WO2005065031A2

WO2005065031A2 - Dvr and method for extending recording time

Info

Publication number: WO2005065031A2
Application number: PCT/IL2005/000015
Authority: WO
Inventors: Uri Bendelac
Original assignee: Video Codes Inc.
Priority date: 2004-01-08
Filing date: 2005-01-04
Publication date: 2005-07-21
Also published as: WO2005065031A3

Abstract

A method for extending a recording time of a tape-less digital video recorder, the method includes the stages of: trans-rating, at a tape-less digital video recorder (530), a received video stream to provide a trans-rated video stream (517); and providing the trans-rated video stream (518). A computer readable medium having code embodied therein for causing an electronic device to perform the stages of: trans-rating, at a tape-less digital video recorder (530), a received video stream to provide a trans-rated video stream (517); and providing the trans-rated video stream (518). A tape-less digital video recorder including: a random access memory unit adapted to store trans-rated video streams (520), a processor adapted to trans-rate a received video stream being stored in the random access memory unit (517); whereas a trans-rated video stream replaces a previously stored video stream (508).

Description

DIGITAL VIDEO RECORDER AND A METHOD FOR EXTENDING THE RECORDING TIME OF A TAPE-LESS DIGITAL VIDEO RECORDER

RELATED APPLICATION This application claims the priority of U.S. provisional patent titled "Method for further compressing digital video", serial number 60/535670, filed January 8 2004.

FIELD OF THE INVENTION The present invention relates to digital video recorders and methods, and more specifically, to methods for extending the recording time of a tape-less digital video recorder.

BACKGROUND OF THE INVENTION Digital video must be extensively compressed prior to transmission and storage, as each picture includes multiple pixels, and each pixel has three color- difference multi-bit values. Standard compression schemes (such as the MPEG compression standards, JPEG, H.263 and others) utilize multiple compression techniques to achieve a very significant compression ratio. Standard compression schemes, such as MPEG, includes the following steps: (i) color space conversion - converting a matrix of RGB pixel values to a matrix of luminance and chrominance values (YUV) ; (ii) Spatial transform of applying a Discrete Cosine Transform (DCT) upon the YUV matrix to provide a matrix of frequency coefficients, each frequency coefficient describes how much of a given spatial frequency is present; (iii) quantization, during which each spatial coefficient is divided by a quantizing factor such that small spatial coefficients are truncated to zero; (iv) zig-zag scanning and run-length coding the quantized matrix, for achieving a compressed representation of the quantized matrix, as a typical quantized matrix includes many zero-value coefficients; and (v) variable length coding, such as Huffman coding, to provide a compressed matrix.

In addition, compression rates are improved by addressing a sequence of video frames and taking advantage of the temporal redundancy. Accordingly, compressed video includes target video elements (such as 8X8 blocks, slices, or frames) that may be predicted by a reference video element and additional information representative of the difference between the reference video element and the target video element. This prediction is also termed motion compensation. For example, MPEG-2 standard defines three types of frames, I-frames, B-frames and P-frames. I-frames are independent in the sense that they include the entire information that is required for displaying a picture. A P-frame is decoded in response to information embedded within a previous frame, while a B-frames is decoded in response to information embedded within both a preceding and succeeding frame. The prediction is done in the picture domain on an 8x8 block basis. Each 8x8 target block is compared to the content of the reference frame (the previous frame in the case of the P-frame) to find the best matching group of 8x8 reference elements (e.g.- the reference block) . The offset between each 8x8 target block and the reference block is embedded within a motion vector. It is noted that the reference block may not be aligned with the 8x8 blocks of the reference frame, and may intersect with up to four blocks (e.g. - 5 reference blocks) . Video data recorders are well-known in the art. Initially, video data recorders were designed to record video signals on video tape and to allow play back of recorded video signals from the tape. Of course, video 1.0 tapes require sequential recording and playback limiting the functionality of such machines. U.S. patent 5493456 of Augenbraun et al. titled "Method and apparatus for increasing the recording time of a digital video tape recorder", which is incorporated

15 herein by reference, describes a method for increasing the recording time of a digital video tape recorder ("VTR") that stores video streams on tape. The method includes adjusting a rotation rate of a headwheel that is surrounded by multiple recording heads to the bit

20 rate of a compressed video stream. Disk-based video playback machines have been introduced such as video disks and more recently digital video disk machines. These machines may be generally characterized as providing a randomly accessed disk

25 allowing for the storage and playback of video signals. They are known as PVRs (for Personal Video Recorders) or DVRs (Digital Video Recorders) . The first generation of such machines accepted and generated analog video signals. Later generations had this functionality

30 integrated within set-top boxes, often handling digital MPEG based video signals. U.S. patent 5510889 of Kim, titled "Method of multi-speed recording-reproducing a video signal in digital video cassette recorder"; U.S. patent 6151443 of Gable et el., titled "Digital video and data recorder"; U.S. patent application 2003/0044166 of Haddad titled

"System for multiplexing video data streams in a digital video recorder and method of operating the same", and U.S. patent application 2004/0022313 of Kim titled "PVR- support video decoding system", all incorporated herein by reference, describe state of the art recording systems and methods. U.S. Patent 5,241,428 of Goldwasser et al . titled "variable delay video decoder", which is incorporated herein by reference, describes a video recording and playback device. The described system provides for simultaneous playback and recording of video signals on a randomly accessed recording medium. By allowing simultaneous recording and playback of video signals and by allowing for random access of the recording medium, additional functionality may be provided beyond that realized by a video tape recording machine. While video disks that process analog video signals in their inputs contain an analog to digital converter and a compression element that can be set to produce a digital bit stream of low enough bit-rate to suit both the storage and the visual quality requirements, digital video recorders process a video signal that is already digitized and compressed. The resulting visual quality of which is typically very high, but the employed bit- rate will be high typically accordingly, as suitable for a broadcasting application. Thus, what is needed is a method to provide more flexibility in providing a better trade-of between storage requirements and visual quality of the compressed video data.

SUMMARY OF THE INVENTION A method for providing a trans-rated video stream , the method includes: trans-rating, at a tape-less digital video recorder, a received video stream to provide a trans-rated video stream; and providing the trans-rated video stream. A computer readable medium having code embodied therein for causing an electronic device to perform the stages of: trans-rating, at a tape-less digital video recorder, a received video stream to provide a trans- rated video stream; and providing the trans-rated video stream. Conveniently, the trans-rating is slower than a process of receiving the video stream. Conveniently, the method further includes replacing a previously received video stream by a trans-rated video stream. Conveniently, the trans-rating is performed by a limited capability processor. Conveniently, the method includes storing the received video stream at a random access storage device. Conveniently, the method involves executing at least a portion of the trans-rating in parallel to the storing the trans-rated video stream. A method for extending a recording time of a tape- less digital video recorder, the method includes: receiving a video stream; and trans-rating the received video stream, whereas at least a portion of the video stream is stored at a random access medium prior to being trans-rated. A computer readable medium having code embodied therein for causing an electronic device to perform the stages of: receiving a video stream; and trans-rating the received video stream, whereas at least a portion of the video stream is stored at a random access medium prior to being trans-rated. Conveniently, the trans-rating is slower than a process of receiving the video stream. Conveniently, the method further includes replacing a previously received video stream by a trans-rated video stream.

Conveniently, the trans-rating is performed by a limited capability processor. A method for providing a trans-rated video stream , the method includes: determining to record a certain video stream at a tape-less digital video recorder; trans-rating the certain video stream to provide a trans-rated video stream, and replacing a previously received video stream by a compressed video stream. A computer readable medium having code embodied therein for causing an electronic device to perform the stages of: determining to record a certain video stream at a tape-less digital video recorder; trans-rating the certain video stream to provide a trans-rated video stream, and replacing a previously received video stream by a compressed video stream. Conveniently, the trans-rated video stream originated from the previously received video stream. Conveniently, the trans-rated video stream originated from a video stream other than the video stream it replaces. Conveniently, the trans-rating is performed by a limited capability processor. Conveniently, the trans- rating is slower than a process of receiving the video stream. Conveniently, the stage of replacing is responsive to vacant storage space. A tape-less digital video recorder that includes: a random access memory unit adapted to store trans-rated video streams, a processor adapted to trans-rate a received video stream being stored in the random access memory unit; whereas a trans-rated video stream replaces a previously stored video stream. Conveniently, the processor executes the trans-rate at a speed that is slower than a reception rate of the video stream. Conveniently, the recorder is further adapted to replace a previously received video stream by a trans-rated video stream. Conveniently, the processor has limited computational capabilities. A tape-less digital video recorder that includes: a random access memory unit; and a processor adapted to determine to record a certain received video stream, to trans-rate the certain received video stream to provide a certain trans-rated video stream, and to control a replacement of a previously received video stream by the certain trans-rated video stream. Conveniently, the processor executes the trans-rate at a speed that is slower than a reception rate of the video stream. Conveniently, the processor has limited computational capabilities. Conveniently, the recorder is adapted to execute at least a portion of the trans- rate in parallel to a storage of the trans-rated video stream in the random access memory unit.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the drawings in which: Figures 1-2 illustrate tape-less digital video recorders (DVRs) , according to various embodiments of the invention; and Figures 3-5 are flow charts of methods for extending the recording time of a DVR, according to various embodiments of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS The illustrated methods and devices extend the effective recording time of a tape-less digital video recorder by processing the digital video signal and reducing its bit-rate. A tape-less recorder is a recorder that does not record video streams on a tape. Such a recorder has another type of storage unit, such as a random access memory unit, memory medium. Said medium can include optical storage means, magnetic storage mediums (other than tape) , electrical storage mediums and the like. The term "compression" as used in relation to the following drawings means trans-rating. This the compression process is aimed to reduce the bit rate of a compressed (trans-rated) video stream. The video stream can be processed by a processor having limited processing capabilities, as the compression does not have to be executed in real time but rather during time gaps between the recording of the video stream and future viewing of the stream. Usually these time gaps are quite long, thus allowing to reduce the temporary computational load on the processor. Thus, video streams can be processed by processors that do not have the computational power to perform real time compression schemes. Figure 1 illustrates a DVR 100 that is connected to a display such as user interface 106, according to an embodiment of the invention. DVR 100 receives a compressed input video stream 105. This compressed input video stream 105 can be provided over various mediums and be modulated in various manners. Typically, compressed video streams are received over a satellite QPSK based front end, or a cable QAM based front end. DVR 100 includes processor 101 that receives the compressed input video stream 105. The processor 101 is connected to video storage unit 102 (also referred to as recording medium) , to program logic memory 103, to a video de-compressor 104, and to a user interface 106. The processor 101 may be any of a plurality of commercially available processors. These processors include many processors that are manufactured by many vendors. For example, processor 101 can belong to the

Pentium™ processor family of Intel™, it can be an ARM™ processor, a Motorola PowerPC™ processor, a STMicroelectronics ST20 family processor, a Texas Instruments processor such as the TI 320C5000, and the like. Processor 101 conveniently executes a code that is stored within program logic memory 103. This code can be executed to allow various DVR operations such as but not limited to a fast forward operation, a rewind operation, and the like. Processor 101 can also implement a trans- rating operation. Conveniently, video storage unit 102 is a high capacity, random access recording medium such as a hard disk. By using a random access recording medium the user can perform various operations in parallel, such as simultaneously recording and performing a playback of video signals. Thus, a user may view a program as it is being recorded and take advantage of the rewind, pause and fast forward capabilities of the DVR. According to another embodiment of the invention the video storage unit 102 can include a sequential recording medium. The compressed video stream can be provided over various networks and infrastructures, including but not limited to, cable network (such as Hybrid coax fiber networks), wireless transmission (using over-the-air broadcast) , satellite link and xDSL. According to various embodiments of the invention the DVR 100 can receive inputs from multiple video sources. The output video stream 107 provided from DVR 100 is usually sent to a user interface device, such as interface 106, that can be a television but the output video stream 107 can be sent from the de-compressor 104 to another device such as another DVR (not shown) . The video de-compressor 104 is adapted to de- compress video streams and provide an output video stream 107. Any commercially available compression technology may be utilized including by way of example MPEG 2 and MPEG 4. It is noted that the output video stream 107 can be provided to the user interface 106 from de-compressor

104 or can be provided from other components of DVR 100, such as the processor 101. Figures 1 and 2 illustrate a user interface 106 that is connected to processor 101, but this is not necessarily so. According to an embodiment of the invention processor 101 directs input video stream 105 from selected shows (programs) to the storage medium 102, to be retrieved later on for viewing by the user of the DVR 100 after de-compressing the video by de-compressor 104. According to another embodiment of the invention processor 101 applies a trans-rating algorithm and reduces the bit rate of the input video stream. This real time trans-rating scheme reduces the storage space required for storing the video stream thus increases the recording time of the DVR 100. DVR 100 can use any known trans-rating scheme. For example, an MPEG compliant scheme can include re-quantizing DCT coefficients. The compression ratio of the trans-rating operation can be about 1:2, but this is not necessarily so. Said ratio usually provides a reasonable visual quality video stream. That is because the original compressed video signal originated from a broadcast signal, that typically is set to use a high bit-rate to optimize the visual quality. However, for a personal video recording, typically a lesser quality is still acceptable, and the resulting storage time increase is more important. Figure 2 illustrates a DVR 200 that is connected to a display such as user interface 260, according to an embodiment of the invention. DVR 200 includes processor 201 that receives a compressed video stream from compressor 205, and also includes a video storage unit 202 (also referred to as recording medium) , program logic memory 203, a video decompressor 204, and a user interface 206. DVR 200 differs from DVR 100 of figure 1 by having a compressor 205 that receives non-compressed video streams. DVR 100 receives compressed video streams thus does not include such a compressor. Compressor 205 usually includes hardware components. It can be set to compress at various operating points (compression parameters) , which gives the flexibility of trading visual quality with storage efficiency. The compressor 205 of DVR 200 allows DVR 200 to compress the input video stream in various manners. The controller 201 has the flexibility to set the compressor 205 to any required operating point so as to satisfy the contradicting requirements of high compression and high visual quality, similar to the SP/LP option typically found in analog consumer Video Cassette Recorders. Figure 3 is a flow chart of a method for extending a recording time of a tape- less digital video recorder, according to an embodiment of the invention. Method 300 includes real time trans-rating. Method 300 starts when a new program (show) begins. Stage 301 checks if the new program should be recorded (if it meets a certain predefined recording criterion) . If the program should be recorded stage 301 is followed by stage 304, else method 300 waits to receive a new program and once said program is received stage 301 is repeated. Stage 304 includes checking whether the video storage unit (such as unit 102 or 202) has vacant space for storing the new program. If the answer is negative the process selects an older program to be removed from the storage. Else, stage 304 is followed by stage 308 of performing trans-rating. Stage 306 is also followed by stage 308. Stage 308 is followed by stage 309 of storing the trans-rated video stream. Figure 4 is a flow chart of method 400 for extending a recording time of a tape-less digital video recorder, according to an embodiment of the invention. Method 400 includes a trans-rating process 430 and a storage process 420. An input video stream is first stored in a video storage unit and then retrieved, trans-rated in an offline process, and eventually replaces the original video stream. Method 400 can be executed by a processor that does not have enough computational capability (or vacant computational resources) to perform real time trans- rating. In some cases a multitasking processor can allocate only a portion of its capabilities to execute certain tasks such as trans-rating. The recording process 420 includes stages 401, 404, 406 and 408 that are analogues to stages 301, 304, 306 and 309 of Figure 3 and require no further explanation. The trans-rating process 430 is executed off-line, or at least partially off-line. It starts by stage 409 of determining if the program needs to be trans-rated. The determination can be responsive to the presence of a complete video stream which was not previously trans- rated by method 400. If the answer is positive stage 409 is followed by stage 412 of retrieving the video stream from the video storage unit, stage 413 of trans-rating the program, stage 414 of storing the trans-rated program and stage 415 of deleting the program (original program) from which the trans-rated program originated. Figure 5 is a flow chart of method 500 for extending a recording time of a digital video recorder, according to an embodiment of the invention. Method 500, as well as method 400, includes off- line trans-rating. Method 500 differs from method 400 of Figure 4 by postponing the deleting (usually by overwriting) the original program to a time when the video storage unit is full. This postponing allows viewing the higher quality original program as well as the trans- rated program during a certain period. Method 500 includes a recording process 520 and a trans-rating process 530. The trans-rating process 530 includes stages 513, 516, 517, 518 and 519 that are analogues to stages 409, 412, 413, 414 and 415 of Figure 4. The recording process 520 starts when a new program (show) begins. Stage 501 checks if the new program should be recorded (if it meets a certain predefined recording criterion) . If the program should be recorded stage 501 is followed by stage 504, else the recording process 520 waits to receive a new program and once said program is received stage 501 is repeated. Stage 504 includes checking whether the video storage unit (such as unit 102 or 202) has vacant space for storing the new program. If the answer is positive stage 504 is followed by stage 512 of recording the new program. If the answer is negative (there is not enough vacant space) stage 504 is followed by stage 506 of checking if any original bit-rate show (not being trans- rated by process 500) is still stored in the video storage unit. If the answer is positive stage 506 is followed by stage 511 of removing the original program and jumping to stage 512. Otherwise, one of the older trans-rated programs is selected to be removed during stage 509. The benefit of deferring the erasure process of the high bit-rate shows is that if the user indicates his desire to watch a show soon after it was recorded, before the original show was deleted, the DVR can display the original show which has not been degraded by the trans-rating process. Stage 509 is followed by stage 512. Thus, what has been disclosed is an improved way of using a digital video recorder by implementing a trans- rating process, either on the fly or in offline mode. Variations, modifications, and other implementations of what is described herein will occur to those of ordinary skill in the art without departing from the spirit and the scope of the invention as claimed. Accordingly, the invention is to be defined not by the preceding illustrative description but instead by the spirit and scope of the following claims.

Claims

WE CLAIM

1. A method for providing a trans-rated video stream , the method comprising: trans-rating, at a tape-less digital video recorder, a received video stream to provide a trans-rated video stream; and providing the trans-rated video stream.

2. The method of claim 1 whereas the trans-rating is slower than a process of receiving the video stream.

3. The method of claim 1 further comprising replacing a previously received video stream by a trans-rated video stream.

4. The method of claim 1 whereas the trans-rating is performed by a limited capability processor.

5. The method of claim 1 comprising storing the received video stream at a random access storage device.

6. The method of claim 1 wherein executing at least a portion of the trans-rating in parallel to the storing the trans-rated video stream

7. A method for extending a recording time of a tape- less digital video recorder, the method comprising the stages of: receiving a video stream; and trans-rating the received video stream, whereas at least a portion of the video stream is stored at a random access medium prior to being trans-rated.

8. The method of claim 7 whereas the trans-rating is slower than a process of receiving the video stream.

9. The method of claim 7 further comprising replacing a previously received video stream by a trans-rated video stream.

10. The method of claim 7 whereas the trans-rating is performed by a limited capability processor.

11. A method for providing a trans-rated video stream , the method comprising: determining to record a certain video stream at a tape-less digital video recorder; trans-rating the certain video stream to provide a trans-rated video stream, and replacing a previously received video stream by a compressed video stream.

12. The method of claim 11 whereas the trans-rated video stream originated from the previously received video stream.

13. The method of claim 11 wherein the trans-rated video stream originated from a video stream other than the video stream it replaces.

14. The method of claim 11 whereas the trans-rating is performed by a limited capability processor.

15. The method of claim 7 whereas the trans-rating is slower than a process of receiving the video stream.

16. The method of claim 1 whereas the stage of replacing is responsive to vacant storage space.

17. A tape-less digital video recorder comprising: a random access memory unit adapted to store trans-rated video streams, a processor adapted to trans-rate a received video stream being stored in the random access memory unit; whereas a trans-rated video stream replaces a previously stored video stream.

18. The recorder of claim 17 wherein the processor executes the trans-rate at a speed that is slower than a reception rate of the video stream.

19. The recorder of claim 17 further adapted to replace a previously received video stream by a trans-rated video stream.

20. The recorder of claim 17 wherein the processor has limited computational capabilities.

21. A tape-less digital video recorder comprising: a random access memory unit; and a processor adapted to determine to record a certain received video stream, to trans-rate the certain received video stream to provide a certain trans-rated video stream, and to control a replacement of a previously received video stream by the certain trans-rated video stream.

22. The recorder of claim 21 wherein the processor executes the trans-rate at a speed that is slower than a reception rate of the video stream.

23. The recorder of claim 21 wherein the processor has limited computational capabilities.

24. The recorder of claim 21 adapted to execute at least a portion of the trans-rate in parallel to a storage of the trans-rated video stream in the random access memory unit.

25. A computer readable medium having code embodied therein for causing an electronic device to perform the stages of: trans-rating, at a tape-less digital video recorder, a received video stream to provide a trans- rated video stream; and providing the trans-rated video stream.