPTS and StartPTS are different from each other, it is not possible to be sure that the accumulated PTS values of the two data are synchronized with each other at this time.

For example, in the case of video data and audio data,

VideoResyncPTS = 2000, VideoStartPTS = 10030

AudioResyncPTS = 2050, AudioStartPTS = 10060

Consider the case of.

In this case, since the ResynaPTS value of the audio data is larger than that of the video data, the cumulative PTS value is also increased by 50. However, since the StartPTS value of the audio data is larger than that of the video data but is negative, the cumulative PTS value is reduced by 30. As a result, the cumulative PTS value of the audio data has a value 20 larger than that of the video data.

Thus, by adding 20 to ResyncPTS of video data or subtracting 20 from ResyncPTS of audio data, synchronization of the two data can be achieved. In this case, when the current value of ResyncPTS is decreased, the cumulative PTS value may not increase continuously. Therefore, it is preferable to add 20 to ResyncPTS of video data to synchronize the two data instead of subtracting the value of audio data. .

Although the present invention has been described in more detail with reference to the examples, the present invention is not necessarily limited to these embodiments, and various modifications can be made without departing from the spirit of the present invention. Therefore, the embodiments disclosed in the present invention are not intended to limit the technical idea of the present invention but to describe the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The protection scope of the present invention should be interpreted by the following claims, and all technical ideas within the equivalent scope should be interpreted as being included in the scope of the present invention.

1 is a diagram showing the overall system configuration of a digital broadcasting system for receiving a digital broadcasting signal transmitted from a broadcasting station through a digital broadcasting terminal;

2 is a flow chart showing the overall operation of the digital broadcast recording method according to the improved compression format according to the present invention;

FIG. 3 is a flowchart illustrating an operation process of generating digital broadcast data including a cumulative PTS value in FIG. 2 (ST50) in more detail.

FIG. 4 is a flowchart illustrating a process of adding digital play data reproduction steps and trick play implementation steps such as FF / REW added to the overall operation of FIG.

5 is an exemplary diagram listing situations in which a PTS value included in a digital broadcast signal is changed irregularly;

6 is a flowchart illustrating an actual implementation of an algorithm for accumulating PTS values.

Claims (7)

delete (a) receiving a digital broadcast signal mixed with a plurality of types of packet data; (b) dividing the digital broadcast signal by packet data and sequentially reading the digital broadcast signal in frame order when a recording control signal is generated; (c) extracting PTS values stored for each frame in the plurality of types of packet data; (d) (d-1) In each of the plurality of types of packet data, the first difference between the PTS value of the current frame and the PTS value of the previous frame (hereinafter, referred to as a 'PTS interval') of each data is set in advance. The value calculated by accumulating the PTS interval in each frame unit while not departing from the reference range is stored in the current frame as a cumulative PTS value for the current frame, and (d-2) the plurality of types in step (d-1). If the PTS interval of any one of the packet data is out of the first reference range, the PTS interval average value of the corresponding data is added to the cumulative PTS value of the previous frame of the data as the cumulative PTS value for the current frame. (D-3) the PTS interval of any one of the plurality of types of packet data is out of the first reference range in step (d-2), but is based on the current frame. If the difference between the PTS values between the data does not deviate from the preset second reference range, the cumulative PTS value of each of the plurality of types of packet data is corrected according to the cumulative PTS value of any one of the plurality of types of packet data. Synchronizing packet data of (d-4) and generating the packet data into digital broadcast data according to a preset compression format; And (e) storing the generated digital broadcast data; Digital broadcast recording method comprising a. The method according to claim 2, In the step (b), the video data is separated and extracted as the A data from the plurality of types of packet data (hereinafter referred to as 'A data' and 'B data'), and the audio data signal is separately extracted as the B data. And dividing the digital broadcast signal into video data and audio data. The method according to claim 3, In step (d), a sequence parameter set (SPS) and a picture parameter set (PPS) are extracted from the digital broadcast signal, added to the front of the video region of the digital broadcast data, and audio decoder specification information is extracted from the digital broadcast signal. And generating the digital broadcast data by adding the digital broadcast data to the front of the audio region. The method according to claim 4, The step (d) includes compressing and generating the digital broadcast signal into digital broadcast data in RIFF format and storing the accumulated PTS value in a flag region of an index chunk according to RIFF format. Digital broadcast recording method characterized in that. The method according to claim 5, The step (d) includes storing information indicating whether the current frame is I frame using some bits of a length region of an index chunk included in the digital broadcast data of the RIFF format. Digital broadcast recording method characterized in that. The method according to any one of claims 2 to 6, (f) decoding and playing the digital broadcast data; And (g) When an FF / REW control signal is generated according to an external user control signal, a reproduction time point of each frame is calculated using the accumulated PTS value stored for each frame of the digital broadcast data, and the digital broadcast data is corresponding to the control signal. Moving the playing position of the; The digital broadcast recording method further comprises.

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