JPH0879702A - Data reproducing method and data reproducing device - Google Patents

Abstract

PURPOSE: To quickly provide a display image at the time of special production. CONSTITUTION: When a GOP decoded in a decoder 6 at present is a GOP.0, at the time of being operated to a standstill mode, the GOP.0 and a GOP.-1 which is the one before the GOP.0 are read from a disk and written in a buffer 5. Then, when a frame reverse feed button is operated, by sending the data of the GOPs written in the buffer 5 to the decoder 6, video signals at the time of reverse reproduction are immediately obtained from the decoder 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a data reproducing method and a data reproducing apparatus suitable for reproducing data such as video or audio recorded on an optical disk, a magneto-optical disk, etc. It is suitable for special reproduction.

[0002]

2. Description of the Related Art Digital video discs (hereinafter referred to as
It is written as DVD. ) As a method for compressing and encoding a digital image signal recorded in
icturecoding Experts Group) system has been proposed, and an example of an MPEG encoder will be described with reference to FIG. The MPEG encoder is an encoder that performs compression by predictive encoding, and the digitized image input signal is divided into blocks in the motion detection circuit 101 for each minimum unit block (MB) of motion compensation prediction. Has been
Motion vector detection for motion compensation prediction is performed for each block.

This block is predictively coded in the subsequent predictive coding unit. (1) The DCT is directly applied to the image input signal.
(Discrete Cosine Transform): Intra block that performs (discrete cosine transform), (2) forward block that predicts only from the forward direction, (3) backward block that predicts only from the backward direction, and (4) bi-predictive block that predicts from both directions. Classified into one.

That is, a kind of Fourier transform DCT is performed in the DCT 103, and the resulting DCT coefficient is quantized in the quantization circuit 104. further,
After being quantized, the variable length coding means 109 assigns codes of different lengths according to the occurrence probabilities to perform variable length coding. Further, the quantized signal is inversely quantized by the inverse quantization circuit 105, further inversely DCTed by the inverse DCT 106, and the output from the frame memory predictor 108 is added to reproduce the original image signal. To be done. The reproduced image signal is supplied to the subtractor 102 as a prediction signal.

The predictive coded signal output from the variable length coding means 109 is multiplexed with the prediction mode information and the motion vector signal in the multiplexing means 110, and the information obtained by multiplexing these is generated at an irregular rate. Therefore, the buffer 111 is temporarily stored and is output with a constant coding rate. In order to keep the average of the coding rates constant, the code amount control may be performed by changing the quantization scale factor q of the quantizing means 104 according to the code amount accumulated in the buffer 111. .

FIG. 6A shows the structure of inter-frame prediction thus predictively coded. In this figure, 1
The GOP is composed of, for example, 9 frames, and the I picture is 1 frame, the P picture is 2 frames, and the remaining 6 frames are B pictures to form 1 GOP.
This I picture is an intra-frame predictive-encoded encoded image, and the P picture is an already-encoded temporally previous frame (I picture or P picture) that is predicted from an inter-frame predictive encoded. Image, B
A picture is an inter-frame predictive-encoded image that is already encoded and is predicted from two temporally preceding and following frames.

That is, as shown by the arrow, the I picture is predictively coded only within that frame, and P
The picture P ₀ is interframe predictive coded with reference to the I picture I ₀ , and the P picture P ₁ is the P picture P _0.
And referring to the inter-frame prediction coding with the, B-pictures B _0, B ₁ is 2 and I-picture I ₀ and P picture P ₀
B pictures B ₂ and B ₃ are interframe predictive coded with reference to two pictures, P picture P ₀ and P picture P ₁ . Similarly, the following pictures are created by predictive coding.

By the way, in order to decode a picture that has been predictively coded in this way, since an I picture is coded by intraframe predictive coding, it is possible to decode only an I picture, but P A picture needs to refer to a temporally previous I picture or P picture at the time of decoding, and a B picture needs to refer to previous or next I picture or B picture at the time of decoding. Therefore, the pictures are replaced as shown in FIG. 6B so that the required reference pictures can be decoded in advance.

[0009] As shown in this replacement FIG, B-pictures B _-1, B _-2 since it requires the I-picture I ₀ is the time of decoding, B-pictures B _-1, I picture I ₀ from B _-2 prior As described above, since the B pictures B ₀ and B ₁ require the I picture I ₀ and the P picture P ₀ at the time of decoding, the B picture B ₀ and B ₁ are similarly preceded by the P picture P _{0. 2} and B ₃ are P pictures P when decoding
B picture B because ₀ and P picture P ₁ are required
_Since B picture B ₄ and B ₅ require P picture P ₁ and I picture I ₁ at the time of decoding so that P picture P ₁ precedes ₂ and B ₃ , I picture is more important than B picture B ₄ and B _5.
The picture I ₁ has been swapped so that it precedes.

I-pictures, P-pictures and B-pictures are recorded on the DVD in the order shown in FIG. 6B. Since these pictures are predictively coded as described above, their codes are The amount is not constant and varies depending on the correlation ratio and the image. Therefore, when recording these pictures on the DVD, the sectors are defined by a certain amount of codes. A mode of recording by this sector is shown in FIG. 7. For example, the I picture I ₀ has a sector m, a sector (m + 1) and a sector (m +).
The B picture B _-2 is recorded in a part of the area 2), and the B picture B _-2 is recorded in the area where the sector (m + 2) remains and the sector (m + 3). The data is sequentially recorded in a plurality of sectors, and 1G in this example.
The OP is recorded in the sectors m to (m + 13). However, 1 GOP is not always recorded with such a number of sectors, and since the code amount differs depending on the complexity and flatness of the image, the number of sectors in which 1 GOP is recorded also differs.

[0011]

However, when special reproduction such as reverse reproduction is attempted while reproducing the data recorded on the DVD in the order shown in FIG. 6 (b), the screen is not displayed. It takes some time until the displayed video signal is output. There is a problem that the user feels uncomfortable if the screen such as reverse does not start to be displayed until a certain period of time elapses after the operation button is pressed. The reason why the special playback is delayed will be explained by using the backward playback as an example. To decode the video signal displayed on the screen when the backward playback is performed, the GOP data immediately preceding by time is picked up. This is because it takes time to read from the DVD and it also takes time to decode the video signal of each frame that constitutes the read GOP.

Next, the reason why it takes time to decode backward reproduction will be described. Assuming that the GOP immediately preceding the current GOP is composed of the I picture I ₀ to B picture B ₅ in the order shown in FIG. 6A, the I picture of the current GOP at the time of backward reproduction. After the video of I ₁ ,
The picture of B picture B ₅ is displayed, followed by B picture B
₄ , P picture P ₁ , B picture B ₃ , B picture B
₂ , P picture P ₀ , B picture B ₁ , B picture B
_The video must be displayed in the order of ₀ and I picture I ₀ .

However, B picture B ₅ , B picture B
₄ is necessary data from those predicted based on the I-picture I ₁ and P picture P _1, and I-picture I ₁ and P picture P ₁ when decoding Nevertheless, P picture P ₁ has been predicted with reference to P picture P _0, further P-picture P ₀ is I-picture I
_Since it was predicted with reference to ₀ , after all, I picture I ₀ was decoded, P picture P ₀ was decoded by referring to this, and further P picture P was obtained by referring to this. Must decode ₁ . Then, with reference to the I picture I ₁ and the decoded P picture P ₁ , B picture B ₅ , B picture B
_{Since 4} has to be decoded, time is spent decoding.

Therefore, it is an object of the present invention to provide a data reproducing method and a data reproducing apparatus which can perform special reproduction quickly even during special reproduction such as reverse reproduction.

[0015]

In order to achieve the above object, a data reproducing method of the present invention reproduces an image signal by demodulating data read by a pickup from a disc and decoding it through a buffer. In the data reproducing method described above, the buffer has a capacity capable of storing at least 2 GOPs each composed of a plurality of frames, and when the still mode is instructed, the GOP immediately preceding the GOP being decoded in time. Reading at least 1 GOP of data from the disk,
By storing in the buffer, the special reproduction mode is prepared. Further, in the data reproducing method, the special reproduction mode is the reverse reproduction mode.

Further, the data reproducing apparatus of the present invention which achieves the above object, includes a demodulating means for demodulating the data read by the pickup from the disc, a buffer for temporarily storing the demodulated data, and a read from the buffer. In a data reproducing device including a decoder for decoding the generated data into an image signal, the buffer has a capacity capable of storing at least 2 GOPs of GOPs composed of a plurality of frames, and when a still mode is instructed, At least 1 GOP of data including a GOP immediately preceding the GOP being decoded by the decoder is read from the disk and stored in the buffer to prepare for the special reproduction mode. Further, in the data reproducing apparatus, the special reproduction mode is set to the reverse reproduction mode.

[0017]

According to the present invention, in general, after the still mode is selected, the special reproduction mode such as the reverse reproduction mode is often used. Therefore, when the still mode is instructed, the previous GOP is read. With this setting, since the previous GOP has already been read when the special reproduction mode is instructed, the special reproduction screen can be displayed quickly. Further, when the buffer capacity is sufficiently large, a plurality of GOs before and after the GOP including the video being output are displayed.
By rewriting the inside of the buffer with P, it becomes possible to quickly cope with frame advance and variable speed reproduction not only in the reverse direction but also in the forward direction. As described above, the present invention reduces the number of disk accesses by always storing a little past data in the buffer, and further shifts from the normal playback to the special playback mode quickly only by controlling the buffer. You will be able to.

[0018]

1 is a system diagram of a data reproducing apparatus according to an embodiment of the present invention. In this figure, 1 is MPEG for digital video data, digital audio data, etc.
A disc (DVD) that is compressed and recorded by means such as 2 is a pickup that reads the digital data recorded from the disc 1, 3 is a demodulation circuit that demodulates the read digital data, and 4 is an error that uses an error correction code An error correction circuit (ECC) 5 for correcting is a buffer inserted to buffer a rate on the decoder side different from a rate on the read side, and 6 is an image signal displayed on a display device with encoded data. Decode and output (VIDEO OU
T) decoder.

Further, 7 is a system control that sends various control signals to the servo circuit 9 to perform focus control, tracking control, sled control, etc., 8 is a play button, stop button, double speed play, reverse play button operated by the user. Operation keys such as 9 are the focus control, the tracking control of the pickup 2 under the control of the system control 7,
This is a servo circuit that performs thread control and the like.

The operation of the data reproducing apparatus thus configured will be described. The disc 1 is rotationally controlled by a spindle motor (not shown) so as to rotate at a predetermined number of revolutions. When the pickup 2 irradiates the disc 1 with laser light, recorded digital data is read out. This digital data is recorded in units of the sector shown in FIG. 7, but a sector sync, sector address, and sector header are added to the beginning of each sector. The pickup 2 reads each sector described above, and the focus control and tracking control thereof are performed by the servo circuit 9 under the control of the system control 7 by the focus error signal and the tracking error signal obtained from the demodulation circuit 3. ing.

Then, the sector demodulated by the demodulation circuit 3 is error-corrected by the ECC 4, and the writing position is controlled by the sector address where the data is detected, and is written in the buffer 5. The buffer 5 has a storage capacity capable of accumulating at least 2 GOP worth of digital data. In addition, from the buffer 5 to FIG.
Data of GOPs in the frame order shown in (b) are sequentially read, and the I picture, P picture, and B picture forming the GOP are decoded by the decoder 6, and the video signal of each frame is reproduced and output ( VIDEO OUT). In this way, when the normal play button of the operation unit key 8 is operated, output from the decoder 6 (VIDEO OUT
The reproduced image is reproduced on the display device by supplying the reproduced video signal to the display device.

The operation of the buffer 5 and the decoder 6 in this case is schematically shown in FIG. 2. In this case, the buffer 5 is 3G.
It is assumed to have a storage capacity of OP. In this figure, the sectors read from the disk 1 are written in the buffer 5, and GOP. 1, GOP. 2, GO
P. 3 GOPs are accumulated in the buffer 5 in order of 3,
Further, the GOP. 0 is supplied to the decoder 6 to indicate that decoding is in progress, and the decoded video signal (VIDEO OUT) is output.

The decoder 6 includes a GOP. When the decoding of 0 is completed, the buffer 5 receives GOP.0. GO one after zero
P. 1 is read and supplied to the decoder 6. Then, the system control 7 controls the pickup 2 to access the disc 1 and newly read GOP. 4 is stored in the buffer 5. In this way, the video signals are reproduced one after another and displayed on the display device. It should be noted that the rate of the data read from the disk 1 is set higher than the rate of the video signal output from the decoder 6, and the buffer 5
When a certain amount of data is stored in the system, the system control 7 sets the reproduction from the pickup 2 to the pause mode, and when the amount of data stored in the buffer 5 becomes small, the system control 7 sets the reproduction mode to store the data in the buffer 5.

By the way, the ratio of the compressed code amount before being decoded by the decoder 6 and the code amount after decoded is made different according to the complexity and flatness of the video signal as described above. However, since the rate of the video signal that is decoded and output is generally a constant display speed, the supply amount of the compressed coded signal that is input to the decoder 6 is
In order to make the decoded and output video signal continuous, a random rate is set according to the complexity and flatness of the video signal. As described above, the buffer 5 is provided to buffer different rates, and the rate of writing to the buffer 5 is usually higher than the rate of output from the decoder 6. It is controlled so that a new GOP is written in the buffer 5 when an empty area is generated in 5.

Next, the operation of the buffer 5 and the decoder 6 when the operation key 8 is operated to enter the still mode is schematically shown in FIG. 3. In general, when the still mode is entered, the images before and after that are frame-advanced. There is a high possibility that a reverse playback mode or the like will be made. As shown in this figure, when the stationary mode is set, the system control 7 controls the pickup 2 to access the disc 1 to thereby perform GOP. 0 and GOP. 1 from 0
The previous GOP. -1 is newly read and written in the buffer 5. As a result, when the operation key 8 is further operated to continue the still mode and then the backward frame advance button is operated, the decoder 6 is decoding
OP. G to be decoded after finishing decoding 0
OP. -1 can be immediately read from the buffer 5.

Therefore, the GO which is being decoded by the decoder 6 is
P. After the decoding of 0 is completed, GOP. -1 can be immediately supplied to the decoder 6, and from the decoder 6, a video signal (VIDEO OUT) obtained by quickly decoding GOP-1.
Is supplied to the display device, so that the user does not feel uncomfortable when the reverse playback mode is set. In addition,
GOP. 0 is also written in the buffer 5 because it has already been decoded in the backward frame advance mode.
OP. It is necessary to decode the pictures forming the GOP. This is because the I picture located at the beginning of 0 is required. Also,
If the forward frame feed is instructed after the stop mode,
GOP. 0 followed by GOP. 1 may be read from the buffer 5 and supplied to the decoder 6.

Further, the capacity of the buffer 5 is increased as shown in FIG. 4, and when the still mode is set, as shown in FIG. When 0 is being decoded, the pickup 2 is controlled to access the disk 1 and a new GOP. 0, GOP. If -1, GOP-2 are written in the buffer 5, not only frame feeding but also variable speed reproduction such as double speed can be supported. Further, not only the reverse reproduction but also the variable speed reproduction during the forward reproduction can be supported.
When the variable speed reproduction mode is set, it is possible to support variable speed reproduction such as double speed by reproducing only I pictures or only I pictures and P pictures.

[0028]

As described above, according to the present invention, the special reproduction mode such as the reverse reproduction mode is generally set after the still mode is generally selected. Therefore, the special reproduction mode is set after the still mode. Sometimes already at least 1 in time
Since the previous GOP is read and stored, the special playback screen can be displayed quickly. Further, if the buffer has a sufficiently large capacity, if a plurality of GOPs before and after the GOP including the video being output are stored in the buffer, not only backward playback but also
For forward playback, not only the frame advance but also 1/2,
It becomes possible to support slow reproduction of 1/4 or variable speed reproduction such as double speed. Thus, the present invention
By storing the past data that is a little earlier in the buffer all the time, it is possible to reduce the number of times of disk access, and it is possible to perform special reproduction only by controlling the buffer even during normal reproduction.

[Brief description of drawings]

FIG. 1 is a system diagram showing a configuration of an embodiment of a data reproducing apparatus of the present invention.

FIG. 2 is a diagram schematically showing operations of a buffer and a decoder during normal reproduction in the data reproducing apparatus of the present invention.

FIG. 3 is a diagram schematically showing operations of a buffer and a decoder in a still mode in the data reproducing device of the present invention.

FIG. 4 is a diagram schematically showing another example of the operation of the buffer and the decoder in the still mode in the data reproducing device of the present invention.

FIG. 5 is a diagram showing a configuration example of a conventional encoder that encodes a digital moving image signal.

FIG. 6 is a diagram showing a structure of inter-frame prediction in GOP and a structure of a recording frame.

FIG. 7 is a diagram showing a relationship between a sector recorded on a disc and a picture forming a GOP.

[Explanation of symbols]

 1 Disc 2 Pickup 3 Demodulation Circuit 4 ECC 5 Buffer 6 Decoder 7 System Control 8 Operation Key 9 Servo Circuit

Claims (4)

[Claims] 1. A data reproducing method for reproducing an image signal by demodulating data read by a pickup from a disc and decoding the data via a buffer, wherein the buffer is a GOP composed of a plurality of frames for at least 2 GOPs. By storing at least 1 GOP of data including a GOP temporally immediately preceding the GOP being decoded from the disk and storing it in the buffer when the still mode is instructed. A data reproducing method characterized in that it is equipped with a special reproduction mode. 2. The data reproducing method according to claim 1, wherein the special reproduction mode is a reverse reproduction mode. 3. Data comprising demodulation means for demodulating data read by a pickup from a disc, a buffer for temporarily storing the demodulated data, and a decoder for decoding the data read from the buffer into an image signal. In the playback device, the buffer has a capacity capable of storing at least 2 GOPs each composed of a plurality of frames, and when a still mode is instructed, the buffer immediately before the GOP decoded by the decoder is temporally preceding. A data reproducing apparatus characterized in that at least one GOP including a GOP is read from the disk and stored in the buffer to prepare for a special reproduction mode. 4. The data reproducing apparatus according to claim 3, wherein the special reproduction mode is a reverse reproduction mode.