KR100370059B1 - Video codec and method for transmitting/receiving video data using the same - Google Patents

Abstract

The present invention relates to a video codec and a video data transmission / reception method using the same, which is suitable for stably transmitting video data in a wireless environment. The image data transmission and reception method according to the present invention includes the steps of inputting an image frame, compressing the input image frame by discrete cosine transform, encoding the compressed image frame, and encoding the encoded image frame. Detecting a picture start code at step S, and detecting state information of an encoded channel buffer according to a comparison result of the detected picture start code and a pre-stored picture start code, and detecting the state information of the detected coded channel buffer by using the encoded image. Inserting a frame into a frame, receiving the image frame, detecting a picture start code from the received image frame, comparing the picture start code with a pre-stored picture start code, and transmitting the image frame according to the comparison result Detecting status information of a transmission-side encoded channel buffer; Adjusting the operating speed of the variable length decoding according to the state information submitted and,By adjusting the state of the decoding channel buffer according to the adjusted operation speed Decoding the received video frame has an effect of optimizing the channel buffer state of the decoder to provide a video service of a certain quality.

Description

Video codec and method for transmitting / receiving video data using the same}

The present invention relates to a video codec, and more particularly, to a video codec and a video data transmission / reception method using the same, which is suitable for transmitting image data stably in a wireless environment.

The next generation mobile communication (IMT-2000), which is currently undergoing technical standardization, will provide a video service using a video terminal. This is possible because next generation mobile communication uses wideband frequency unlike conventional mobile communication. At this time, the video terminal under development for the next generation mobile communication is essentially equipped with a video codec composed of an encoder and a decoder so as to code and decode video data. The technical standard for the video codec is H of ITU-T. Defined in .263 (see ITU-T Recommendation H.263, DRAFT H.263 27 January, 1998).

The following describes the operation of the video codec defined in H.263 of the ITU-T.

1 is a block diagram illustrating an encoder according to the prior art.

Referring to FIG. 1, a conventional encoder may further include a core part 100 compressing an image by performing motion compensation, discrete cosine transform, and quantization on an input image frame, and a compressed image frame. A variable length encoder (VLC) 110 for encoding a small bit amount and an encoding channel buffer 120 for transmitting a final coded video frame at a fixed data rate. The core part 100 may include a DCT unit 101 for discrete cosine transforming an image frame, a quantization unit 103 for quantizing the image frame, and an inverse quantization unit 104 for inverse quantization of the quantized image frame. ), An IDCT unit 105 for inverse discrete cosine transform, a frame memory 106 for storing an inverse quantized image frame, and a motion compensation unit for estimating and compensating for a motion difference between the quantized image frame and the initial image frame. 107 and the motion estimation unit 108.

The operation of the encoder configured as described above is as follows.

First, the DCT unit 101 of the core unit 100 receives an image frame and compresses it by performing discrete cosine transform, and the quantization unit 103 performs quantization to discard high frequency terms of the compressed image data. Next, the variable length encoder (VLC) 110 finally encodes the quantized image data into bit strings having various bit lengths. In this case, the encoded final bit string is temporarily stored in the encoding channel buffer 120 and then transmitted to the receiving side decoder through a communication channel.

2 is a block diagram illustrating a decoder according to the prior art.

Referring to FIG. 2, the conventional decoder includes a decoding channel buffer 200 for receiving an image frame, a variable length decoder (VLD) 210 for decoding an image frame input to the decoding channel buffer 200, and a variable length. It is composed of a core part (220) for restoring image compression by inverse quantization and inverse discrete cosine transform the image frame output from the decoder (210). The core unit 220 includes an inverse quantization unit 221, an IDCT unit 222, a frame memory 224, and a motion compensation unit 223.

The operation of the decoder configured as described above is as follows.

First, the decoding channel buffer 200 receives and stores an image frame transmitted through a wireless channel. The variable length decoder (VLD) 210 and the core unit 220 inversely quantize and inverse discrete cosine transform (IDCT) the stored image frame when the image frame is input and stored at a predetermined level in the decoding channel buffer 200. Restore the original image.

In the conventional encoder described above, the encoding channel buffer 120 is a buffer that exists to transmit the variable bit rate image data generated by the variable length encoder 110 at a fixed bit rate through a communication channel. Therefore, the encoding channel buffer 120 overflows, which is a phenomenon in which data in the buffer overflows when the image data of the average length is output from the variable length encoder 110 at a moment, and the image below the average size from the variable length encoder 110. It has a sufficient size so that underflow, a phenomenon in which data in a buffer is depleted when data is output, does not occur.

However, since the encoder performs control according to the output change of the image data using the rate controller 100 even if the size of the encoding channel buffer 20 is not large, overflow and underflow do not occur in the encoding channel buffer 120. .

On the other hand, the decoder does not have a rate controller. Therefore, the decoder controls the state of the decoding channel buffer 200 by synchronizing the state of the encoding channel buffer 120 with the state of its decoding channel buffer 200 before the decoding operation.

In more detail, the encoder and the decoder start to operate when the image data is half-filled in the channel buffer. Therefore, the encoder starts to transmit the image data through the communication channel when the image data is half-filled in the encoding channel buffer 120. Similarly, the decoder also decodes the image data when the image data is half-filled in the decoding channel buffer 200. To start.

Therefore, in the conventional video codec, when the encoder adjusts the state of an encoding channel buffer using a rate controller, the decoder also adjusts the state of the decoding channel buffer.

3A to 3C are diagrams illustrating operation states of a conventional encoding channel buffer and a decoding channel buffer.

Referring to FIG. 3A, as described above, the channel buffers of the encoder and the decoder operate in synchronization with each other. At this time, the operation starts when the same amount, that is, intermediate image data is filled.

Referring to FIG. 3B, when a large amount of image data is generated at an instant in an encoder after an initial state, an encoding channel buffer is filled with a medium or more. The decoder then relatively decodes the image data at a rate above average, thus freeing the decoding channel buffer below halfway.

Referring to FIG. 3C, unlike FIG. 3B, when a small amount of image data is generated at an instant in an encoder, the encoding channel buffer is emptied to the middle or less. The decoder then relatively decodes the image data at a sub-average rate so that the decoding channel buffer is filled with more than halfway. In this operation, if the encoder buffer is controlled to prevent overflow or underflow, the decoder channel buffer also operates stably because the decoder moves according to the state of the encoder.

However, since the operation of the conventional encoder and decoder does not consider the characteristics of the communication channel, the following problems occur.

Since the communication channel has a high channel error rate (BER), video data transmitted through the communication channel is likely to be broken due to an error.

When such a situation occurs, the conventional encoder stops the operation without transmitting the image data for a predetermined time, and accordingly, an underflow of the image buffer becomes empty in the channel buffer of the decoder.

Underflow like this If a conventional video codec is applied to a video terminal as it causes malfunction of the decoder, it cannot provide a video service of a certain quality.

Accordingly, an object of the present invention is to provide a video codec and a video data transmission / reception method using the same, which are devised in view of the above-mentioned problems of the related art, which stabilizes the operation of a channel buffer to optimize the operation of a video codec. .

According to an aspect of the present invention for achieving the above object, the video codec is a core unit for discrete cosine transform the input image frame and compresses, the compressed image frame is encoded, the image output from the core unit A variable length encoder for adding a dummy code region to a frame, an encoding channel buffer for storing the encoded image frame, an image frame from the encoding channel buffer, and receiving a picture start code from the received image frame And a buffer state inserter for detecting the state of the encoded channel buffer by detecting and comparing the stored picture start code with a pre-stored picture start code, and inserting the detected state of the encoded channel buffer into a dummy code region of the image frame. An encoder and a picture in an image frame transmitted from the encoder A buffer status detector that detects a tart code and compares it with a pre-stored picture start code, and detects state information of a transmission-side encoded channel buffer that has transmitted the video frame according to the comparison result, and according to the detected state information. A decoding channel buffer operating in synchronization with the state of the encoding channel buffer, and a variable length decoder for adjusting a decoding speed of the decoding channel buffer in synchronization with the state of the encoding channel buffer according to the detected state information. And a core unit configured to restore the image frame output from the variable length decoder by motion compensation and inverse discrete cosine transform.

According to another aspect of the present invention for achieving the above object, the image data transmission and reception method comprises the steps of inputting an image frame, compressing the input image frame by discrete cosine transform, and the compressed image frame Detecting a picture start code in the encoded image frame, detecting state information of an encoding channel buffer according to a comparison result of the detected picture start code and a pre-stored picture start code, and detecting the picture start code. Inserting state information of an encoding channel buffer into the encoded image frame and transmitting the state information; Receiving the video frame, detecting a picture start code in the received picture frame, comparing the picture start code with a pre-stored picture start code, and comparing the state information of the transmission-side encoded channel buffer that transmitted the picture frame according to the comparison result. Detecting, and adjusting an operation speed of the variable length decoder according to the detected state information.,By adjusting the state of the decoding channel buffer according to the adjusted operation speed And decoding the received video frame.

1 is a block diagram showing an encoder according to the prior art.

2 is a block diagram illustrating a decoder according to the prior art.

3A to 3C are diagrams illustrating operation states of a conventional encoding channel buffer and a decoding channel buffer.

4A is a block diagram illustrating an encoder according to a first embodiment of the present invention.

4B is a block diagram illustrating a decoder in accordance with a first embodiment of the present invention.

5A is a block diagram illustrating an encoder according to a second embodiment of the present invention.

5B is a block diagram illustrating a decoder in accordance with a second embodiment of the present invention.

FIG. 6 is a detailed circuit diagram of the buffer state inserter shown in FIG. 5A. FIG.

7A illustrates the structure of a conventional video frame.

7b is a diagram showing the structure of an image frame according to the present invention;

* Description of the symbols for the main parts of the drawings *

400, 405: core part 401: variable length encoder (VLC)

402: encoding channel buffer 403: decoding channel buffer

404 variable length decoder (VLD)

Hereinafter, a configuration and an operation according to an exemplary embodiment of the present invention will be described with reference to the accompanying drawings.

The present invention proposes a video codec and a method for transmitting and receiving video data using the same, which provides a video service having a certain quality by stabilizing a channel buffer of an encoder and a decoder.

To this end, the present invention provides a channel buffer state of the encoder to the decoder so that the decoder can perform optimized decoding by stabilizing the channel buffer regardless of whether an error occurs in an image frame transmitted through a wireless channel.

In order to inform the decoder of the channel buffer status of the encoder as described above, the encoder according to the present invention additionally inserts buffer status information (hereinafter, abbreviated as CBS) into the video frame and encodes the video frame to the decoder, and sends the same to the decoder. The decoder detects the channel buffer state of the encoder by detecting the CBS from the transmitted image frame, and operates the channel buffer state of the encoder according to the channel buffer state of the encoder.

Herein, in the present invention, the insertion of the CBS can be implemented in two ways, which will be described in detail in the first and second embodiments.

First embodiment

In the first embodiment, a video codec and an image data transmission method for inserting and transmitting a CBS in an image frame by an encoder by itself without adding additional hardware to the video codec and detecting the inserted CBS from the image frame transmitted by the decoder. Suggest.

4A is a block diagram illustrating an encoder according to a first embodiment of the present invention.

Referring to FIG. 4A, the encoder according to the first embodiment compresses an image by performing motion compensation, discrete cosine transform, and quantization on an input image frame, and an encoding channel buffer 402. It consists of a variable length encoder 401 for inserting a CBS into an image frame, and an encoding channel buffer 402 for informing its state to the variable length encoder 401.

In this case, the core unit 400 performs the same function as in the related art, and the variable length encoder 401 applies a CBS indicating the state of the encoding channel buffer 402 to an image frame according to the state information provided by the encoding channel buffer 402. Insert additionally. At this time, the variable length encoder 401 periodically inserts the CBS into the image frame. Preferably, the variable length encoder 401 inserts a CBS for each image frame.

As described above, the encoder proposed in the first embodiment provides its state information to the variable length encoder 401 in the encoding channel buffer 402, and the variable length encoder 401 inserts the CBS into the image frame.

4B is a block diagram illustrating a decoder in accordance with a first embodiment of the present invention.

Referring to FIG. 4B, the decoder according to the first embodiment includes a decoding channel buffer 403 for receiving an encoded image frame, a variable length decoder 404 for decoding the encoded image frame, and a variable length decoder ( And a core unit 405 for restoring by inverse discrete cosine transforming and inverse quantization of the image frame output from the 404.

Here, the variable length decoder 404 detects the CBS from the received image frame and detects the state of the encoding channel buffer 402. The decoding channel buffer 403 operates in synchronization with the state of the encoding channel buffer 402 by providing the detected state information of the encoding channel buffer 402 to the decoding channel buffer 403.

That is, the decoder suspends the decoding operation on the decoding channel buffer 403 when the decoding channel buffer 403 is in an underflow state when compared with the status of the encoding channel buffer 402 detected from the image frame. On the other hand, in an overflow state, the decoding speed of the decoding channel buffer 403 is increased so that the decoding channel buffer 403 is synchronized with the encoding channel buffer 402.

This operation is possible because the state of the encoding channel buffer 402 can be detected when encoding the image frame from the CBS inserted in the image frame.

As described above, the decoder proposed in the first embodiment detects the state of the encoding channel buffer 402 from the image frame received by the variable length decoder 404 and adapts the operation of the decoding channel buffer 403 accordingly.

The encoding channel buffer 402 provides its state information to the variable length encoder 401, and the variable length encoder 401 inserts the CBS into the image frame.

Second embodiment

The second embodiment proposes a video codec and a video data transmission method in which additional hardware is added to a video codec to inform a decoder of a state of an encoding channel buffer.

5A is a block diagram illustrating an encoder according to a second embodiment of the present invention.

Referring to FIG. 5A, the encoder according to the second embodiment compresses an image by performing motion compensation, discrete cosine transform, and quantization on an image frame, and compresses the compressed image frame with a smaller data amount. A variable length encoder 501 for encoding, an encoding channel buffer 502 for transmitting the last encoded image frame at a fixed data rate, and a buffer state for inserting CBS into the image frame according to the states of the encoding channel buffer 502. It is composed of an inserter 503.

Referring to the operation of the encoder configured as described above, the variable length encoder 501 first adds a dummy code having a predetermined area after the PSC code of the image frame compressed and output from the core unit 500.

The buffer state inserter 503 then detects the PSC code of each image frame, and inserts the CBS code into the dummy code area already added after the detected PSC code. In this case, the buffer state inserter 503 detects the state of the encoding channel buffer 502 according to the buffer state information provided from the encoding channel buffer 502.

As described above, the encoder proposed in the second embodiment provides its state information to the buffer state inserter 503 in the encoding channel buffer 502, and the buffer state inserter 503 inserts the CBS into the image frame. .

5B is a block diagram illustrating a decoder in accordance with a second embodiment of the present invention.

Referring to FIG. 5B, the decoder according to the second embodiment detects a CBS from an image frame and provides a buffer state detector 504 for providing the state information of the encoding channel buffer 502 to the decoding channel buffer 505. The decoding channel buffer 505 operating in synchronization with the encoding channel buffer 502 according to the state information of the encoding channel buffer 502 provided by the buffer state detector 504, and the encoding provided by the buffer state detector 504. The variable length decoder 506 adjusts the decoding speed of the image frame input to the decoding channel buffer 505 according to the state information of the channel buffer 502, and the image frame output from the variable length decoder 506 is reversed. It consists of a core portion 507 for quantization and inverse discrete cosine transform.

The operation of the decoder configured as described above is as follows.

First, the buffer state detector 504 receives an image frame transmitted from the encoder, and then detects a CBS indicating the state of the encoding channel buffer 502 from the received image frame.

In this case, since the CBS is positioned after the PSC code of the image frame, the buffer status detector 504 detects the CBS by finding the PSC code of each image frame.

The buffer state detector 504 reads the detected CBS and then provides the state information of the encoding channel buffer 502 to the decoding channel buffer 505 accordingly.

The decoding channel buffer 505 then operates in synchronization with the encoding channel buffer 502 according to the state information of the encoding channel buffer 502 provided from the buffer state detector 504.

In this case, the variable length decoder 506 adjusts the decoding speed of the decoding channel buffer 502 according to the detected state information of the encoding channel buffer 502.

As described above, the decoder proposed in the second embodiment detects the state of the encoding channel buffer 502 from the image frame received by the buffer state detector 504 and adapts the operation of the decoding channel buffer 505 accordingly.

FIG. 6 is a detailed circuit diagram of the buffer state inserter shown in FIG. 5A.

Referring to FIG. 6, the buffer state inserter inserts a PSC code register (Picture Start Code Register) 600 storing a PSC code, a comparator 601 for detecting a PSC code of image data, and inserts a CBS into an image frame. Consisting of a CBS inserter 602.

The operation of the buffer state inserter configured as described above is as follows.

First, the PSC code register 600 stores a PSC code. When the image frame is input, the comparator 601 detects the PSC code of the image frame by comparing the input image frame with the PSC code provided from the PSC code register 600.

When the PSC code of the video frame is detected, the CBS inserter 602 inserts a CBS indicating the state of the encoding channel buffer 502 into the video frame at the time of detecting the PSC code. At this time, the CBS is inserted into a region where the dummy code is transmitted by the variable length encoder 501. In the present invention, the CBS is inserted after the PSC code.

Meanwhile, the buffer state detector 504 of the decoder has the same configuration as the buffer state inserter 503.

That is, a PSC code register (not shown) that stores a PSC code, a comparator (not shown), and a CBS detector (not shown) are configured to find the PSC code from the transmitted image frame, and then detect the corresponding CBS code.

7A is a diagram illustrating the structure of a conventional image frame, and FIG. 7B is a diagram illustrating the structure of an image frame according to the present invention.

7A to 7B, header information of a conventional video frame has a configuration as shown in FIG. 7A as defined in H.263. In the present invention, since the CBS code indicating the state of the encoding channel buffer is inserted after the PSC code, the structure of an image frame according to the present invention is shown in FIG. 7B.

Meanwhile, in the first embodiment, a predetermined difference may occur between the CBS insertion time in the encoder and the CBS detection time in the decoder.

That is, in the first embodiment, since the CBS is directly inserted into the image frame and the CBS is directly detected by the variable length decoder, the insertion time and the detection time of the CBS are determined by the pass time of the encoding channel buffer, the radio channel pass time, It exists as long as the pass time of the decoding channel buffer.

Accordingly, there is a disadvantage in that the actual encoding channel buffer state and the detected encoding channel buffer state may be different at the time when the decoder detects the CBS.

On the other hand, in the second embodiment, since the insertion and detection of the CBS is processed using separate hardware, the insertion time and the detection time of the CBS are reduced to the passage time of the radio channel. This means that the insertion time and the detection time of the CBS have a minimum difference. Therefore, the actual coding channel buffer state and the detected coding channel buffer state are mutually different. Similar.

As described above, according to the video codec and the image data transmitting / receiving method using the same according to the present invention, the decoder periodically informs the channel buffer state of the encoder, thereby optimizing the channel buffer state of the decoder to provide a video service of a certain quality. There is.

In particular, when the video codec according to the present invention is applied to a video terminal transmitting video data through a wireless channel, an excellent effect of preventing the decoder from malfunctioning by optimizing the channel buffer state of the decoder regardless of whether there is an error in the video frame is obtained. have.

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 examples, but should be defined by the claims.

Claims (7)

A core unit for discrete-cosine transforming and compressing an input image frame, a variable length encoder for encoding the compressed image frame, and adding a dummy code region to the image frame output from the core unit, and Receives an encoded channel buffer storing an image frame and an image frame from the encoded channel buffer, detects a picture start code from the received image frame, and compares the state of the encoded channel buffer with a prestored picture start code. An encoder including a buffer state inserter for sensing and inserting state information of the detected encoded channel buffer into a dummy code region of the image frame; A buffer state detector which detects a picture start code from an image frame transmitted from the encoder and compares the picture start code with a prestored picture start code, and detects state information of a transmission-side encoded channel buffer that transmitted the image frame according to the comparison result. And a decoding channel buffer operating in synchronization with a state of the encoding channel buffer according to the detected state information, and a decoding rate for the decoding channel buffer according to the detected state information is synchronized with a state of the encoding channel buffer. And a decoder including a core for reconstructing and reconstructing a video frame output from the variable length decoder by motion compensation and inverse discrete cosine transform. delete Inputting an image frame; Compressing the input image frame by discrete cosine transform; Encoding the compressed video frame; Detecting a picture start code from the encoded image frame and detecting state information of an encoding channel buffer according to a result of comparing the detected picture start code with a pre-stored picture start code; Inserting and transmitting state information of the detected encoded channel buffer into the encoded image frame; Receiving the image frame; Detecting a picture start code from the received picture frame, comparing the picture start code with a pre-stored picture start code, and detecting state information of a transmission-side encoded channel buffer transmitting the picture frame according to the comparison result; Adjusting an operation speed of a variable length decoder according to the detected state information ; By adjusting the state of the decoding channel buffer according to the adjusted operation speed And decoding the received video frame. The method of claim 3, further comprising: generating and adding a dummy code region to the compressed image frame; And inserting and transmitting state information about the encoded channel buffer in the added dummy code region. delete A core unit for compressing the input image frame by discrete cosine transform; An encoding channel buffer configured to output state information according to the amount of input data; An encoder including a variable length encoder encoding the image frame output from the core unit and inserting buffer state information into the encoded data according to the state information output from the encoding channel buffer; A decoded channel buffer for storing the image frame input from the encoder; A variable length decoder configured to receive an image frame in which buffer state information of the encoder is stored from the decoded channel buffer and to compare a state of the decoded channel buffer to control a decoding operation; And a decoder comprising a core unit for reconstructing and inversely quantizing inverse discrete cosine the image frame inputted from the variable length decoder. Compressing the input image frame by discrete cosine transform; Outputting state information according to the amount of data input to the encoded channel buffer; Encoding the compressed image frame and inserting buffer state information of an encoded channel buffer into the encoded data and transmitting the encoded image frame; Receiving the encoded image frame and controlling a decoding operation by using the buffer state information; And reconstructing the decoded data by inverse discrete cosine change and inverse quantization.