GB2340288A - Digital video replay using buffer memories - Google Patents

Description

1 2340288 DIGITAL VIDEO RECORDING AND REPLA This invention relates to

digital video recording and replay.

To record and replay digital video signals, particularly in an uncompressed or lossless compressed form, requires large quantities of data to be stored and retrieved.

Traditionally video recording has been carried out using a tape medium, but now computer disk storage is becoming more common. Disk storage has the advantage of offering random access to the recorded video signals.

However, it remains difficult to handle the large quantities of data involved.

io This is particularly true where the video data is recorded on a server apparatus - for example, a high capacity disk array - but is actually required for display or processing by a client device remotely connected to the server device.

A further difficulty does not apply to most other catecories of stored data - this is the need to be able to replay video signals in reverse sequence as well as in a forward sequence, and the need to replay in a slow motion or freeze frame mode.

This invention provides digital video replay apparatus for replaying a video signal stored in a random access data storage device as a succession of video images, the apparatus comprising:

three or more buffer memory areas, each having the capacity to store data representing at least one video briage; a write controller operable:

(a) to detect available buff6r memory areas, being those of the buffer memory areas which do not contain data representing ail imaoe which will be required for replay in the current replay direction; and (b) to retrieve data from the data storage device representing a next required video frame which is not already stored in one of the memory areas, the retrieved data beina stored in an available buffer memory area; and a read controller for controlling replay of data representing a currently required video image from the memory areas, the read controller beincy operable to restrict, during reading of data representing the currently required image, ATite access to the buffer memory area or areas containing data representing the currently required ima-ge.

The invention thus provides an elegantly simple way of retrieving data from a data storage device and making, it available for video replay. Three or more memory areas are used as replay buffers. As data is retrieved from the storage device into one memory area, two more are available for a current video replay operation. Of these two, a currently required image may be stored in only one (in which case the other memory area is available to hold a next required image) or it may overlap the two.

As a memory area (or areas) is required for a reading operation, the read controller "locks" that area or those areas. This prevents write access to the area(s) currently being used for a reading operation.

to Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Figure I is a schematic diagram of a digital video recording and replay apparatus; Figure 2 schematically illustrates forward replay of video data using three buffer memorv areas; and Figure ') schematically illustrates reverse replay of video data using three buffer memory areas.

Referring now to Figure 1, digital video recording and replay apparatus comprises a central processing unit (CPU) 10, one or more user input devices 20 (e. 2.

a mouse or keyboard), a system memory 30, a display driver 40 coupled to a display memory 50 and a display screen 60. The system memory '30 (and/or the CPU 10) is coupled by an "UltraSCSI" data link to a disk array storage device 70.

Video data is stored on the disk array 70, having been received into the apparatus via a video interface 80. In this embodiment, the video data is stored as a series of frames in uncompressed form, so that each frame occupies 1.2 MB of disk space.

When video data is read from the disk array 70, it is first stored in the system memory 30, which is partitioned into three buffer memory areas. The partitioning is described below with reference to Figures 2 and 3. A larger number of buffer memory areas could of course be used instead, and a plurality of distinct memory devices could be used instead of the present partitioning arranaement.

3 The video data is read. from the partitioned system memory 30 under the control of the CPU 10, a frame at a time. It is then either output to other apparatus via the video interface 80 or passed, via the display driver 40, for display on the display screen 60.

Figure 2 schematically illustrates forward replay of video data using the three buffer memory areas in the system memory 30.

The upper part 100 of Figure 2 represents the continuous series of frames as output by the disk array. The lower part of Figure 2 represents the three buffer memory areas 110, 120, 130.

Each buffer memory area is 4 MB long, so it can accommodate 3 full frames plus part of a fourth. At the start of the process, the three buffer memory areas are filled in sequence, as shown in Figure 2.

When it is desired to read out frame 0, the 1.2 MB portion of buffer I 10 is "locked", so that writin to that area is inhibited. The data representing frame 0 is 9 t:1 read out and that portion is unlocked. The portion containing frame I is then locked, the frame read out and the portion unlocked and so on. When frame 3 is read, a portion of buffer 110 and a portion of buffer 120 must be locked for the duration of the reading process.

During the reading process so far, buffers I 10 and 120 have been partially locked at various times. Buffer 130 has been free to receive new data, albeit that it already contains the next-required data. So, in the writing operation, the CPU (controlling overall operation of the system) is operable to detect available buffer memory areas, being those of the buffers which do not contain data representing an image which has yet to be replayed in the current replay direction, and to load newly retrieved video data into such an available buffer.

Once frames 0 to 3 have been read, buffer 110 is ready to receive new data.

Assuming the read direction is still a forward one, this will be data representing frames I I to 13 and a part of frame 14. The writing and readincr process then continues cyclically.

Fiaure 3 schematically illustrates reverse replay of video data using the three buffer memory areas. In particular, Figure 3 shows the effect of a transition to re,.'erse play operation at the time that frame 3 is being read.

4 During reading of frame 3, that portion of buffers 110 and 120 containing frame 3 is locked. If at that time the current replay direction is changed to a reverse direction, the next required frame for replay will no longer be fi-ame 4 but will instead be frame 2. Also, the whole contents of buffer 1 -3)0 will now not be required.

Since a part of buffer 120 is locked, the write controller writes the next required data (namely frames -1, -2, --3) and part of 4) into buffer 130. So, reading can now progress backwards through buffer I 10, reading frames 2, 1 and 0, and from there to buffer 130 where frame -1 can be read. As soon as buffer 120 is unlocked (i.e. at the end of the reading process for frame 3), that too can be refilled with next io required data (part of frame -4, frame -5, frame -6 and part of frame - 7) as it contains data no longer required in the current reading direction.

Claims (8)

1. Digital video replay apparatus for replaying a video signal stored in a random access data storage device as a succession of video images, the apparatus comprising:

three or more buffer memory areas, each having the capacity to store data representing at least one video image; a write controller operable:

(a) to detect available buffer memory areas, being those of the buffer memory areas which do not contain data representing an image which will be required for replay in the current replay direction; and (b) to retrieve data from the data storage device representing a next required video frame which is not already stored in one of the memory areas, the retrieved data being stored in an available buffer memory area; and a read controller for controlling replay of data representing a currently required video image from the memory areas, the read controller being operable to restrict, during reading of data representing the currently required image, write access to the buffer memory area or areas containing data representing the currently required image.

2. Apparatus according to claim 1, in which the read controller is operable to inhibit, during reading of data representing the currently required image, write access I C to that part of the buffer memory areas containing data representing the currently required image.

1.1 1 Apparatus according to claim I or claim 2, comprising a random access data I storage device for storing data representing the video images and connected to supply data to the memory areas.

4. Apparatus according to any one of claims I to _3), comprising, useroperable control means for altering a video replay direction or a video replay speed of the apparatus.

6

5. Apparatus according to any one of the preceding claims, in which the replay apparatus is connected to the data storage device by an UltraSCSI data transfer connection.

6. Apparatus according to any one of the preceding claims, in which the data storage device is an array of magnetic disk devices.

7. Apparatus according to any one of the preceding claims, in which each buffer memory area is about a 4 Megabyte memory area, and data representing each image io occupies about 1.2 Megabytes.

8. Digital video replay apparatus substantially as hereinbefore described with reference to the accompanying drawings.