JP3125923B2 - Moving image recording apparatus and transfer rate control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION In an apparatus for recording moving image information such as television broadcasts on a recording medium which can be recorded and reproduced at any time, recording and reproduction are performed particularly at a variable transfer rate, and an inputted moving image signal can be efficiently recorded. The present invention relates to a moving image recording apparatus that controls a transfer rate when encoding.

[0002]

2. Description of the Related Art <Moving picture recording apparatus and transfer rate control method> In a moving picture high-efficiency coding which performs an inter-picture prediction process represented by MPEG or the like, a generated code amount greatly varies depending on an image portion. Therefore, the generated code amount is controlled according to the purpose. When the recording medium has a fixed transfer rate, the encoding is also performed at the fixed transfer rate. Specifically, 0.2
It has an output code buffer with an average generated code amount of about seconds,
The quantization step is controlled according to the buffer sufficiency so that the buffer does not overflow or underflow. In this case, in the part where the generated code amount is originally large,
The quantization is controlled to be coarse, and the image quality is reduced. Therefore, it is necessary to set the transfer rate to such a high level that the image quality does not matter.

On the other hand, a recording medium such as a DVD (Digital Video Disc) whose reproduction transfer rate can be changed at any time can be encoded at a variable transfer rate. However,
Since the total generated capacity needs to be adjusted to the medium capacity, the necessary code amount of each part of the image is first determined by tentative coding, and then the distribution code amount of each part is determined. The main encoding is performed while controlling so as to match the distribution code amount. The specific method is described in Japanese Patent Application Laid-Open No. 6-141298, entitled "Variable Transfer Rate Coding Apparatus and Recording Medium" by the same applicant as the present application. This method enables recording in which both the total capacity and the partial code amount are ideal for a read-only medium.
Since it is necessary to perform encoding, it cannot be used when an incoming moving image is encoded and recorded as needed. In a device that records moving images at any time, it is necessary to clarify the recordable time for each medium, so that control similar to a fixed transfer rate is performed even with a variable transfer rate. Specifically, it is assumed that the capacity of the output code buffer, which was about 0.2 seconds at a normal fixed transfer rate, is increased to about 200 seconds.
Then, since the generated code amount variation within the range is allowed, the average transfer rate is reduced.

In this case, since the code amount of the buffer is uncertain, it is necessary to have a margin for the code amount, which results in a loss of recording time. However, if the total recording time is 3 hours, the loss is about 2%, and the effect of reducing the average rate by the variable transfer is greater. Note that the buffer does not actually have the capacity, but becomes a virtual buffer for encoding control. The fluctuation of the generated code amount is absorbed not by the buffer but by the recording / reproducing system.

<Moving Image Recording Apparatus> One configuration example of a conventional moving image recording apparatus will be described below. FIG. 6 shows the configuration. The moving image signal input from the image signal input terminal 1 is converted into a code string by the moving image encoder 2 and is supplied to the recording circuit 3 and the virtual buffer 61. The moving picture encoder 2 performs high-efficiency moving picture coding such as the MPEG-2 system. The virtual buffer 61 receives an incoming code string,
Information on the buffer sufficiency in the buffer operation is given to the quantization controller 7. The quantization controller 7 sets a quantization step according to the information on the buffer sufficiency, and supplies the value to the video encoder 2. The moving image encoder 2 performs quantization of an incoming code sequence based on a given quantization step.

On the other hand, the recording circuit 3 subjects the code sequence to digital recording signal processing such as error correction code addition and EFM modulation, and supplies the obtained recording signal to the pickup 9. The pickup 9 records a moving image signal for recording on a recording medium 12 such as a disk, and reads the moving image signal from the recording medium 12. Recording or reproduction on the recording medium 12 is performed at the track position set by the recording position controller 62. The recording position controller 62 grasps the unrecorded area or the recordable area from the recording operation up to that time and the recorded contents table (TOC) of the recording medium 12, and controls the pickup 9 so as to sequentially record there.

[0007] The recording medium 12 is a recordable optical disk or the like having a capacity of about 10 Gbytes. Assuming that the average transfer rate of the code string is 7 Mbps, a moving image of 3 hours can be recorded. Next, during reproduction, a reproduction signal read by the pickup 9 from the recording medium 12 is supplied to the reproduction circuit 4. The reproduction circuit 4 performs the reverse processing of the recording circuit 3, reproduces a moving image code string from the read signal, and supplies the reproduced signal to the moving image decoder 5. In the moving picture decoder 5, the inverse processing of the moving picture encoder 2 is performed, and the obtained reproduced picture signal is output from the picture output terminal 6.

<Rate Control Method> A basic method of rate control by feedback using a virtual buffer will be described. When the generated code amount is large in the video encoder 2 and the code is accumulated in the virtual buffer 61, the quantization step is coarsened by the quantization controller 7, the generated code amount is suppressed, and conversely, the generated code amount is small. When the virtual buffer becomes empty, the quantization step is made finer, and the generated code amount is increased.

The specific operation of the rate control method is as follows. In the virtual buffer 61, the difference between the target average code amount (rate) and the actual code amount (rate) is obtained. In the virtual buffer 61, the code amount is observed at any time from the incoming code,
Assuming that the code amount of the preset target transfer rate is read, the accumulated value of the difference is obtained as the code amount remaining in the virtual buffer. The residual code amount is normalized by the capacity of the buffer, becomes the buffer sufficiency of what percentage of the data is stored in the virtual buffer, and is output. In the case of MPEG or the like, since the buffer capacity is constant, the transfer rate is normalized by a reaction coefficient obtained by multiplying the transfer rate by a constant.

The quantization controller 7 sets a quantization step according to the buffer sufficiency. FIG. 5 shows the setting characteristics. When the generated code amount is larger than the target and the buffer sufficiency is high, the quantization step is increased to suppress the generated code amount. Conversely, when the generated code amount is smaller than the target and the buffer sufficiency is low, the quantization step is reduced and the generated code amount is increased. In MPEG,
Since the amount of generated codes greatly differs depending on the image prediction structure (picture type), a deviation from a target rate set for each picture is used instead of a mere buffer sufficiency.

[0011]

According to the conventional variable transfer rate control method for occasional recording, when the capacity of the virtual buffer is increased, the degree of freedom of the transfer rate increases and the average transfer rate can be reduced. The code amount error increases,
The recordable time is wasted. On the other hand, when the virtual buffer capacity is reduced, the operation becomes close to the fixed transfer rate, and the coding efficiency also becomes close to the fixed transfer rate. The present invention has been made by paying attention to the above points, and a moving image variable in which the virtual buffer capacity is set according to the remaining recording capacity, the buffer capacity is reduced as the remaining capacity decreases, and the target average transfer rate is increased. It is an object to provide a transfer rate control method.

[0012]

SUMMARY OF THE INVENTION According to the present invention, when a moving image signal is encoded at a variable transfer rate and recorded on a recording medium having a predetermined total recording capacity, the total recordable code amount of the recording medium and the recording amount are recorded. According to the remaining capacity obtained from the completed code amount, the capacity of the virtual buffer used in the transfer rate control is set, and the quantization step is obtained according to the degree of sufficiency of the virtual buffer of the capacity, and based on the quantization step, A moving image recording apparatus that encodes a moving image and a transfer rate control method. Also,
A moving image recording apparatus for setting a target average transfer rate read from a virtual buffer according to a remaining capacity and a transfer rate control method.

(Operation) In the moving image recording / reproducing apparatus of the present invention, the virtual buffer capacity is set in accordance with the remaining recording capacity in the transfer rate control for occasional recording, and the virtual buffer is large when the remaining capacity is large. In this case, the feedback control is gradual, and the generated code amount is almost free. Since the virtual buffer is made smaller and the target average rate is increased as the remaining capacity decreases, the operation approaches that of a normal fixed transfer rate. Since the virtual buffer capacity at the end is equal to that of the fixed transfer rate, the deviation of the generated code amount from the target becomes small. Since the target average rate according to the virtual buffer capacity is given, the balance of the image quality is also appropriate.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Moving Image Recording Apparatus One embodiment of the moving image recording apparatus of the present invention will be described below.
FIG. 1 shows the configuration, and the same components as those in the conventional example of FIG. 6 are denoted by the same reference numerals. FIG. 1 shows a virtual buffer controller 10 not shown in FIG. Also,
The operations of the virtual buffer 8 and the recording position controller 10 are different from those of the virtual buffer 61 and the recording position controller 62 in FIG.

A moving image signal input from an image signal input terminal 1 is converted into a code string by a moving image encoder 2 and is supplied to a recording circuit 3 and a virtual buffer 8. The moving image encoder 2 has MP
It performs high-efficiency moving picture coding such as the EG-2 method. Encoding is performed at a variable transfer rate, and the generated code amount changes as needed. The virtual buffer 8 calculates from the incoming code sequence
A buffer sufficiency corresponding to the average target transfer rate and the virtual buffer capacity is obtained, and information on the buffer sufficiency is given to the quantization controller. The average target transfer rate and the virtual buffer capacity in the virtual buffer 8 are set as needed based on setting information provided from the buffer controller 10. This operation is a feature of the present invention and will be described later in detail.

The buffer controller 10 includes a recording position controller 1
The average target transfer rate and the virtual buffer capacity are set and output based on the remaining recording capacity given from No. 1. The recording position controller 11 grasps the unrecorded area or the recordable area from the total capacity of the recording medium 12 and the recording operation up to that time and the recording contents table (TOC) of the recording medium 12, calculates the remaining capacity, and outputs the remaining capacity. .
The quantization controller 7 sets a quantization step according to the information on the buffer sufficiency, and supplies the value to the video encoder 2. FIG. 5 shows an example of the quantization step for the buffer sufficiency.
Shown in The moving image encoder 2 performs quantization based on a quantization step given according to the buffer sufficiency. On the other hand, the recording circuit 3 performs signal processing for digital recording such as addition of an error correction code or EFM modulation on the code sequence, and supplies the obtained recording signal to the pickup 9.

The pickup 9 records and reads a moving image signal for recording on a recording medium 12. Medium 1
Recording and reproduction to and from the track 2 are performed at the track position set by the recording position controller 11. Here, the incoming signal has a variable transfer rate, while the signal recording speed is constant, so that the signal is intermittently recorded according to the rate. When the rate is high, recording is performed continuously, but when the rate is low, a gap is opened. The recording position controller 11 controls the pickup 9 so as to sequentially record data in an unrecorded area (recordable area). Recording medium 12
Is a recordable optical disk or the like having a capacity of about 10 Gbytes. With a variable transfer rate with a high degree of freedom,
The average transfer is set lower than in the conventional example, and if the average transfer rate is 4 Mbps, recording for 5 hours is possible.

Next, the operation at the time of reproduction will be described. In FIG. 1, a signal read by a pickup 9 is given to a reproducing circuit 5. Since the signal recorded here has a variable transfer rate and a constant signal reading speed, it is read intermittently according to the rate. When the rate is high, reading is performed continuously, but when the rate is low, a gap is opened. The reproducing circuit 4 performs the reverse process of the recording circuit 3, reproduces a moving image code string from the read signal, and supplies the reproduced signal to the moving image decoder 5. In the moving picture decoder 5, the inverse processing of the moving picture encoder 2 is performed, and the obtained reproduced picture signal is output from the picture output terminal 6.

<Operation of Virtual Buffer> FIG. 2 shows an embodiment of the internal structure of the present invention shown in FIG. 1, and the operation of the virtual buffer 8 which is a feature of the present invention will be described below. FIG.
As shown in the figure, the virtual buffer 8
1, a subtractor 22, an accumulator 23, a normalizer 24, a target average transfer rate memory 25, and a virtual buffer capacity memory 26.

The code sequence coming from the video encoder 2 is
The code amount per predetermined unit time such as one frame is counted by the code counter 21, and is supplied to the subtracter 22. Subtractor 22
Then, the target code amount per predetermined unit time determined by the target average rate given from the target average transfer rate memory 25 is subtracted. The result of the subtraction is accumulated by the accumulator 23 and becomes the residual code amount of the virtual buffer 8. The initial value of the residual code amount is generally set to the median value of the buffer capacity, but is set to 0 in the present invention because the buffer capacity is changed. In this case, if the generated code amount is smaller than the target, the residual code amount becomes a negative value, but there is no inconvenience due to the virtual buffer.

The virtual buffer residual code amount is calculated by a normalizer 24.
Is divided by the virtual buffer capacity given from the virtual buffer capacity memory 26 and output as a normalized virtual buffer sufficiency. Since the present invention is a variable transfer rate, when the generated code amount is lower than the target value, it is not necessary to forcibly increase the generated code amount. Therefore, when the sufficiency is negative, the value of the virtual buffer may be divided as a larger value. Here, the target average transfer rate and the virtual buffer capacity are given from the buffer controller 10 as parameters, and are updated until the target average transfer rate memory 2 is updated.
5 and the virtual buffer capacity memory 26.

<Setting of Capacity of Virtual Buffer> Setting of capacity of a virtual buffer, which is a feature of the present invention, will be described.
The capacity of the virtual buffer is proportional to the remaining capacity of the recording medium as shown in FIG. 3, and the specific capacity is about half of the remaining capacity. This capacity is extremely large as a virtual buffer for encoding control, and the effect of feedback control is small unless a deviation from the target code amount is accumulated for a very long time. In most cases, the average quantization value is maintained, resulting in ideal variable transfer rate coding.

Since the capacity of the virtual buffer is proportional to the remaining capacity of the recording medium 12, a predetermined remaining recording capacity is always secured for the remaining recording time unless the virtual buffer overflows or underflows. The degree is determined by the degree of sufficiency of the virtual buffer. When the virtual buffer is set to A times the remaining capacity of the recording medium, the following is obtained. First, when the sufficiency is 0, the generated code amount is as planned, and there remains a recording capacity that can be encoded at a preset target average rate thereafter. Assuming that the generated code amount is smaller than the target value and the sufficiency becomes -0.5 (virtual buffer is empty), coding is thereafter performed at an average (1 + A / 2) rate. Conversely, if the sufficiency is +0.5 (virtual buffer is full), then encoding is performed at an average rate of (1-A / 2).

This value always holds irrespective of the recording position (remaining capacity), and the effect on the encoding rate thereafter is always equal. Here, as the ratio of the virtual buffer capacity A to the remaining recording capacity is increased, the degree of freedom of the rate change is increased and the effect of the variable transfer rate can be increased. The risk of improper rates increases. From these balances, the specific value of A is set to about 0.5.

Next, a change accompanying a change in the recording position (remaining capacity) will be described below. As moving image information is recorded on the medium, the remaining capacity decreases, and the virtual buffer capacity also decreases. The control becomes gradually easier according to this, but the action is moderate. Even if the remaining capacity becomes about 10%, it is still a very large virtual buffer of 500 MByte, and the variable transfer rate operation is performed. The operation near the normal fixed transfer rate is performed only at the very end. Since it is inconvenient for the virtual buffer to be completely zero at the end, the virtual buffer used at the normal fixed transfer rate (20
About 0 kByte) is left.

<Setting of Target Average Rate> If the virtual buffer capacity decreases as the remaining capacity decreases and control becomes easier, coarse quantization is more likely to be performed in places where the generated code amount is large. In this case, if the average transfer rate is the same,
Image quality degradation occurs. Therefore, the average target transfer rate is increased as the number of virtual buffers decreases. This degree is set based on the relationship between the degree of freedom of the transfer rate statistically obtained in advance and the required average transfer rate. However, the degree of remarkable increase is when the remaining capacity becomes extremely small.

FIG. 4 shows the target average transfer rate and the actual transfer rate according to the present invention. The actual transfer rate shown by the solid line is
Following the target average transfer rate indicated by the dotted line, the degree of rate fluctuation is suppressed as the remaining capacity decreases.

[0028]

According to the moving picture recording / reproducing apparatus of the present invention, the virtual buffer is set to a large value when the remaining capacity is large according to the remaining recording capacity. Make full use of the transfer rate. Since the virtual buffer is made smaller and the average rate is increased as the remaining capacity becomes smaller, the operation approaches the fixed transfer rate, and recording can be performed without failure and without loss to the end of the medium. Since the degree of freedom of the variable transfer rate is increased at portions other than the end portion, it is possible to lower the average transfer rate, and it is possible to record for a longer time with the same image quality. Since the variation of the quantization step is small, the uniformity of the image quality is improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of a moving image recording apparatus according to the present invention.

FIG. 2 is a diagram showing a configuration of an embodiment of a virtual buffer of the moving image recording apparatus of the present invention.

FIG. 3 is a diagram illustrating a state of a virtual buffer capacity with respect to a remaining capacity according to the present invention.

FIG. 4 is a diagram showing a state of a target average transfer rate and an actual transfer rate according to the present invention.

FIG. 5 is a diagram illustrating a relationship between a buffer sufficiency and a quantization step according to the present invention.

FIG. 6 is a diagram illustrating a configuration example of a conventional moving image recording apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image input terminal 2 Video encoder 3 Recording circuit 4 Reproduction circuit 5 Video decoder 6 Image output terminal 7 Quantization controller 8, 61 Virtual buffer 9 Pickup 10 Buffer controller 11, 62 Recording position controller 12 Recording medium 21 Code counter 22 Subtractor 23 Cumulative adder 24 Normalizer 25 Average target rate memory 26 Virtual buffer capacity memory

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N 5/91-5/956 H04N 7/24

Claims (4)

(57) [Claims] 1. A moving image recording apparatus which encodes a moving image signal at a variable transfer rate and records the same on a recording medium having a predetermined total recording capacity, comprising: A remaining capacity calculating unit that obtains a remaining capacity; a virtual buffer setting unit that outputs information on a capacity of a virtual buffer used in transfer rate control according to the remaining capacity; and a capacity is set based on the information on the capacity of the virtual buffer. Virtual buffer means for outputting sufficiency information of the virtual buffer; quantization step control means for setting a quantization step according to the sufficiency information; and a moving picture code for coding a moving picture based on the quantization step. A moving image recording apparatus, comprising: 2. The moving image recording apparatus according to claim 1, wherein the virtual buffer setting unit outputs information on a target average transfer rate read from the virtual buffer according to the remaining capacity. A moving image recording apparatus, wherein a transfer rate read from the virtual buffer is set based on information on a target average transfer rate. 3. A transfer rate control method when a moving image signal is encoded at a variable transfer rate and recorded on a recording medium having a predetermined total recording capacity, wherein a recordable total code amount of the recording medium and a recorded code are recorded. Obtain the remaining capacity from the amount, output the information on the capacity of the virtual buffer used in the transfer rate control according to the remaining capacity, and calculate the sufficiency information of the virtual buffer whose capacity is set by the information on the capacity of the virtual buffer. Outputting a quantization step according to the sufficiency information, and encoding a moving image based on the quantization step. 4. The transfer rate control method according to claim 3, wherein information on a target average transfer rate read from the virtual buffer according to the remaining capacity is output, and the information is read from the virtual buffer with the information on the target average transfer rate. A transfer rate control method, wherein a transfer rate is set.