AT402122B - Reproducing apparatus and reproducing method for digital data - Google Patents

Abstract

Reproducing apparatus and reproducing method for digital data, with which reproduction is possible for a long time interval without impairment of the image quality. Data are reproduced from an optical disc by a pick-up device and are transferred to a ring buffer memory, where they are stored. Data read out from the ring buffer memory are transferred to a video code buffer of a coding part, where they are stored. The data stored in the video buffer are coded in the coding part and represented on a display. A track-jump assessment stage generates a track jump command to make the pick-up device jump back to an earlier track when the volume of data stored in the ring buffer memory reaches a predetermined value. <IMAGE>

Description

AT 402 122 B

The invention relates to a playback device for digital data according to the preamble of claim 1.

When moving images are digitally recorded and reproduced, a method of compressing data is used because a very large amount of data is affected. Fig. 1 shows the structure of an exemplary device that records and reproduces a moving image in compressed form.

1, reference is now made. A video signal that is output from a video camera 1 is converted by an analog / digital (A / D) converter 2 from an analog signal into a digital signal and then stored in a frame memory 3. The data stored in the frame memory 3 are then read out of the frame memory 3 and input into a DCT (discrete cosine transformation) stage 5. The DCT stage 5 carries out DCT processing of the input data. Data output from the DCT stage 5 are input to a quantization stage 6 and quantized, whereupon they arrive at a VLC (variable length coding) stage 7, where they are converted into variable length codes, for example in Huffman codes. The variable length codes of VLC stage 7 are applied to a video code buffer 8 and stored therein.

The data quantized by the quantization stage 6, if they are data of an I-picture (intraco-dated picture) or a P-picture (forward predictable coded picture), are applied to an inverse quantization stage 10 and inversely quantized. The data inversely quantized by the inverse quantization stage 10 are applied to an IDCT (inverse discrete cosine transformation) stage 11, where they undergo IDCT processing. Output data of the IDCT stage 11 are via an addition stage 12 at a frame memory 13 in which they are stored. In the meantime, a motion sensing stage 14 senses motion of a frame stored in the frame memory 3, delivering a motion vector to the VLC stage 7 and a motion compensation stage 15. The motion compensation stage 15 compensates for motion of the data stored in the frame memory 13 in accordance with the motion vector, and applies the data thus compensated to a subtraction stage 4 and the addition stage 12. The subtraction stage 4 subtracts the data input from the motion compensation stage 15 from the data input from the frame memory 3. This creates a P-picture that uses an I-picture or a P-picture that is arranged at the front in time and is already decoded, or a B-picture (in two-way predictively encoded picture) that uses three pictures as predictive pictures, one I-picture or one P-picture that is arranged at the front in time and already decoded, another I-picture or another P-picture that is behind in time arranged and already decoded, and have an interpolation image that is generated from the two images. An I-picture is generated when only data that are output from the frame memory 3 are at the DCT stage 5, without using data from the motion compensation stage 15.

The addition stage 12 adds the motion-compensated data coming from the motion compensation stage 15 and the data supplied from the IDCT stage 11 by a decoded picture of an I-picture. of a P-picture or a B-picture, and puts the picture thus generated to the frame memory 13 so that it is stored in the frame memory 13. This means that image data obtained by decoding the same data as quantized by the quantization stage 6 and applied to the video code buffer 8 via the VLC stage 7 are stored in the frame memory 13. With this, data of a P picture or a B picture can be obtained using the data stored in the frame memory 13. In the meantime, a speed controller 9 monitors an amount of data stored in the video code buffer 8, and adjusts the quantization step size of the quantization stage 6 so that the stored amount does not overflow or leak. The bit speed Rv with which data is applied from the VLC stage 7 to the video code buffer 8 is thus changed in such a way that the video code buffer 8 is prevented from overflowing or running out.

Then, the data thus stored in the video code buffer 8 is transferred to an optical disc 16 at a fixed transfer rate and written thereon. The coding part of the recording and reproducing device is constructed as described so far.

The structure and operation of the decoding part of the recording and reproducing apparatus will now be described. In the decoding section, data reproduced from the optical disc 16 is transferred to a video code buffer 21 at a fixed transfer rate and stored there. Data read from the video code buffer 21 is applied to an IVLC (inverse length variable coding) stage 22, where it undergoes IVLC processing. After this IVLC processing of the input data is completed, the IVLC stage 22 supplies data for an inverse quantization stage 23. Thereupon, the IVLC stage 22 makes a code request to the video code buffer 21 in order to 2

AT 402 122 B to request the transmission of new data.

When such a code request is received, the video code buffer 21 transmits new data to the IVLC stage 22. The transmission speed Rv is then set to a value equal to the bit speed at which data is transmitted from the VLC stage 7 to the video code buffer 8 in the coding section, so that the video code buffer 21 cannot overflow or leak when data is transferred from the optical disc 16 to the video code buffer 21 at a fixed transfer rate. In other words, the bit speed in the coding part is set so that the video code buffer 21 does not overflow or leak in the decoding part.

The inverse quantization stage 23 inversely quantizes the data applied from the IVLC stage 22 in accordance with data of the quantization step size provided by the IVLC stage 22. The quantization step size and a motion vector which the IVLC stage 22 applies to a motion compensation stage 26 are supplied by the speed controller 9 and the motion sensing stage 14 for the VLC stage 7 and are stored on the optical disc 16 by means of the video code buffer 8 together with the image data in Coding part recorded and then reproduced from the optical disc 16.

An IDCT stage 24 carries out IDCT processing of the data which are present from the inverse quantization stage 23. If the IDCT-processed data is I-image data, it is, as it is, applied to a frame memory 27 via an addition stage 25 and stored therein. On the other hand, if the data output from the IDCT stage 24 is P-image data for which an I-image is a prediction image, I-image data are read out from the frame memory 27 and subjected to motion compensation by the motion compensation stage 26, and then sent to the addition stage 25 be placed. The addition stage 25 adds the data output by the IDCT stage 24 and the data output by the motion compensation stage 26 to generate P-image data. The data generated in this way are also stored in the frame memory 27.

Otherwise, if the data output by the IDCT stage 24 is B-image data, I-image data or P-image data is read out from the frame memory 27 and then subjected to motion compensation by the motion compensation stage 26, whereupon it is applied to the addition stage 25 will. The addition stage 25 adds the data output by the IDCT stage 24 as well as the data received by the motion compensation stage 26, so that decoded B-picture data are obtained. This data is also stored in the frame memory 27.

The data stored in the frame memory 27 in this way are converted from digital values into analog values by a digital / analog (D / A) converter 28 and then applied to a display 29 and displayed there.

In this way, redundancy in one frame is reduced by DCT processing, and redundancy between frames is reduced by using a motion vector, and a high compression ratio is achieved by a combination of the methods.

In the conventional recording and reproducing apparatus, data is thus transferred from the optical disc 16 to the video code buffer 21 at a fixed speed. In this case, the quantization step size of the quantization stage 6 is previously controlled in accordance with a stored amount of data in the video code buffer 8 of the coding section to adjust the transmission speed from the VLC stage 7 to the video code buffer 8 so that the video code buffer 21 does not overflow or leak. For example, while an I-picture is used in an MPEG in a time interval of about 0.5 seconds, the amount of data of a P-picture or a B-picture is much smaller than the amount of data of an I-picture. This periodically changes the amount of data that must be transferred to IVLC stage 22 in a time interval of 0.5 seconds. However, since the video code buffer 21 is provided, when the change in the amount of data per unit time is within the capacity range of the video code buffer 21, it becomes possible to track the change in the amount of data, whereby the data is regularly applied to the IVLC stage 22.

However, if, for example, a large number of complicated screens have to be coded one after the other, the quantization step size of the quantization stage 6 must be set to a high value since the bit speed during the transmission from the VLC stage 7 is higher in order to prevent the video code buffer 8 from overflowing, this leads to the problem that the image quality changes.

A promising solution, for example, seems to be to set the quantization step size of the quantization stage 6 so that a code sequence output from the VLC stage 7 at a variable speed as it is is recorded on the optical disc 16 to provide a uniform image quality to reach. However, when such an optical disc 16 is reproduced in a conventional reproducing apparatus, the video code buffer 21 will leak when the decoding of FIG

AT 402 122 B complicated screen images takes several seconds. On the other hand, if decoding of simple screens continues, the video code buffer 21 is overflowed. Basically, you cannot get properly rendered frames.

Furthermore, there is another solution in which the average bit speed is previously set to such a high value that the device can handle complicated screen images, for example. With this solution, however, even with a simple screen image, a lot of data is transmitted, thereby shortening the time in which an optical disc can be recorded or reproduced.

Furthermore, in a conventional device, error correction is carried out for the data read out from the optical disc 16 by an error correction stage (not shown). However, if a reproduced signal is deteriorated, for example, by dust stuck on the optical disk 16, or if the tracking control is disabled by external mechanical vibrations, the error correction becomes impossible, thereby degrading the image quality.

The aim of the invention is to propose a playback device of the type mentioned at the beginning with which a picture can be reproduced from a disk with a constant picture quality, even if the picture was recorded on the disk in a code sequence with variable speed.

According to the invention, this is achieved in a playback device of the type mentioned at the outset by the characterizing features of claim 1.

A very largely error-free reproduction can be achieved by the proposed measures. For example, the data tapped from an optical plate and e.g. be written into a ring buffer memory, at least storing the data from one track. These can be fed to a decoding stage and decoded in this. The tapping device can be controlled via the step control stage as a function of the amount of data stored in the ring buffer memory.

Another object of the invention is to provide a reproduction method according to the preamble of claim 12, with which images of a disk with limited capacity can be reproduced for a long period of time.

This is achieved on the basis of a reproduction method according to the preamble of claim 12 by the characterizing features of claim 12.

The above and other objects, features and advantages of this invention will become apparent from the following description of a preferred embodiment and in conjunction with the accompanying drawings, in which like reference numerals are used to refer to the same or similar parts in different views, and in which shows:

1 shows the block diagram of an exemplary conventional data recording / reproducing device:

Fig. 2 is a diagram showing a change in the amount of data reproduced from an optical disc with the data recording / reproducing apparatus of Fig. 1;

Figure 3 is a block diagram of a data player of a preferred embodiment of this invention;

Fig. 4 is a diagram showing the track jump in the data reproducing apparatus of Fig. 3;

Fig. 5 is a diagram showing the construction of a sector of an optical disk used in the data reproducing apparatus of Fig. 3;

Fig. 6 is a diagram showing an amount of data to be written in a ring buffer memory of the data reproducing apparatus of Fig. 3;

Fig. 7 is a diagram showing an amount of data to be written in the ring buffer memory of the data reproducing apparatus of Fig. 3 in the case of a track jump;

8 (a) and 8 (b) are diagrams showing modes for writing and reading data to and from the ring buffer memory of the data reproducing apparatus of Fig. 3;

9 (a) and 9 (b) of FIGS. 8 (a) and 8 (b) are similar views, but in which different modes of operation for writing and reading data into or from the ring buffer memory of the data reproducing device of FIG. 3 are shown;

10 (a) and 10 (b) are similar views, but in which different operating modes for writing and reading data into and out of the ring buffer memory of the data reproducing device of FIG. 3 are shown;

Fig. 11 is a diagram showing a change in the amount of data reproduced from an optical disc with the data reproducing apparatus of Fig. 3;

FIG. 12 shows a diagram in which the writing in and reading out of data into or from the ring buffer memory of the data reproducing device from FIG. 3 is shown when an error is restored; FIG. FIG. 13 is a view similar to FIG. 12, but showing conditions that limit the recovery of an error in the data reproducing device of FIG. 3; and 4th

AT 402 122 B

14 (a) and 14 (b) are diagrams in which different operating modes for writing and reading data into or from the ring buffer memory of the data reproducing device of FIG. 3 are shown when an error is restored.

First, reference is made to Fig. 3 which shows the block diagram of a data playback device according to a preferred embodiment of this invention. It should be noted that similar components are designated with the same reference numerals as in Fig. 1. Data recorded on an optical disc 16 is reproduced by a tapping device 41. The tapping device 41 directs a laser beam onto the optical disc 16, and reproduces data recorded on the optical disc 16 from the reflected light of the optical disc 16. A demodulation stage 42 demodulates the reproduction signal which is output by the tapping device 41, and applies the demodulated reproduction signal to a sector sampling stage 43. The sector scan stage 43 samples an address recorded for each sector of the optical disk 16 from that applied by the demodulation stage 42, and applies the sampled address to a control stage 46. The sector scan stage 43 further provides data in a sector synchronized relationship for an ECC stage 44 in a subsequent step. Furthermore, if the sector scan stage 43 does not scan an address or determines that the scanned addresses are not consecutive numbers, it indicates a sector number irregularity signal a track jump judging level 47.

The ECC stage 44 samples an error in data applied from the sector sample stage 43, corrects the error using a redundant bit that is added to the data, and applies the corrected data to a track jump ring buffer 45, which is is a first-in / first-out (FIFO) memory. Furthermore, if the ECC stage 44 cannot correct the data error, it outputs an error occurrence signal to the track jump judging stage 47. The control stage 46 controls the writing into and the reading out of the ring buffer memory 45, monitoring a code request signal which is output by an IVLC stage 22 via a video code buffer 21 and requests data.

The track jump judging stage 47 monitors an output of the control stage 46 and then, when a track jump is required, supplies a track jump signal for a tracking control stage 48, so that the playback point of the tapping device 41 jumps by one track. Further, the track jump judging section 47 samples a sector number irregularity signal from the sector scanning section 43 or an error occurrence signal from the ECC section 44, and outputs a track jumping signal to the tracking control section 48 so that the reproducing point of the pickup 41 jumps one track.

An output of the ring buffer memory 45 is applied to a video code buffer 21 of a decoding part 31. The structure of the decoder part 31 including the video code buffer 21 to form a display 29 is the same as in the device shown in FIG. 1. However, in the present embodiment, the frame memory 27 has a pair of frame memories 27a and 27c, each of which can store an I-picture or P-picture, and another frame memory 27b to store a B-picture 2u therein.

The operation of the data reproducing apparatus of this embodiment will now be described. The tapping device 41 directs a laser beam onto the optical disk 16 and reproduces data recorded on the optical disk 16 from the light reflected by the optical disk 16. The reproduction signal emitted by the tapping device 41 is applied to the demodulation stage 42 and demodulated. The data demodulated by the demodulation stage 42 are applied via the sector sampling stage 43 to the ECC stage 44, in which a data error is sampled and corrected. It should be noted that if a sector number (address assigned to a sector of the optical disk 16) is not properly scanned by the sector scanning section 43, a sector number irregularity signal is output to the track jump judging section 47. The ECC stage 44, when data is found whose error correction is impossible, outputs an error occurrence signal to the track jump judging stage 47. Data on which data correction has been carried out are applied to the ring buffer memory 45 by the ECC stage 44 and stored therein.

The control stage 46 reads an address of each sector from an output of the sector scanning stage 43 and specifies a write-in address (write-in location (WP)) of the ring buffer memory 45 which corresponds to the read address. Furthermore, the control stage 46 determines, depending on a code request signal from the video code buffer 21, a readout address (playback location (RP)) of data written in the ring buffer memory 45, reads data from the playback location (RP) thus determined and reads out applies the data to the video code buffer 21 to store the data in the video code buffer 21.

The data read out from the video code buffer 21 are applied to the IVLC stage 22 at a transmission speed Rv. The IVLC stage 22 carries out IVLC processing of the received data, and after the end of the IVLC processing of the received data it converts it to inverse 5

AT 402 122 B

Quantization level 23 delivers. Furthermore, the IVLC stage 22 outputs a code request signal to the video code buffer 21 in order to request the delivery of new video data. The inverse quantization stage 23 carries out an inverse quantization of the received data and delivers the inverse quantized data to the IDCT stage 24. The IDCT stage 24 carries out IDCT processing of the received data and applies this to the addition stage 25.

If the data output from the addition stage 25 corresponds to an I picture, it is stored in the frame memory 27a or 27c. On the other hand, if the data output from the addition stage 25 corresponds to a B picture, it is stored in the frame memory 27b. However, if the data corresponds to a P picture, it is stored in the frame memory 27a or 27c. Data of an I-picture and a P-picture stored in the frame memories 27a and 27c are, if necessary, applied to the addition section 25 through the motion compensation section 26 so as to be used for decoding a subsequent P or B picture be used. Data stored in one of the frame memories 27a to 27c is selected with a switch 27d, the selected data being D / A converted by the D / A converter 28 and then applied to the display 29 and then displayed.

The optical disc 16, which is rotated at a predetermined speed, is divided into a plurality of sectors. Each sector is formed, for example, by an initial part and a data part, as shown in FIG. 5, wherein, for example, clock recesses in order to generate clocks, wobbled recesses for the wake, etc. are formed as recesses in the initial region. Video data etc. are stored in the data area. As a result, the data transfer speed to the ring buffer memory 45 changes periodically for each sector, as shown in FIG. 6. In particular, no data transmission takes place in the initial part, only data from the data part being transmitted to the ring buffer memory 45 and being stored there. An average data transmission speed to the ring buffer memory 45 is denoted by Rm in FIG. 6.

Let us now return to Fig. 3. The control stage 46 reads out data stored in the ring buffer memory 45 and applies it to the video code buffer 21 in response to a code request signal for the video code buffer 21. However, if, for example, data is continuously processed from simple screens, so that the data transfer speed from the video code buffer 21 to IVLC level 22 per unit time becomes low, the data transfer rate from the ring buffer memory 45 to the video code buffer 21 is also reduced. There is thus the possibility that the amount of data stored in the ring buffer memory 45 can increase until the ring buffer memory 45 overflows. In order to prevent this, the track jump judging stage 47 calculates (samples) an amount of data currently stored in the ring buffer memory 45 from the writing point (WP) and the reproducing point (RP). When the amount of data exceeds a predetermined reference value which has been set in advance, the track jump judging section 47 judges that there is a possibility that the ring buffer memory 45 may overflow by issuing a track jump command to the tracking control section 48.

Further, when the track jump judging section 47 samples a sector number deviation signal from the sector sensing section 43 or an error occurrence signal from the ECC section 44, it calculates an amount of data remaining in the ring buffer memory 45 from the write-in address (WP) and the read-out address (RP), and further calculates an amount of data necessary to ensure readout from the ring buffer memory 45 to the video code buffer 21 while the optical disk 16 is making one turn from a current track location (while waiting for one turn of the optical disk 16). If the remaining amount of data in the ring buffer memory 45 is large, the ring buffer memory 45 will not leak even if data is read from the ring buffer memory 45 at the highest possible transmission speed. Accordingly, the track jump judging section 47 judges that the recovery of an error is possible by reproducing the optical disk 16 at the error occurrence point again by the pickup 41, and issues a track jump command to the tracking control section 48.

When the track jump command is issued from the track jump judging section 47, the tracking control section 48 jumps from the reproducing point of the pickup 41, for example, from one point A to another point B on the inside by one track pitch, as shown in FIG. For a time interval when the reproducing point advances from point B to point A due to one revolution of the optical disk 16, i.e. for a time interval until the sector number originating from the sector scanning stage 43 is equal to the original sector number from which the track jump was carried out, the control stage 46 then prevents new data from being written into the ring buffer memory 45. If necessary, the data is already stored in the ring buffer memory 45 stored data transferred to the video code buffer 21. 6

AT 402 122 B

Even if a sector number obtained from the sector scanning stage 43 after the track jump matches the sector number obtained when the track jump when the amount of data stored in the ring buffer memory 45 exceeds the predetermined reference value, i.e. then, if the ring buffer 45 is likely to overflow, data writing to the ring buffer 45 will not continue, and a track jump will be performed again. A method by which data is transferred to the ring buffer memory 45 when a track jump back by one track pitch is performed is shown in FIG. 7.

From Fig. 7, it can be seen that for a period of time until the optical disk 16 has made one full revolution after the track jump by one track pitch, until the reproduction point returns to the original reproduction point, the writing of new data into the ring buffer memory 45 is not carried out . The data transfer to the ring buffer memory 45 thus takes place after an additional time has expired which is equal to the time interval of such a track jump. The average transmission speed to the ring buffer memory 45 thus changes by values that are less than Rm. In other words: Rm is a permissible maximum average transmission speed.

Here, the ring buffer memory 45 has a capacity sufficient to store therein data from at least one track (one revolution) of the optical disk 16, i.e. at least one storage capacity corresponding to a maximum round trip interval of the optical disk multiplied by Rm. For example, when the optical disk 16 is a CLV disk, the round trip interval at the outermost periphery of the optical disk 16 is a maximum, whereby the ring buffer memory 45 has at least a storage capacity of one track (one revolution) at the outermost periphery of the optical disk 16 owns. In short, the storage capacity is at least equal to the round trip interval at the outermost periphery of the optical disk 16 multiplied by Rm.

If the maximum transmission speed from the ring buffer memory 45 to the video code buffer 21 is designated Rc, Rc is set to a value equal to or slightly less than Rm (Rc $$ le $$ Rm). When Rc is set to this value, a code request for data transfer from the video code buffer 21 to the ring buffer memory 45 can be freely carried out regardless of a timing of a track jump.

If Rc is substantially smaller than Rm, for example if Rc is equal to half of Rm or similar, the amount of data written into the ring buffer 45 is larger than the amount of data read from the ring buffer 45. The state in which the ring buffer memory 45 is almost filled with data thus remains. On the other hand, when the optical disc 16 is a CLV disc, the amount of data reproduced when the optical disc 16 makes one full revolution differs significantly depending on whether the data is of an inner circumference or an outer periphery of the optical disc 16. When the storage capacity of the ring buffer memory 45 is set for an outermost periphery of the optical disk 16 where the amount of data in the optical disk 16 is a maximum, there is enough space in the storage capacity of the ring buffer memory 45 on an inner periphery of the optical disk 16. There is therefore a high probability that a fault recovery can be made by a return, as described above. If the storage capacity of the ring buffer memory 45 is further increased, the likelihood of error recovery is greatly increased. If the storage capacity on the outermost circumferential track of the optical disk 16 is more than twice as large, the error recovery can always be performed regardless of a residual data in the ring buffer 45.

The relationship between the capacity of the ring buffer memory 45 and the transmission speed will now be described. 8 (a) and 8 (b) show the modes of writing and reading data into and out of the ring buffer memory 45 when data is read out from the ring buffer memory 45 at a fixed high bit speed. FIG. 8 (a) shows an operating mode in which the tapping device 41 reads from an outer circumference of the optical disk 16, while FIG. 8 (b) shows an operating mode in which the tapping device 41 reads from an inner circumference of the optical disk 16.

In the case of Fig. 8 (a), data is started to be written into the ring buffer 45 at a medium transfer rate Rm (location A), and the ring buffer 45 is soon filled with data, and the writing is stopped (location B). Thereupon, the tapping device 41 makes a track jump by one track distance in order to return to another track. In the meantime, the reading out of data from the ring buffer memory 45 is started (position C). After a period of time has elapsed in which the optical disk 16 makes one full revolution, data writing is started again (point D) if there is a free area in the ring buffer memory 45. This registration ends again (point E) when the ring buffer memory 45 is fully 7

AT 402 122 B. After a period of time has passed in which the optical disk 16 makes one full rotation, data writing continues (point F). In this case, the amount of data (the hatched area in Fig. 8 (a)) remaining in the ring buffer 45 decreases as the speed of reading data from the ring buffer 45 increases (since the transfer speed Rc increases). It should be noted that the dashed curve in Fig. 8 (a) indicates a place where the ring buffer memory 45 becomes full.

In the case of FIG. 8 (b), in which an operating mode for reading out from an inner circumference of the optical disk 16 is shown, no area is free in the ring buffer memory 45 even after a track jump (point B ′) has been carried out, since the time, in which the optical disk 16 makes a full revolution is shorter than that time when the tapping device 41 reads from an outer periphery of the optical disk 16. Therefore, the tapping device 41 again performs a track jump (between the points B ’and D). As a result, the amount of data remaining in the ring buffer memory 45 at point F is larger than in FIG. 8 (a), in which an operating mode for reading out from an outer circumference of the optical disk 16 is shown.

9 (a) and 9 (b) show an operation mode for writing and reading data into and from the ring buffer memory 45 when data is read out from the ring buffer memory 45 at a fixed low bit speed. Specifically, Fig. 9 (a) shows an operation mode in which the pickup 41 is located on an outer periphery of the optical disk 16 on which data is recorded at a fixed linear speed, while Fig. 9 (b) shows an operation mode in which the tapping device 41 is located on an inner circumference of the optical plate 16. The amount of data remaining in the ring buffer memory 45 after a track jump is larger than when the reading out of data is carried out at a high speed (FIGS. 8 (a) and 8 (b)).

10 (a) and 10 (b) show modes for writing and reading data to and from the ring buffer memory 45 when data is read from the ring buffer memory 45 at a variable speed that does not exceed Rc. Specifically, Fig. 10 (a) shows an operation mode in which the pickup 41 is located on an outer periphery of the optical disc 16 on which data is recorded at a fixed linear speed, while Fig. 10 (b) shows an operation mode in which the tapping device 41 is located on an inner circumference of the optical plate 16. 10 (a) and 10- (b), the reading out of data from the video code buffer 21 is shown in broken lines. A curve which indicates the reading out of data from the ring buffer memory 45 also represents the writing of data into the video code buffer 21.

Since data is usually read out from the ring buffer 45 at a variable speed, a curve indicating such a reading does not become a straight line as shown in Figs. 8 (a) to 9 (b), but becomes a polyline as shown in Fig. 10 (a) or 10 (b). 10 (a) and 10 (b), the curves showing the reading of data from the ring buffer memory 45 are the same. This is because the ring buffer memory 45 picks up a difference between the times when the optical disk 16 makes one full revolution when reading out on an inner periphery and an outer periphery of the optical disk 16. On the other hand, although the increase in the readout curve for data from the ring buffer memory 45 cannot exceed the maximum average transmission speed Rm, the transmission speed Rv of the IVLC stage 22 (the increase in the readout curve (shown in broken lines in FIGS. 10 (a) and 10 (b)) of data from the video code buffer 21) can be set to a transmission rate which is higher than the maximum average transmission rate Rm, since the video code buffer 21 is present between the ring buffer memory 45 and the IVLC stage 22.

11 shows an example in which the amount of data reproduced may change when the optical disc 16 is reproduced from start to finish. From Fig. 11, it can be seen that the amount of data reproduced per unit time is relatively large in one area of complicated frames, while the amount of data reproduced in another area of simple frames is small.

When data is thus reproduced from the optical disc 16, the transfer speed of data to the ring buffer 45 becomes fixed. However, since the track jump occurs if necessary, the average transmission speed is variable when you consider the entire interval from the start point to the end point.

12 and 13 show recovery operations with the ring buffer 45 when an error occurs when reading data from the optical disk 16. Fig. 12 shows the recovery process when data is read out from the ring buffer 45 at a variable speed. If, for example, an error occurs when reading data from the optical disk 16, for example due to mechanical vibrations, in order to render writing data into the ring buffer memory 45 unusable (point G), the tapping device 41 executes a track jump in order to read it again 8

Claims (23)

AT 402 122 B to execute data (point H) when the amount of data stored in the ring buffer memory 45 (hatched area in FIG. 12) is greater than a amount of data corresponding to one revolution of the optical disk 16. A restoration is thus achieved without influencing the reading out of the ring buffer memory 45. On the other hand, in the case of Fig. 13, if an error occurs when reading out data from the optical disc 16, for example due to mechanical vibrations, to make writing data into the ring buffer memory 45 unusable (point G), the ring buffer memory 45 becomes empty (Point H ') before reading out again because the amount of data stored in the ring buffer 45 (hatched area in Fig. 13) is smaller than an amount of data corresponding to one revolution of the optical disk 16, whereby no recovery can be performed without to influence the reading of data from the ring buffer memory 45. Then, for example, when the location where data recorded on the optical disk 16 is reproduced is an inner circumferential track, and thus the waiting time for a complete revolution of the optical disk 16 is comparatively short, so that there is sufficient space is present in the remaining storage capacity of the ring buffer memory 45, or if the storage capacity of the ring buffer memory 45 was previously set to a sufficiently large value, the recovery capacity of the ring buffer memory 45 is large if an error occurs when reading data from the optical disk 16. If data is read out from an inner periphery of the optical disk 16, even if the amount of data stored in the ring buffer memory 45 is small, error recovery can be performed (Fig. 14 (a)) because the time required for one full revolution is short. If an error occurs during the readout, a repeated readout takes place as long as the residual data value of the ring buffer memory 45 permits this (FIG. 14 (b)). If the capacity of the ring buffer 45 has previously been set to a sufficiently high value, the error recovery capability is great at all since data can be stored in the ring buffer 45. It should be noted that the optical disc 16 can be replaced by any other disc, e.g. an optomagnetic disk or a magnetic disk. While a particular embodiment of the invention has been described and disclosed, it will be appreciated that many changes and variations can be made by those skilled in the art without departing from the scope and spirit of the invention. 1. Playback device for digital data, for playing digital data in coded form from a disk, which has a tapping device, for tapping the digital data from the disk, and a decoding stage for decoding the digital data, characterized in that a first storage stage (45) for storing the digital data and for reading out the stored digital data therefrom at a first variable speed and a second storage stage (21) for storing the digital data read out from the first storage stage (45) and for feeding the digital data to the decoding stage (31) is provided, the second storage stage for storing the digital data at the first variable speed and for reading out the data stored therein, and a jump control stage being provided in order to cause the tapping device (41) in accordance with one in the first Storage level (45) saved data close to make a track jump. 2. Playback device for digital data according to claim 1, characterized in that the tapping device (41) is in operation to tap digital data which contain video data. 3. Digital data reproducing apparatus according to claim 1, characterized in that the tapping device (41) is in operation to tap the digital data from an optical disc (16) using a laser beam. 4. Playback device for digital data according to claim 1, characterized in that the device further comprises a sector scanning stage (43) for scanning a sector number from the digital data which were tapped from the tapping device (41) and a device for writing a Address for the digital data in the first storage stage (45) in accordance with the scanned sector number. 9 AT 402 122 B 5. Digital data reproducing apparatus according to claim 1, characterized in that the step control stage (46, 47) is in operation in order to make the tapping device (41) jump to a track from a current read-out point towards an inner periphery of the plate (16) to cause a track and that the first storage stage (45) has a storage capacity which is at least sufficient to store a predetermined part of the digital data corresponding to the amount of data contained in the track closest to the outermost circumference of the disk. 6. Playback device for digital data according to claim 1, characterized in that the first storage stage contains a ring buffer memory (45). 7. Digital data playback device according to claim 1, characterized in that the decoding stage (31) has a stage (22) for inverse coding with variable length (IVLC stage) in order to process an inverse for a predetermined part of the digital data Execute coding with variable length. 8. A digital data playback device according to claim 1, characterized in that the decoding stage (31) has an inverse quantization stage (23) in order to inverse quantize a predetermined part of the digital data. 9. Digital data reproducing apparatus according to claim 1, characterized in that the decoding stage (31) has a stage (24) for an inverse discrete cosine transformation (IDCI stage) to process an inverse discrete cosine transformation for a predetermined part of the digital data to execute. 10. A digital data reproducing apparatus according to claim 1, characterized in that the decoding stage (31) has a motion compensation stage (26) to perform motion compensation of the digital data in accordance with motion vector information contained in a predetermined part of the digital data. 11. A digital data reproducing apparatus according to claim 1, characterized in that the first storage stage (45) operates to receive the digital data for storage therein at a maximum average transmission speed which is greater than a maximum transmission speed from the first storage stage (45) to the second storage stage (21). 12. Reproduction method for digital data to reproduce digital data recorded on a disk, in which the data stored on the disk are tapped and written into a memory at a predetermined speed and these data are later read out, characterized in that The method further comprises the following steps: writing the tapped digital data into a first memory with a transmission speed lying within a first predetermined range: reading out the digital data stored in the first memory with a transmission speed. which is lower than the first predetermined range and variable; Storing the data read from the first memory in a second memory at a second transfer rate; and reading out the digital data stored in the second memory. 13. Reproduction method for digital data according to claim 12, characterized in that the writing of the digital data in the first memory is temporarily stopped depending on its storage capacity. 14. A digital data reproduction method according to claim 1, characterized in that the method further comprises the steps of: sampling an error in the digital data which is picked up from the disk; Generating an error occurrence signal in accordance with the sampling of such an error; and temporarily postponing the writing of the digital data into the first memory in accordance with the error occurrence signal. 10 AT 402 122 B 15. Reproduction method for digital data according to claim 12, characterized in that the digital data read out from the second memory are provided with an inverse coding of variable length, 16. Reproduction method for digital data according to claim 12, characterized in that the digital data read from the second memory are inversely quantized. 17. A reproduction method for digital data according to claim 12, characterized in that the digital data read out from the second memory are subjected to an inverse discrete cosine transformation. 18. Reproduction method for digital data according to claim 12, characterized in that motion compensation is carried out on the digital data read from the second memory. 19. A digital data reproduction method according to claim 13 or 14, characterized in that the step of tapping the digital data from the disk is carried out using a tapper, and that the step of postponing the writing of digital data is a jump of the tapper includes. 20. A digital data reproduction method according to claim 14, characterized in that the step of scanning an error includes scanning a sector number from the digital data. 21. A reproduction method for digital data according to claim 12, characterized in that the step for sampling an error comprises steps for sampling an error in the digital data and correcting the sampled error. 22. A digital data playback device according to claim 7, characterized in that the second memory stage (21) is provided for reading out at a second variable speed the digital data contained therein, the second speed being at least one above the maximum value of the first variable speed has lying value and the second storage stage (21) is connected to the stage (22) for inverse coding with variable length and supplies it with the read digital data. 23. Reproduction method for digital data according to claim 12, characterized in that the reading out of the digital data stored in the second storage stage takes place at a second variable speed within a second predetermined range, which has at least one above the maximum speed of the first predetermined range. Including 12 sheets of drawings 11