KR20080054034A - Broadcasting receiver and conditional access method - Google Patents

Abstract

A broadcast receiver and a reception limiting method are provided to provide various taste screen image services by simply changing a reception limitation setting to thus arouse user's interest to paid channels. A system decoder(102) separates a video bit stream from a transport stream and transmits it. A descrambler(103) receives the scrambled bit stream from the system decoder, and converts it into a bit stream that can be decoded by using a descramble key. A reception limitation controller limits a scratch of the descrambled video bit stream according to a set reception limitation mode. A picture scrambler scratches the bit stream by one of a picture or slide unit. A video decoder unit(105) performs decoding on the scratched bit stream.

Description

Broadcasting Receiver and Conditional Access Method

1 is a diagram illustrating a conventional general broadcast receiver.

2 is a diagram illustrating an example of a broadcast receiver with a reception restriction function according to the present invention;

3 is a block diagram illustrating an example of a control flowchart of a picture scrambler according to the present invention;

4 illustrates an example of a picture scratch according to the present invention.

Explanation of symbols for the main parts of the drawings

202: system decoder 203: descrambler

204: reception limit control unit 205: picture scrambler

206: VBV buffer 207: video decoder

The present invention relates to a method and an apparatus for restricting reception of an image.

Digital TV reduces transmission errors compared to analog TV to prevent noise and overlapping images to achieve high sound quality and high picture quality. In addition, by efficiently compressing and transmitting data such as voice, video, and text by using excellent digital compression technology, it is possible to transmit multiple channels to one channel of existing TV by reducing the amount of data required for one channel. Information can be provided.

While traditional TVs merely aim to transmit unilateral audio and video, digital TVs have the advantage of transmitting complex and diverse information relatively easily without error, recovering the original video and audio, and displaying them on the screen and speakers. .

Digital TV's video compression method uses the Moving Picture Expert Group (MPEG) standard. The basic framework of this compression method is to divide the continuous video frames constituting the video into blocks of a certain size and to provide spatial redundancy and time according to each block position. It is a technique to remove redundant redundancy. In other words, in order to remove spatial redundancy, the data in the pixel domain is converted into the frequency domain and quantized, thereby removing high frequency components that are not visually sensitive and reducing the amount of data to be transmitted. In addition, as a method of eliminating temporal redundancy, a portion having a pixel value similar to the current image frame is found from the reference image frame using motion estimation and compensation techniques, and then encoded into a motion vector, and the difference is frequency transformed. Encoding is performed.

The type of video frame of an MPEG video has I (Intra), P (Predictive), and B (Bi-predictive) according to the encoding method. The I frame is an image frame that can be restored on its own without requiring another reference frame. The P frame requires one reference frame decoded first in decoding order, and the B frame requires two reference frames decoded first in decoding order.

Since the I frame can be restored by itself without a reference frame, the video decoder is refreshed by eliminating error accumulation due to motion compensation. In addition, an I or P frame is used as a reference frame called an anchor frame, but a B frame is not used as a reference frame of a subsequent P or B frame. All macro blocks included in an I frame have only an intra macroblock type, and macro blocks included in a P frame have an intra or Motion Compensated (MC) macroblock type, and macro blocks included in a B frame are intra It has macro block type such as, Forward, Backward, Interpolated.

Recently, the reception restriction in digital TV is a necessary function in order to restrict viewing according to program grade, prevent unauthorized viewing of paid channels, and copyright protection.

As a general method for limiting the reception of a digital TV, an authentication device issued to a user authorized at the receiving end is scrambled by using a certain key for a transport stream where video and audio are multiplexed at the transmitting end. It is descrambled by the scramble key to restore the video and audio. The encryption method used for scrambling varies according to the digital TV transmission standard or the digital video storage medium standard.

1 shows a broadcast receiver equipped with a general transport stream descrambler according to the prior art.

The tuner 101 tunes a desired channel and outputs it to the system decoder 102 in the form of a transport stream (TS). The system decoder 102 selects one desired program when a plurality of programs are multiplexed on one channel. In this case, when the selected program is encrypted, the selected program is output to the descrambler 103, and the descrambler 103 receives the descrambler key to descramble the encrypted program and outputs the descrambled program to the system decoder 102.

The system decoder 102 separates the video bit stream and the audio bit stream from the descrambled TS, and then outputs the separated audio bit stream to the audio decoder 106. The separated video bit stream is also output to the video decoder 105 through the VBV buffer 104. The video signal decoded by the video decoder 105 is stored in the frame memory 107, and the video post processor 108 stores the frame memory.

The video signal stored at 107 is read and displayed by performing a process such as picture reordering or format conversion.

Therefore, according to the related art, a program corresponding to a paid channel scrambles the entire multiplexed transport stream using an encryptor, and thus access to the program itself is impossible in a receiver without an authentication key.

Frequently, paid channel service providers try to induce curiosity and viewing demands by providing viewers with some screen or voice of the program in order to attract and acquire more subscribers. According to the related art, a method of preventing a smooth viewing by controlling a decoder to prevent the reconstruction of some screens or voices on a frame-by-frame basis or by applying a scratch form to a fully restored screen or voice.

However, when providing a taste screen using the prior art, all the functions of the decoder required to restore the image have to be operated, so that the power consumption of the decoder increases. There is a problem that can not be limited.

Accordingly, an object of the present invention is to provide a broadcast receiver and a parental control method having an effective parental control system at a low cost by scrambling a video bit stream by a simple device by improving the inefficiency of scramble for a transport stream for reception restriction. Is in.

In order to achieve the above object, the broadcast receiver according to the present invention,

A system decoder for separating and transmitting the video bit stream from the transport stream; A descrambler that receives the scrambled bitstream from the system decoder and converts the scrambled bitstream into a decodable bitstream form using a descramble key; A reception limit control unit configured to limit scratches of the descrambled video bit stream according to a set reception limit mode; A picture scrambler applying a scratch to a bit stream in either a picture or a slice unit according to the control of the reception restriction control unit; And a video decoder to perform decoding on the scratched bit stream.

The reception restriction controller may set one or more of a mode for scratching only a corresponding picture or a mode for scratching a slice.

The picture scrambler may modify a parameter of a picture header when the entire picture of a corresponding coding type is scratched according to the reception restriction mode.

The picture scrambler may modify a bit stream corresponding to the first macroblock of each slice when the slice unit is scratched according to the reception restriction mode.

The reception restriction method according to the present invention includes the steps of: checking a reception restriction mode of a selected program; Scratching on a picture basis or on a slice basis according to the identified reception restriction mode; And decoding and outputting the scratched picture or slice.

The checking may include determining whether to block the entire picture or block each slice.

The scratching step may include: searching for a start of a picture to be scratched when the reception restriction mode blocks the entire picture for each picture coding type; And changing a header parameter value of the picture.

The scratch step may include: searching for the start of a slice to be scratched when the reception restriction mode blocks the slice; And changing the bit stream corresponding to the first macro block of the slice.

The changing may include changing a variable length code corresponding to the number and type of the macroblock.

The objects, features and advantages of the present invention will become apparent from the detailed description of the embodiments with reference to the accompanying drawings.

Hereinafter, with reference to the accompanying drawings, preferred embodiments of the present invention that can specifically realize the above object will be described. At this time, the configuration and operation of the present invention shown in the drawings and described by it will be described as at least one embodiment, by which the technical spirit of the present invention and its core configuration and operation is not limited.

Figure 2 is a detailed block diagram showing an embodiment of a broadcast receiver with a parental control function according to the present invention.

The tuner 201 tunes a desired channel and outputs it to the system decoder 202 in the form of a transport stream (TS). The system decoder 202 selects a desired program when a plurality of programs are multiplexed on one channel. In this case, when the selected program is scrambled, the system decoder 202 outputs the scrambled bitstream to the descrambler 203, and the descrambler 203 receives the descrambled key to decode the encrypted program. The data is converted into a form and output to the system decoder 202.

The picture scrambler 205, which is a device proposed by the present invention, performs a function of providing a part of a screen to a viewer by applying a scratch to a video bitstream according to a reception restriction mode of an unauthenticated receiver. The picture scrambler 205 of the receiver receives the video bit stream output from the system decoder 202 and scratches the video bit stream. At this time, the reception restriction control unit 204 sets the reception restriction mode at the input terminal to determine how much screen is temporarily displayed to the viewer.

The modes that determine the degree of screen viewing are classified as shown in Table 1.

In Table 1, the system decoder 202 is set to not descramble in a mode in which the entire video screen is blocked, and thus the video decoder 207 cannot be converted into a bitstream form decodable by the descrambler 203. A non-reproducible bitstream is input to the. In this case, the picture scrambler 205 may store the non-reproducible bitstream in the VBV buffer 206 without operating.

In a mode other than the entire blocking mode, the descrambler 203 converts the descrambler to a decodable bitstream using a temporary key and then applies the picture to the picture scrambler 205 through the system decoder 202. The picture scrambler 205 uses a picture scramble to be examined below to scratch the entire screen corresponding to the picture type, and uses an MB (macro block) scramble to be examined below to scratch a part of the screen, that is, a slice unit.

3 is a flowchart illustrating an embodiment of a picture scrambler that applies scratches to a screen according to picture scramble and MB scramble.

When the selected program is scrambled and blocks the entire video screen, the picture scrambler 205 does not operate as described above, and the picture scrambler does not operate even when the program is not blocked. In the other cases of the reception restriction mode, the picture scrambler operates (S301).

It is determined whether the selected program blocks the entire picture for each picture coding type or blocks each slice unit separately from the picture coding type. (S302) If the entire picture is blocked as a result of the determination, the picture searching step (S303). Finds the start of a valid picture by searching a value of 0x00000100, which is a value on the bit stream, which is a code indicating the start of a valid picture in the input bit stream.

The code indicating the start of the picture is composed of start_code_prefix and start_code_value. The start_code_prefix is 0x000001 and the Start code value is defined as shown in Table 2 below. At this time, since picture_start_code is 0x00, in the picture search step (S303), the start of a picture to be blocked must be found, so a value of 0x00000100 is searched.

As an example of a method of scratching a picture, when an entire picture is scratched by a picture scramble method, an important parameter of a picture header is transformed into a parameter having an invalid value to prevent proper picture decoding (S304). Examples of performing this include the following methods.

As shown in Table 3 below, the coding type of the picture is changed by adding 1 to the picture_coding_type value so that the decoding of the corresponding picture is not performed properly in the video decoder by changing the coding type of the picture. That is, picture type (picture_coding_type) = picture_coding_type + 1. For example, assuming that a picture type (picture_coding_type) value is 001 (that is, an intra picture), adding 1 to the picture_coding_type value converts an I picture into a P picture.

Alternatively, after finding the start code of 0x000001B58, the extension parameter of the picture is changed. The picture coding extension represents the unique features of the current picture and changes these values so that the video decoder does not decode the picture properly. This method is changed to f_code = 0, which represents a search region of a motion vector, that is, f_code represents a search region of a motion vector, and since a value of 0 is not used, decoding is not properly performed.

Alternatively, as shown in Table 4, a method of adding intra_dc_precision = intra_dc_precision + 1 by adding 1 to intra_dc_precision, which is a value indicating the number of bits (accuracy) of the DC coefficient of the intra-coded block, may be used.

 Alternatively, picture_structure, which is a value representing a picture structure, may have a value of zero. This is changed to the reserved code so that the decoder does not decode properly.

Alternatively, although not mentioned in the present invention, a picture scratch may be performed by a designer by changing a picture code value other than the above-mentioned code.

In the picture scratch step (S304), the parameter value corresponding to the picture header information is changed to another value or a meaningless value so that the decoder cannot decode the picture properly so that an image that is difficult to recognize is displayed on the screen. .

If there are no pictures to be scratched, the picture scrambler ends, and if there are remaining pictures to be scratched, the picture scrambler goes to a picture searching step (S303).

If it is determined in step S302 that the picture is not in the entire block mode, that is, in the case of scratches in a slice unit, the slice search step S306 searches for the start code of the slice to be scrambled. In Table 2, slice start codes are distributed from 0x00000101 to 0x000001AF, and slice numbers having a value of 01 to AF generally indicate vertical positions in units of MB (macro block).

In the first MB scratch step (S307), the bitstream corresponding to the first macroblock of each slice is modified to prevent proper decoding. In an embodiment of scratching a slice, the slice number may be set to scratch the slice. In this case, an example of setting a slice to be scratched may include setting an odd or even row or setting a scratch every N slices.

As the encoding method of the slice stage of the bitstream, fixed length encoding and variable length encoding are used together. However, the encoding scheme in macroblock units generally uses variable length encoding. Therefore, if the first macroblock is scratched, the subsequent variable length code is not properly restored, and thus the scratch effect is generated until the next valid start code appears. This makes it possible to scratch the entire slice.

Macro block scratches are performed in the following manner. In the slice or macro block, the existing value is maintained until another quantization scale code value exists. The quantiser_scale_code, which means the quantization scale value, is set to 0 to prevent proper decoding in the video decoder.

Alternatively, the macroblock_address_increment, expressed as a variable length code that is the difference between the current macroblock address macroblock_address and the previous macroblock address previous_macroblock_address, is inverted for 32 bits from the starting position, that is, '0' to '1' and '1' to ' 0 'prevents proper decoding.

Or a variable length coded variable for the type of the macroblock, with a macroblock_type of 16 bits at its starting position, depending on whether there is a picture format and scalability, and if so, what scalability is applied. Invert to prevent proper decoding.

If you invert bits as above, the subsequent variable length code is decoded to a value different from the original code, and the screen is not restored properly. The number of bits to be inverted is larger than the maximum length of the corresponding code. The bit is reversed.

Alternatively, although not mentioned in the present invention, a slice scratch may be performed by changing a macroblock code value other than the above-mentioned code by a designer.

If there are no slices to scratch, the picture scrambler ends, and if there are remaining slices to scratch, the picture scrambler goes to a slice search (S306) step (S308).

4A, 4B, and 4C show an example of a screen scratched by the picture scrambler. Figure 4a shows the original I picture before scratching. If one slice of this I picture consists of one macroblock row, Figure 4b shows the result of scratching every odd slice. If you apply slice to I picture like this, in the following picture, scratch applied to the previous reference picture is spread as the picture is crushed, and the screen is crushed and the proper picture is not shown.

If you apply such a scratch, you can see the outline of the screen except the scratched slice on the screen where the I picture starts from the whole picture, but after that, the picture will be crushed and you may be curious about the progress of the picture. Can be. To increase the degree of scratch on the screen depending on the content of the image, you can increase the slice to be scratched further.

On the other hand, the terms used in the present invention are defined terms in consideration of functions in the present invention may vary according to the intention or customs of those skilled in the art, the definition should be changed based on the overall contents of the present invention. something to do.

In addition, the present invention is not limited to the above-described embodiments, and can be modified by those skilled in the art as can be seen from the appended claims, and such modifications are within the scope of the present invention.

According to the above-described apparatus and method for restricting viewing of a video of a broadcast receiver according to the present invention, by performing scrambling according to each picture or slice to restrict viewing, it is possible to reconstruct the image using only a part of a video decoder during decoding. It has the effect of reducing power consumption.

In addition, the present invention has the effect of causing the viewer's curiosity and desire to watch for a paid channel by simply changing the reception restriction setting to provide a variety of taste screen service.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the spirit of the present invention.

Therefore, the technical scope of the present invention should not be limited to the contents described in the embodiments, but should be defined by the claims.

Claims (9)

A system decoder for separating and transmitting the video bit stream from the transport stream; A descrambler that receives the scrambled bitstream from the system decoder and converts the scrambled bitstream into a decodable bitstream form using a descramble key; A reception limit control unit configured to limit scratches of the descrambled video bit stream according to a set reception limit mode; A picture scrambler applying a scratch to a bit stream in either a picture or a slice unit according to the control of the reception limiting control unit; And And a video decoder for decoding the scratched bit stream. The method of claim 1, wherein the reception restriction control unit And at least one of a mode for scratching only a corresponding picture or a mode for scratching a slice. The method of claim 1, wherein the picture scrambler And a parameter of a picture header is modified when an entire picture of a corresponding coding type is scratched according to the reception restriction mode. The method of claim 1, wherein the picture scrambler And a bit stream corresponding to the first macro block of each slice is modified when the slice unit is scratched according to the reception restriction mode.  Confirming a reception restriction mode of the selected program; Scratching on a picture basis or on a slice basis according to the identified reception restriction mode; And Decoding and outputting the scratched picture or slice. The method of claim 5, wherein the checking step And determining whether to block the entire picture or block each slice. The method of claim 5, wherein the scratch step Searching for the start of a picture to be scratched when the reception restriction mode blocks the entire picture for each picture coding type; And changing a header parameter value of the picture. The method of claim 5, wherein the scratch step Searching for the beginning of a slice to scratch if the reception restriction mode blocks a slice; And changing the bit stream corresponding to the first macro block of the slice.  9. The method of claim 8, wherein said changing And a variable length code corresponding to the number and type of the macroblock.

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