JP2002171530A - Re-encoder provided with superimpose function and its method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a re-encoder that applies superimpose processing to MPEG 2 video data by using a frame frequency different from that of an MPEG 2 stream so as to suppress image quality deterioration between decoding and encoding in the case of applying re-encoding to the MPEG 2 video data. SOLUTION: A video decoder 4 is provided with a function of outputting repeat field information 108 to a superimpose 5 and of outputting an MPEG 2 encoding parameter 105 to a video encoder 6. The superimpose 5 applies superimpose processing to video data 106 decoded in matching with a characteristic of an image to be superimposed and outputs superimpose field information 110 and superimpose area information 111 to the video encoder 6. The video encoder 6 re-encodes an output of the superimpose 5 while adaptively utilizing the MPEG 2 encoding parameter 105, the superimpose field information 110 and the superimpose area information 111.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to MPEG2 ("Gene
ric coding of Moving Pictures and associatedaudio
information ", ISO / IEC 13818) A superimpose function that superimposes text and image data on a stream generated by an image encoding device equipped with motion compensation The present invention relates to a re-encoding device and method provided.

[0002]

2. Description of the Related Art At present, analog broadcasting in Japan is 29.97.
A frame frequency of 2 Hz is used, and an analog VTR, a TV receiver, and the like generally used at home are 29.9.
It corresponds to a frame frequency of only 7 Hz. For this reason, when broadcasting a material such as a movie created at a frame frequency of 24 Hz, the frequency is reduced from 24 Hz, which is called a cine-tele conversion, to 29.29.
To perform conversion to 97 Hz, the same field image is repeated at regular intervals.

On the other hand, in digital broadcasting, image encoding using an image compression technique called the MPEG2 standard is performed in order to use a transmission band efficiently. ST at home
M using a digital receiver called B (Set Top Box)
Decodes PEG2 data and converts analog video signals to TV
Output to the receiver.

According to the MPEG2 standard, when the frame frequency or frame structure of a coded stream is different from the frame frequency or frame structure of the TV receiver, the STB performs frequency conversion and performs coding conversion so that the TV receiver can reproduce the frame. , Frame_rate_code, position information of a start field called top_field_first, repeat information of a next field called repeat_field_first, and the like.

[0005] Therefore, unlike the conventional analog broadcasting, digital broadcasting using the MPEG2 standard does not require cine-tele conversion at the time of encoding.

[0006] Also, as for broadcasting equipment used in a broadcasting station, a model using MPEG2 has been developed. The connection interface between such devices is a serial digital interface (SDI) used in conventional uncompressed digital devices.
ace) (SMPTE-259M standard) / HD-SDI (S
In the MPTE-292M standard), decoding (expansion) and encoding (compression) are repeated between interfaces, so that image quality deteriorates according to the number of transmissions.
SMPTE-31 as a method of directly transmitting a stream
OM standard: "Synchronous Serial Interface for MPEG-2
Digital Transport Streams "has been standardized.

[0007]

However, the above M
Adds various video effects and superimpose processing to PEG2 stream, 4: 2: 2/4: 2: 0 chroma format conversion, and transcoder (re-encoding device) to convert encoding rate Becomes

As described above, even in a broadcasting station, an MPEG2 stream is being used instead of an uncompressed digital interface as a transmission interface between devices. There is the following problem if it is different from the frame structure.

[0009] Hereinafter, a movie material of 24 Hz is converted to 29.97.
A description will be given of an example of conversion to a 480i / 60 Hz system, that is, a system in which 480 lines are scanned in 60 fields by interlace.

When performing a superimpose process or the like, M
When the PEG2 stream is decoded into a video signal, the superimposing process is performed, and the re-encoding process is performed, the image quality largely deteriorates. This was originally 2
When the data coded at 4 Hz is converted back to a video signal, it becomes 29.97 Hz. Since the signal of 29.97 Hz is subjected to the superimposing process, it must be coded at 29.97 Hz even at the time of re-encoding. This means that the coding efficiency is lowered and the image quality deterioration is easily perceived.

For example, assuming that a 24 Hz movie material in which one screen is composed of 720 pixels × 480 lines is encoded at a 6 Mbps encoding rate, the assigned code amount per pixel is 6,000,000 bps / ( 720
(Pixels × 480 lines × 24 Hz) = 0.72 bits, whereas when a repeat field is performed at an appropriate time and encoded at a frame frequency of 29.97 Hz, 6,000,00
00 bps / (720 pixels x 480 lines x 29.97
Hz) = 0.58 bits, and the code amount assigned per pixel is reduced to about 80%.

Accordingly, an object of the present invention is to generate an MPEG2 stream again while minimizing image quality degradation when performing superimpose processing on an MPEG2 stream having a frame frequency and a frame structure different from the broadcasting system. .

[0013]

In order to solve the above-mentioned problems, the present invention provides a re-encoding apparatus and method according to the first and fifth aspects of the present invention, in which a next field in a picture header which is an MPEG2 encoding parameter is repeated. With reference to the information, in synchronization with the decoded reproduced video signal, a function of outputting an identification signal indicating a picture start position and a repeat field position of an MPEG2 stream to a superimpose circuit, and detecting a superimposed area. And a function of outputting superimposed area information to a video encoder in synchronization with a video signal.

The re-encoding device and method according to the second and seventh aspects have a function of determining whether the image data to be superimposed is a still image or a moving image, and outputting it to a video encoder.

According to a third aspect of the present invention, there is provided a re-encoding apparatus and method wherein a superimposed image is a still image even when the frame frequency or frame structure of an MPEG2 stream is different from that of a broadcast system. A superimpose function that superimposes a superimposed image only on the field obtained by decoding the original MPEG2 stream, excluding the repeat field portion, and adaptively performs the same processing as normal superimposition processing when the moving image is a moving image. Prepare.

In the re-encoding apparatus and method according to the fourth and ninth aspects, when the superimposition area information does not exist, the encoding parameters obtained by the video decoder are reused to perform MPEG2 encoding, and the superimposition is performed. When the area information exists and the frame frequency information obtained from the MPEG2 stream is different from the frame frequency of the broadcasting method, the encoding parameters are not reused and the MPEG2 encoding is performed at the set frame frequency.

In the re-encoding apparatus and method according to the fifth and tenth aspects, when the superimposition area information does not exist, the encoding parameters obtained by the video decoder are reused to perform MPEG2 encoding, and the superimposition is performed. If the region information is present and the superimposed image is a still image, MPEG2 encoding is performed by reusing the encoding parameters obtained by the video decoder, and the superimposed image exists and the superimposed image is present. If is a moving image, the MPEG obtained from the video decoder
It is characterized in that MPEG2 encoding is performed without reusing two parameters.

[0018]

Next, embodiments of the present invention will be described with reference to the drawings. In the drawings, circuits having the same function are denoted by the same reference numerals.

FIG. 1 is a block diagram showing a system outline of a re-encoding device having a superimpose function according to the present invention. The TS decoder 1, the audio delay memory 2, the TS encoder 3, the video decoder 4, the superimpose. It comprises a circuit 5 and a video encoder 6.

The TS decoder 1 transmits the MPEG2
A video signal and an audio signal are separated from a TS (transport stream) 100, and the video signal is output to the video decoder 4 as an MPEG2 video stream 103, and the audio signal is output to the audio delay memory 2 as an audio stream 101.

The audio delay memory 2 is a delay memory for synchronizing the video signal and the audio signal. The audio delay memory 2 delays the audio stream 101 by the time when the video signal is delayed by the video encoder 4, the superimposing circuit 5, and the video encoder 6. , And outputs the delayed audio stream 102 to the TS encoder 3. Here, the audio stream is MPEG2
It is composed of data compressed by an encoding method, uncompressed PCM data, and the like. In the present embodiment, the delay memory for synchronizing with the video signal is used because the bit rate conversion and the post-recording processing (replacement) of the audio data are not assumed, but when the audio signal needs to be reprocessed, In addition to the delay memory 2, an audio encoder for reprocessing is required. Further, when data other than video and audio is included in the TS stream, it is necessary to use an external memory to delay and regenerate data. However, this embodiment is omitted because the main purpose is to process video signals. ing.

FIG. 2 shows a detailed circuit configuration example of the video decoder 4. The VLD (variable length code decoder) circuit 40, the inverse quantization circuit 41, the inverse DCT circuit 42, the motion compensation circuit 43, the parameter It comprises a memory 44 and a synchronization generation circuit 45.

The difference from the video decoder using the prior art is that the synchronization generation circuit 45 is used to synchronize the picture start information 107 and the repeat field position information 108 on the MPEG2 stream with the decoded video data 106 in super-in. Output to the pause circuit 5.

The VLD circuit 40 performs variable length decoding from the MPEG2 video stream 103,
05 to the parameter memory 44, and the quantized coefficient value data 123 as video data to the inverse quantization circuit 41.
Here, the coding parameter 105 includes the number of coding bits 126 for each macroblock, parameters below the sequence layer of the MPEG2 standard, frame frequency information, top field information, repeat field information, picture type, and number of coding bits for each frame 127. , VBV delay value, quantization matrix, macroblock type, motion vector data 122, quantization step value 120 (a quantization step code decoded according to the quantization step type), DCT mode information 121, and the like.

The inverse quantization circuit 41 generates a quantization step value 120 for each of the quantization coefficient value data 123 and the macroblock.
Is read out from the parameter memory and subjected to an inverse quantization process, and the DCT coefficient value data 124 is output to the inverse DCT circuit 42. When a user-defined quantization matrix is used in the inverse quantization process, the quantization matrix is also read from the parameter memory.

The inverse DCT circuit 42 performs an inverse DCT process using the DCT coefficient value data 124 and the DCT mode information 121, and outputs difference video data 125 to the motion compensation circuit 43.

The motion compensation circuit 43 has a frame memory for forward prediction and a frame memory for backward prediction, and performs motion compensation processing using the differential video data 125 and the motion vector data 122 to decode the decoded video data. 106 is output to the superimpose circuit 5. Where MPEG
When the frame frequency of the two data is different from the frame frequency used in the reproduction system, the video data 106 decoded by performing the repeat field processing as appropriate is output.

The parameter memory 44 stores the VLD circuit 40
Holds the encoding parameter 105 decoded in the frame unit.

The synchronization generation circuit 45 includes a parameter memory 4
4, the encoding parameters are read out in frame units,
The frame configuration information is output to the superimpose circuit 5 as picture start information 107 indicating the head field on the MPEG2 stream and repeat field information 108 indicating that the playback field is video data generated by the repeat processing.

FIG. 3 shows an example of a repeat field when a movie material having a frame frequency of 24 Hz is reproduced at 480i / 60 of 29.97 Hz. In each field, a top field is denoted by T and a bottom field is denoted by B, and a frame number is represented by a numeral. For example, T0 represents the top field of the 0th frame, and B0 represents the bottom field of the 0th frame. Also,
The elliptical figure indicates the frame position on the MPEG2 stream, and is given a symbol S and a frame number.

The stream S0 has top_field_first =
1, since repeat_field_first = 1, the T1 field is composed of a repeat field of the T0 field. Stream S1 has top_field_first = 0, repeat_
Since field_first = 0, one frame is configured by using B1 which is originally a bottom field as a top field and T2 which is originally a top field as a bottom field. Stream S2 has top_field_first = 0, r
After epeat_field_first = 1, B2 is set to the top field and T3 is set to the bottom field, and then B3 is set to B2.
Play in the repeat field. Similarly, stream S3 has top_field_first = 1, repeat_field_first
= 0, the playback frame is composed of T4 and B4, and the stream S4 is top_field_first = 1, repeat_field_first
After T = 1 and T5 and B5 are reproduced, T6 is reproduced in the repeat field of T5.

As described above, in the 480i / 60, one frame is composed of two fields, a top field and a bottom field, and 29.97 frame images per second. On the other hand, since movie material is composed of 24 still images (frame images) per second, it is necessary to insert approximately 6 frame images per second. The picture start position on the stream is not fixed.

FIG. 4 is a diagram showing output timings of the picture start information 107 and the repeat field information 108 output from the synchronization generation circuit 45. The structure of the MPEG2 stream is the same as that shown in FIG. Picture start information 1
07 is a signal which becomes “H” at the time of the first field on the MPEG2 stream, so that T0, B1, B2, T
4. It becomes "H" at T5. Repeat field information 10
8 is a signal which becomes “H” in the case of a repeat field from the repeat_field_first flag of the MPEG2 parameter.
repeat_field_first flag is "H" at T0, B1, T5
, Indicating that T1, B3, and T6 are each composed of a repeat field.

FIG. 5 is a diagram showing a configuration example of the superimpose circuit 5, in which a character / image generation circuit 50, a delay memory 5
1, frame memory 52, still image determination circuit 53, superimposed area detection circuit 54, adaptive mix circuit 55
It consists of.

The superimpose using the prior art is
In contrast to the character / image generation circuit 50 and the mix circuit corresponding to only a single frame frequency, in the present embodiment, a still image discrimination circuit 53 for judging the generated superimposed image data as a still image / moving image. And the delay memory 5
1; a frame memory 52; and a superimposed area extracting circuit 54. The mixing circuit also performs an adaptive mixing circuit that mixes the video data in consideration of the frame structure of the video data and the superimposed image data and the frame frequency information. 55.

The character / image generation circuit 50 generates characters and image data according to the screen size of the video data 106 to be mixed from the superimposed characters and the image data 104, and the delay memory 51, the still image discrimination circuit 53 Output to the imposed area detection circuit 54. Further, superimposition presence information 131 indicating the presence or absence of superimposition is output to the still image determination circuit 53.

The delay memory 51 has a one-frame memory. The still image discriminating circuit 53 performs frame delay to determine whether the superimposed image is a still image or a moving image. The image is output to the image determination circuit 53, the frame memory 52, and the superimposed area detection circuit 54.

From the superimposed presence information 131, the still image discriminating circuit 53 determines that the superimposed data does not exist, if the superimposed data is invalid, and if the superimposed data is present, the superimposed image data 130 and the superimposed image delayed by the frame are superimposed. The absolute sum of the difference values of the image data 132 is accumulated over one field and compared with a predetermined threshold value. , The superimposed field information 110 and the adaptive mix circuit 55
Is output to the video encoder 6. When the superimposition field information 110 is a moving image, the frame writing control signal 133 for writing the superimposed image data 132 delayed by one frame into the frame memory 52 is stored in the frame memory 52. Output. In the frame in which the still image is switched, the superimposed field information 110 is determined to be a moving image for only one frame, and the superimposed image data 132 with the frame delay is stored in the frame memory 52.
Write.

The frame memory 52 is constituted by a frame memory for one frame, and the frame write control signal 1
When 33 instructs the writing, the superimposed image data 132 delayed by the frame is written into the frame memory, and otherwise, the writing operation is not performed. Further, according to the field readout control signal 134 output from the adaptive mix circuit 55, it outputs top field data or bottom field data recorded in the frame memory.

The superimposed area detection circuit 54
Superimposed image data 132 with frame delay
Detects which coordinates have data, and outputs the coordinate information to the video encoder 6 as a superimposed area identification signal 111.

FIG. 6 shows an example of detecting a superimposed area. The coordinate information may be in pixel units, but since the MPEG2 standard controls video data in macroblock units, the coordinate information is also in macroblock address units, which can reduce the amount of memory required for storing area information. it can. In FIG. 6, the upper left coordinate is (1, 1), and the
In this example, character information is superimposed from a macroblock having coordinates (5, 2) to a macroblock having coordinates (9, 3) on a screen composed of macroblocks and 10 macroblocks in the vertical direction. Are coordinates (5,
2) An identification signal 111 superimposed only in the rectangular area of-(9, 3) is output.

The adaptive mix circuit 55 mixes the decoded video data 106 and the selected superimposed image field data 135 using the picture start information 107, the repeat field information 108, and the superimposed field information 110. And outputs the superimposed video data 109.

FIG. 7 shows an example of a frame memory read control algorithm of the adaptive mix circuit 55. In FIG. 7, S
IF indicates superimposed field information 110, picture start indicates picture start information 107, repeat field indicates repeat field information 108, and field position indicates whether the current field position is a top field or a bottom field. Hereinafter, the algorithm will be described.

Superimpose field information 110
Is a moving image (step S1), the field position to be read from the frame memory is determined from the current field position regardless of the frame structure of the MPEG2 stream (step S5) (steps S5 and S6).

Superimpose field information 110
Is a still image (step S1), the field position to be read is determined based on the encoding information of the MPEG2 stream. First, when the repeat field information 108 is a repeat field (step S3), the video encoder circuit 6 does not superimpose a superimposed image to remove the repeat field, but superimposes the decoded video data 106 as it is. It is output to the video encoder circuit 6 as processed video data 109 (step S9).

If the repeat field information 108 is not a repeat field (step S3), the superimposed image data of the top field and the bottom field is read from the frame memory 52 and decoded according to the picture start information 107 (step S4). And outputs it to the video encoder circuit 6 (steps S7 and S8).

If the superimposed image is not superimposed (step S1), the superimposed image is not superimposed, and the decoded video data 106 is output to the video encoder circuit 6 as the superimposed video data 109 as it is. (Step S9).

FIGS. 8 and 9 show input / output signals of the adaptive mix circuit 55 when the superimposed image is a moving image and a still image, respectively.

As shown in FIG. 8, when the superimposed image is a moving image, regardless of the picture start information 107 and the repeat field information 108 output from the video decoder circuit 4, the frame memory depends on whether the field position is the top field or the bottom field. Field to read from is determined, so if it is the top field,
The superimposed image data of the top field is read from the frame memory, superimposed on the video data 106 decoded by the adaptive mix circuit 55, and the superimposed video data 109 is output to the video encoder circuit 6. You.

FIG. 9 shows that when the superimposed image is a still image, the top field data IT0, IT0,
The superimposed image data that holds the bottom field data IB0 and is read from the frame memory 52 is determined only from the picture start information 107 and the repeat field information 108. Therefore, if the input image is T0
, (T0 + IT0) is output from the repeat field information 108 = “L” and the picture start information 107 = “H”.
From "L" and picture start information 107 = "L" (B0
+ IB0) is output. At T1, the repeat field information = “H”, so that T1 is output as it is. Less than,
In the case of B1, (B1 + IB1) is output, and in the case of T2 (T
2 + IT2).

As described in detail above, by using the superimpose circuit 5 according to the present embodiment, an image having a different frame structure, which cannot be conventionally performed, is superimposed in accordance with the characteristics of the superimposed image data. Since the processing can be performed, it is possible to prevent image quality deterioration when re-encoding by the video encoder 6.

FIG. 10 shows an example of the configuration of the video encoder circuit 6 according to the fifth aspect. The field thinning circuit 60, the adaptive motion vector search circuit 61, the motion compensation circuit 62, the adaptive DCT mode determination circuit 63, DCT circuit 6
4. Adaptive quantization control circuit 65, quantization circuit 66, VLC
(Variable length coding) circuit 67.

The present embodiment is based on Japanese Patent Application 200
In order to make the description example of the specification of 0-197871 correspond to a different frame structure and frame frequency, a circuit configuration other than the field thinning circuit 60 is disclosed in Japanese Patent Application No. 20-214,197.
It has the same configuration as 00-197871.

When the superimposed video data 109 can be subjected to field thinning processing, the field thinning circuit 60 repeats the repeat field information 10 so as to have the same frame order as the MPEG2 video stream 103.
8. A field thinning process is performed using the superimposed field information 110, and the field thinned video data 140 is output to the adaptive motion vector search circuit 61 and the motion compensation circuit 62.

FIG. 11 is a flowchart showing a control example of the field thinning circuit 60. The encoded information in the flowchart represents the decoded MPEG2 encoding parameter 105, and the SIF represents the superimposed field information 110. First, when the input superimposed video data 109 has no encoding information (step S11), since it is not re-encoding, a normal field difference value is obtained (step S12). If it is larger than the threshold value, the field is output (step S16). If it is smaller, the field is thinned because it is the same as the previous field (step S1).
5).

If the coded information 105 is present (step S11), the repeat field information 108 generated from the repeat_field_first flag is a normal image (step S13), or the repeat field and the superimposed field information 110 is a moving image (step S13). S1
4) The field is output (step S18), and if the repeat field information 108 is a repeat field and the superimpose field information 110 does not exist or is a still image (step S14), field thinning is performed (step S17).

When the superimposed image data is a still image, the superimposed image data is not superimposed on the repeat field position when the superimposed image of the present embodiment is used. As shown in FIG. 9, at the output of the video decoder circuit 4, T1 is generated from the field repeat of T0, so that T1 = T0. In the superimposed video data, T0 is (T0 + IT0), T1 is T1,
That is, since it remains at T0, the field thinning circuit 6
Even if the absolute value of the difference value is determined to be 0, field thinning cannot be performed, and the frame configuration of the MPEG2 stream is not obtained.

When the superimposed image data is a moving image, as shown in FIG. 8, T0 is (T0 + IT0) and T1 is
Is (T1 + IT1) = (T0 + IT1), and the field difference value does not become 0. However, since superimposed image data is superimposed at 29.97 Hz, MPEG
If encoding is performed at the frame frequency of two video streams, the data of the superimposed image data is lost.
29. Since flicker occurs and the image quality deteriorates subjectively.
Since encoding is performed at 97 Hz, no field thinning is performed.

As described above, when the frame frequency of the MPEG2 stream is different, it is impossible to re-encode the decoded video data 106 at the frame frequency of the MPEG2 stream by performing some processing on the decoded video data 106 using the conventional field thinning circuit. However, since the superimposing circuit of this embodiment superimposes the video data on the video data in a timely manner according to the characteristics of the image data to be superimposed, the video data of the repeat field can be deleted by the field thinning circuit.

Here, returning to FIG. 10, the configuration will be described. The adaptive motion vector search circuit 80 includes a motion vector search circuit 61
When the prediction source image is in a superimposed area, the video data has been changed by the superimposing process, and the motion vector data 141 searched by the motion vector search circuit 60 is selected. ,
The data is output to the motion compensation circuit 61 as the selected motion vector data. Even when the prediction source image is not in the superimposed area and the current encoded image is in the superimposed area, the moving vector data 141 is selected because the video data has changed.
It outputs to the motion compensation circuit 62 as 42. If the prediction source image is not in the superimposed area and the encoded image is not in the superimposed area, the image data is MPE
MPEG2 stream is no different from MPEG
The motion vector data 122 obtained by decoding the two streams is output to the motion compensation circuit 62 as the selected motion vector data 142.

The motion compensating circuit 62 has a frame memory for storing the prediction source video data.
2, the difference between the video data 140 thinned out by the field and the prediction source video data is obtained.
To the DCT mode determination circuit 63 and the DCT circuit 64. Here, the prediction source video data is obtained by dequantizing and inverse DCT processing the quantized coefficient value data 150 in the local decoding unit in the motion compensation circuit.

The adaptive DCT mode selection circuit 81
It comprises a mode determination circuit 63 and a selection circuit 71.

The DCT mode determination circuit 63 calculates a conversion mode when the field / frame adaptive DCT is used. Generally, in the vertical direction of a luminance signal macro block, a continuous line difference is compared with a difference value for each line, and when the continuous line difference value is smaller, the frame DCT and the difference value for each line are smaller. If it is smaller, the DCT circuit 64 determines that the field DCT
The CT mode information 144 is output.

The selection circuit 71 selects the DCT mode information 121 obtained by decoding the MPEG2 stream and the DCT mode information 144 calculated by the DCT mode determination circuit 63 in accordance with the superimposed area identification signal 111, and selects the selected DCT mode information 145. To the DCT circuit 64.

The DCT circuit 64 generates the difference image data 143
, Using the selected DCT mode information 145 to perform an optimal DCT transform for each macroblock, and output the result to the quantization control circuit 65 and the quantization circuit 66.

The quantization circuit 66 performs a quantization process on the DCT transform coefficient value data 146 using the quantization step value 147, and sends the quantized coefficient value data 1 to the VLC circuit 67.
50 is output.

The VLC circuit 67 stores the quantized coefficient value data 1
50 is encoded using run length and Huffman codes,
Information necessary for encoding such as a picture type and a quantization step value is also added so as to conform to the MPEG2 standard, and the encoded MPEG2 video data 112 is output to the TS encoder 3.

The adaptive quantization control circuit 82 includes a quantization control circuit 65, a non-super area bit number calculation circuit 72, and a selection circuit 73.

The quantization control circuit 65 calculates an optimum quantization step value 147 for each macro block from the activity of the DCT transform coefficient value data 146 and the VLC buffer value 151 indicating the state of the VLC buffer. here,
The quantization determination method is MPEG2 TM4 (Test Model
The method described in 4) is generally used.

The non-super area bit number calculation circuit 72
Using the superimposed area identification signal 111 and the number of encoded bits 126 for each macroblock, the number of bits of the macroblock that is not superimposed in the MPEG2 stream is accumulated for each frame, and The number of encoded bits is output to the selection circuit 73 as 148.

The selection circuit 73 outputs the number of encoded bits 148 in the non-superimposed area, the number of encoded bits 127 for each frame, and the superimposed area identification signal 111.
And the quantization step value 120 obtained by decoding the MPEG2 stream and the quantization step value 147 calculated by the quantization control circuit 65 using the VLC buffer value 151 and the selected quantization step value 149. Output to the quantization circuit 66.

FIG. 12 shows an example of the selection process of the selection circuit 73. First, the number of encoded bits NSPB in the non-superimposed area in the encoded frame (14 in the circuit)
8) and the total number of bits ALLB (127 in the circuit) decoded from the MPEG2 stream are compared (step S21), and (ALLB <NSPB × 2)
If, the quantization step value 147 is selected because the image quality degradation of the superimposed portion may be large (step S24). This is because the image to be superimposed often has characteristics close to a still image, so that if the code amount is about 50% per frame, the code in the superimposed area can be reduced without deteriorating the image quality of the non-superimposed area. This is because conversion can be performed. (ALLB ≧ NS
In the case of (PB × 2), if the state of the VLC buffer is coded with the target code amount or more (step S22), the quantization step value 147 is selected to control with the target code amount (step S24), and the VLC buffer Is encoded with the target code amount or less (step S21), if the current macroblock is in the superimposed area (step S23), the quantization step value 147 is set to (non-superimposed). In the case of the pause area (step S23), the quantization step value 120 decoded from the MPEG2 stream is selected (step S2).
5).

In this embodiment, the hardware configuration has been described. However, with the recent improvement in computer processing capability, even if real-time processing is required, a low-resolution image or non-real-time processing is sufficient. May be configured.

[0074]

According to the re-encoding apparatus and method of the present invention described above, even if the superimposing process is performed on MPEG2 data having different frame frequencies, the image to be superimposed is a still image. Since encoding can be performed at the same frame rate as MPEG2 data, there is an excellent effect that image quality degradation during re-encoding can be minimized.

[Brief description of the drawings]

FIG. 1 is an overall block diagram of a re-encoding device.

FIG. 2 is a block diagram of a video decoder circuit.

FIG. 3 is a diagram showing an example of expanding an MPEG2 stream recorded at 24 Hz to 29.97 Hz;

FIG. 4 is a diagram illustrating an example of a timing of an output signal of a synchronization generation circuit.

FIG. 5 is a block diagram of an adaptive superimpose circuit.

FIG. 6 is a diagram showing an example of a superimposed area.

FIG. 7 is a flowchart showing frame memory read control of the adaptive mix circuit.

FIG. 8 is a diagram illustrating an example of a data mix when superimposed data is a moving image;

FIG. 9 is a diagram showing an example of a data mix when the superimposed data is a still image

FIG. 10 is a flowchart illustrating a method of controlling field thinning.

FIG. 11 is a flowchart illustrating a method of controlling field thinning.

FIG. 12 is a flowchart illustrating a control method of the adaptive quantization control circuit.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 TS decoder 2 audio delay memory 3 TS encoder 4 video decoder 5 superimpose circuit 6 video encoder 40 VLD circuit 41 inverse quantization circuit 42 inverse DCT circuit 43 motion compensation circuit 44 parameter memory 45 synchronization generation circuit 50 character / image generation circuit Reference Signs List 51 delay memory 52 frame memory 53 still image discrimination circuit 54 superimposed area detection circuit 55 adaptive mix circuit 60 field thinning circuit 61 motion vector search circuit 62 motion compensation circuit 63 DCT mode determination circuit 64 DCT circuit 65 quantization control circuit 66 quantum Conversion circuit 67 VLC circuit 70 selection circuit 71 selection circuit 72 non-super area bit number calculation circuit 73 selection circuit 80 adaptive motion vector search circuit 81 adaptive DCT mode search circuit 82 adaptive quantization control circuit 1 0 MPEG2-TS stream 101 Audio stream 102 Delayed audio stream 103 MPEG2 video stream 104 Superimposed characters and image data 105 Coding parameters of decoded MPEG2 stream 106 Decoded video data 107 Picture start information 108 Repeat field information 109 Superimposed video data 110 Superimposed field information 111 Superimposed area information 112 Encoded MPEG2 video stream 113 Recoded MPEG2-TS stream 120 Quantization step value 121 DCT mode 122 Motion vector data 123 Quantized coefficient value data 124 DCT coefficient value data 125 Difference video data 126 Macrob Number of coded bits per lock 127 Number of coded bits per frame 130 Superimposed image data 131 Superimposed presence information 132 Superimposed image data delayed by 133 frames Write control signal 134 Field read control signal 135 Selected Superimposed image field data 140 Field thinned video data 141 Motion vector data 142 Selected motion vector data 143 Difference video data 144 DCT mode 145 Selected DCT mode 146 DCT transform coefficient value 147 Quantization step value 148 Non Number of coding bits in superimposed area 149 Selected quantization step value 150 Quantization coefficient value data 151 VLC buffer value

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Claims (10)

[Claims] 1. A video decoder for acquiring an encoding parameter of an MPEG2 video stream for each picture, and outputting a decoded encoding parameter in synchronization with a decoded reproduced video signal, and transmitting a character information or image information to the reproduced video signal. And a video encoder for re-encoding the superimposed video signal to MPEG2. The video decoder refers to the repeat information of the next field in the picture header, which is an MPEG2 encoding parameter. A function of outputting picture start information and repeat field information of an MPEG2 stream in synchronization with the reproduced video signal, wherein the superimposing means detects a superimposed area and outputs the superimposed video signal to the superimposed video signal. Sue detected synchronously Recoding apparatus having a superimpose function, characterized in that it comprises a superimposing area detection means for outputting Inpozu area information. 2. The re-encoding device according to claim 1, wherein the superimposing means determines whether the image to be superimposed is a still image or a moving image, and detects the image in synchronization with the superimposed video signal. A re-encoding device comprising superimposed image still image discriminating means for outputting the obtained superimposed still image discrimination information. 3. The re-encoding device according to claim 2, wherein said superimposing means determines that said superimposed image still image discriminating means is a still image.
A re-encoding method comprising: superimposing a superimposed image according to the field structure information and the repeat field information of an MPEG2 stream; and superimposing a superimposed image according to a preset field structure when a moving image is determined. apparatus. 4. The re-encoding device according to claim 2, wherein, when the superimposed area information does not exist, the video encoder reuses an encoding parameter acquired by the video decoder circuit to perform MPEG2 encoding. When the superimposed area information is present and the frame frequency information in the encoding parameter is different from a preset frame frequency, the MPEG2 encoding is performed at the set frame frequency without reusing the encoding parameter. A re-encoding device. 5. The re-encoding device according to claim 3, wherein, when the superimposed area information does not exist, the video encoder reuses the encoding parameters acquired by the video decoder to perform MPEG2 encoding. When the superimposed area information exists and the superimposed still image discrimination information is a still image,
At the frame frequency of the MPEG2 stream, MPEG2 encoding is performed by reusing the encoding parameters obtained from the video decoder, and the superimposed area information exists and the superimposed still image discrimination information is a moving image. A re-encoding apparatus characterized in that, when the frame frequency information in the encoding parameter differs from a preset frame frequency, MPEG2 encoding is performed at the set frame frequency without reusing the encoding parameter. 6. An MPEG2 decoding process for acquiring an encoding parameter of an MPEG2 video stream for each picture and outputting a decoded encoding parameter in synchronization with a decoded reproduced video signal, and converting character information or image information to the reproduced video signal. A superimpose process for superimposing on a signal and a superimposed video signal
A re-encoding method having a superimpose function including an MPEG2 encoding process for encoding, wherein the MPEG2 decoding process refers to repeat information of a next field in a picture header which is an MPEG2 encoding parameter, MPEG synchronized with the playback video signal
A superimposition process including a function of outputting picture start information and repeat field information of two streams, wherein the superimposing process detects a superimposed region and detects the superimposed region in synchronization with the superimposed video signal. A re-encoding method including a superimposed area detection process for outputting information. 7. The re-encoding method according to claim 6, wherein the superimposing process determines whether a superimposed image is a still image or a moving image, and detects the image in synchronization with the superimposed video signal. A re-encoding method comprising superimposed image still image discrimination processing for outputting the obtained superimposed still image discrimination information. 8. The re-encoding method according to claim 7, wherein in the superimposing process, when the superimposed image still image discriminating process determines that the image is a still image, the field structure information of the MPEG2 stream is used. And superimposing a superimposed image according to the repeat field information and superimposing the superimposed image according to a preset field structure when it is determined that the image is a moving image. 9. The re-encoding method according to claim 7, wherein in the MPEG2 encoding process, when the superimposed area information does not exist, an MPEG2 encoding process is performed by reusing encoding parameters obtained in the MPEG2 decoding process. If the superimposed area information is present and the frame frequency information in the encoding parameter is different from the preset frame frequency, the MPEG2 encoding is performed at the set frame frequency without reusing the encoding parameter. A re-encoding method. 10. The re-encoding method according to claim 8, wherein in the MPEG-2 encoding process, when the superimposition area information does not exist, the MPEG-2 encoding process is performed by reusing encoding parameters obtained in the MPEG-2 decoding process. When the superimposed area information exists and the superimposed still image discrimination information is a still image,
At the frame frequency of the MPEG2 stream,
MPEG2 encoding is performed by reusing the encoding parameters obtained from the PEG2 decoding processing. When the superimposed area information exists and the superimposed still image discrimination information is a moving image, the Wherein the frame frequency information is different from a preset frame frequency, the MPEG2 encoding is performed at the set frame frequency without reusing the encoding parameters.