JP4325194B2 - Apparatus and method for managing access to storage medium - Google Patents

Description

  The present invention relates to an apparatus and method for managing access to a recording medium containing a set of digital broadcast data, and further to a system including such an apparatus.

  More generally, the present invention relates to multimedia.

  A set of digital broadcast data recorded on a direct access recording medium (CD, DVD, hard disk) generally has navigation information in addition to broadcast information, and the navigation information is at least one position from the recorded broadcast information. Can be obtained. This navigation information can identify at least some of the access units that make up the broadcast stream, to access each group of access units on the storage unit individually or to access a group of access units in order to retrieve them Can do. These navigation data may be transmitted with the broadcast stream or may be generated locally within the system by analyzing the broadcast stream.

  A set of digital broadcast data composed of a broadcast stream and navigation information may be a data structure that groups access units, allowing random access to each access unit or group of access units. This structure is referred to in this application as an enriched multimedia structure.

  “Broadcast information” is understood as any information distributed from a recording medium directly to a broadcast device (television, audio system, etc.) or over a transmission channel. Broadcast information relates, for example, without limitation, to video and / or audio signals, but also to other types of signals. In general, an “object” refers to an element or group of elements that make up a broadcast stream. “Direct access recording medium” refers to any information medium that allows direct positioning in read and write modes, either at any location on the medium or at a specific access location.

  Actually, for example, in the case of an audiovisual stream compressed in accordance with an MPEG standard such as MPEG-2 (the acronym for “Motion Picture Expert Group”), a packet of the basic stream type is recorded and stored in a hard disk or HDD (“hard disk Known as PES (Packetized Elementary Stream) or Transport Stream packet or TS type on drive "). In this case, the object can refer to an MPEG image, a group of MPEG images, a PES packet or an MPEG audio frame or a set of multiplexed TS packets.

  In systems where the broadcast stream is read and stored in a storage device such as a hard disk before being sent to the MPEG decoder, for example a digital video decoder, the user wishes to have the possibility to use a special display mode. . The special display mode (or “trick mode”) can consist of a playback mode, slow motion or image pause, especially in a fast forward or fast reverse direction.

  Displaying video sequences encoded in MPEG format in reverse order is a difficult problem. This is because, according to the MPEG format, the access unit that builds the MPEG video stream is encoded by referring to the previously transmitted object. In practice, the access units are transmitted in their decoding order because they are eventually displayed in a different order.

  The extended multimedia structure allows analysis of the broadcast multimedia content it represents and processing to implement a special display mode.

  According to known systems, proper processing of an EMS (enhanced multimedia structure) containing video can display its content in the forward or backward direction at an accelerated or slow speed. Accordingly, all display modes conventionally available on video recorders are realized.

Investigations regarding this type of processing show that access to broadcast data within these trick modes can have the following properties:
• The access unit is read non-sequentially.
They are not all read out.
They are not read out in the correct order.
A specific access unit is read out several times at a moment when there is no gap within a certain period.

Conventional methods for accessing and transferring streams use a buffer memory that is managed in a circular fashion using a system for pseudo-continuous reading of storage media. These methods indicate that they are poorly adapted to the trick modes described above. Because
Continuous reading reads more than necessary objects,
There is a troublesome disconnection related to buffer circularity and its discontinuous filling with non-constant stream read instructions,
If it is desired that one access unit be maintained in the circular buffer longer than the other, it is not possible to make the buffer unrelated to an access unit that is not used but loaded later.

  The present invention therefore provides an apparatus that can solve the above-mentioned drawbacks by accessing the stream for each image and at the same time optimizing access to the recording medium in order to avoid wasteful use of memory. There is to do.

Therefore, the present invention provides an apparatus for managing access to a recording medium including a set of digital broadcast data having broadcast information and navigation information.
A cache memory for temporarily storing broadcast information read from the recording medium and a data structure including at least data included in navigation information related to the broadcast information;
Means (20) for managing broadcast information existing in the cache memory (6), wherein the broadcast information and the data structure related thereto are determined according to information contained in different data structures stored in the cache memory. And a device capable of being erased.

  The device is called an image cache.

  The image cache must provide the objects needed by the client by making it available to the client in memory. The image cache is therefore responsible for managing a dedicated cache memory, loading new objects into it from the recording medium and deleting old objects from it.

  The cache memory is substantially a memory area smaller in size than the recording medium, but has a memory-specific access mode and time, and in this case is faster than the recording medium.

  The cache memory of the image cache is a memory area in which broadcast information is temporarily stored. This memory area may simply be a partition of the system's shared memory. The broadcast information is preferably digital data coming from a recording medium, and is intended for a broadcast device or a transmission channel. These broadcast data are generally encoded according to standards such as MPEG-2 and represent access units or groups of access units.

  The management means may simply be software that is executed and shared on a computing unit available in the system. It can also be realized as hardware by an ASIC cell (acronym for “Application Specific Integrated Circuit”). This management means reads the new object from the recording medium and deletes the old object already existing in the cache memory in order to ensure that the requested object is present in the cache memory. To decide.

  A data structure for image cache management lists at least identifiers of broadcast information stored in memory and parameters specific to the storage (eg, address and size). It makes it possible to know which broadcast data is present in the cache and to access these data to retrieve them.

  According to one characteristic, the data structure for broadcast information includes at least data obtained from the type of broadcast information, a time base criterion and an index. The data structure thus contains data that allows the image cache to manage the images it contains in an effective manner.

  These parameters allow for preferred management of broadcast data residing in the cache. This is because when a new object is needed for decoding, the cache memory management means must replace the broadcast data with data read from the recording medium corresponding to the object requested by the decoder. is there.

  In one preferred embodiment, the broadcast information is preferably audio and / or video and is intended for trick mode.

  The present invention is particularly effective in this case compared to known techniques, especially in the case of reading in the reverse playback mode, where the use of the circular buffer does not allow the access units to be drawn out in a different order from the input order. It is effective. Furthermore, the data structure associated with the broadcast information can be loaded with an appropriate image.

  According to another feature, when the management means receives the broadcast information request, the management means, based on the relevant navigation information or the information present in the relevant data structure, and the trick mode, the broadcast information present in the cache memory and the related information. The digital broadcast data is read from the recording medium.

  Therefore, when a new object is needed for decoding, the cache memory management means replaces the broadcast data with data read from the recording medium corresponding to the object requested by the decoder.

  According to the first embodiment, the management means includes means for weighting the broadcast data, the weighting means based on information on the data structure associated with the broadcast information to be weighted and / or in trick mode. Weight broadcast information based on it.

  The weighting means uses a weighting standard such that broadcast data with little or no deletion and subsequent reloading is erased faster than others.

  The management means therefore effectively determines the old object present in the cache memory to delete the object, and frees up a memory area where it can receive the new object requested by the client, Ensure that a minimum number of objects are loaded from the storage unit.

  For example, in the case of an MPEG-2 video stream, the object is an image, and the image to be deleted from the cache is determined based on the requested image index and display instruction. In the forward playback mode, it is the image with the smallest index that is removed from the cache. In the reverse playback mode, it is the image with the largest index to be deleted.

  However, due to cache memory fragmentation, it may happen that the deletion of a single object is not sufficient to free up space in the cache for a new object to be loaded.

  At that time, it may be effective to continuously delete the broadcast data stored at the address adjacent to the previously deleted broadcast data from the cache memory. This second iteration of freeing memory can ensure that these new deletions of objects actually increase the size of the free monolithic memory area. It can then be estimated that a minimum number of objects are deleted from the cache memory in this way in order to free up the necessary memory space.

  These display modes are currently used in many video systems.

  In contrast, the present invention is a method for accessing a recording medium including a set of digital broadcast data, wherein the set of digital broadcast data preferably includes broadcast information and navigation information that are audio and / or video. And the broadcast data relates to an access method capable of targeting a trick mode.

According to the invention, the method comprises:
Temporarily storing the broadcast information read from the recording medium (8) and the data structure (50) related to the broadcast information in the cache memory (6);
Erasing the broadcast information and its associated data structure according to information contained in different data structures (50) stored in the cache memory (6).

  The invention also relates to a video decoding device comprising a device for managing access to a recording medium as described above.

  The invention also relates to a television receiver comprising a device for managing access to a recording medium as described above.

  The previously cited advantages for the device apply equally to the method according to the invention, the video decoding device and also the television receiver.

  The invention will be better understood and other features and advantages will become apparent in the following description of non-limiting embodiments with reference to the accompanying drawings, in which:

  The digital television receiver decoder of FIG. 1 has an error correction circuit 2 to which a signal is sent by a tuner and an analog / digital converter (not shown). The corrected digital signal is transmitted to the transport stream demultiplexer filter 4. The demultiplexer filter 4 is connected to the central communication bus 3 of the receiver 1. Its role is to select transport stream packets in the incoming new data stream and send them to the various applications at the receiver. For that, it has a filter programmed by the microprocessor 11.

  In order to record the MPEG stream, the receiver has a hard disk 8 connected to the bus 3 by means of an interface 7, for example an EIDE interface. The integrated memory 6 is shared by all processes of the receiver. This memory in particular has a memory area allocated for the image cache.

  In order to decode the stream, the receiver 1 also has an audio decoder 12 and a video decoder 13 connected to the central bus 3. The second transport demultiplexer filter 9 can filter the audio and video components of the recorded transport stream coming from the EIDE interface and can forward them to the memory 6 or the decoders 12 and 13 . Depending on the recording mode, the layer of the transport stream may or may not be removed beforehand.

  Specifically, the navigation information is recorded for each video access unit stored on the disk for recording, the image type (I, P or B), its time base reference, the corresponding image position, and / or group of images. With links and details.

  An example of a navigation information structure is European Patent Application No. 00400941.1, filed April 5, 2000 by Thomson Multimedia, "Method and apparatus for decoding a digital video stream with pseudo-header insertion in a digital video system". It is stated in.

  FIG. 2 is a diagram of the software model of the receiver 1. It has the following elements:

Display monitoring program (14)
This software module has the role of general control of the decoding method. Depending on the display method (forward / reverse, slow / fast), this module indicates which images should be transferred, decoded or displayed.

  For example, if the display mode is fast reverse reproduction with normal speed multiplied by X, this module determines which image should be displayed (I, B, P). However, in the case of P or B type images, other images to be decoded are determined in advance. This method is performed recursively.

  The display monitoring program accesses the navigation information via the navigation information access management program.

  Based on the recursive decoding algorithm, the display monitoring program schedules the image cache to provide it with the memory address 6 of the video access unit that it is desired to transfer to the MPEG video decoder 13.

Navigation information access management program (19)
The display monitoring program requires navigation information on the recorded stream. This information is stored in the hard disk 8. The navigation information access management program has a role of collecting information from the hard disk 8 and providing it to the display monitoring program when requested by the display monitoring program.

Image cache management program (20)
Each image to be decoded (to be displayed or not displayed later) must be temporarily loaded into the memory 6 and then transferred to the MPEG video decoder 13. All the information necessary to access the compressed content is provided in the navigation information. The image cache further has a role of transferring image data identified by the display monitoring program from the hard disk to the memory 6 if necessary. For each image to be decoded, the image cache displays the parameters necessary to transfer the image from the memory 6 to the decoder 13, and in particular the address of the image in the memory and its size. Required by the program.

  The image cache management program 20 implements the flowchart of FIG. When data must be erased from the cache memory (6) to free up memory space for storing new images, it takes into account the relevant data structure parameters as well as the requested current special display mode, These various parameters are weighted to determine the image to be deleted.

・ Video decoding monitoring program (15)
When the video decoder receives and identifies a new video access unit, the video decoder informs the video decoding monitoring program. The video decoding monitoring program receives in advance a complete command that schedules and designates this accurate image decoding and / or display via a queue coming from the display monitoring program. Based on this command, the video decoding monitor program programs the decoding of this detected new image, and if the image is to be displayed, this image should be displayed and how. Tell the video display management program what to do (in order of interlaced frames).

  The MPEG Video Decoding API (Application Program Interface) (16) allows for specific types of examination and decoding of individual images and operations related to any display. In particular, the API can receive an order to decode individual images and then an order to display them at a given time and a fixed number of image intervals, or no display at all.

  The display monitoring program requests the transfer of a new image when necessary, and waits until the transfer is completed before sending another request. The completion of the transfer is signaled there by the image cache management program.

  FIG. 3 represents an expanded multimedia structure. The extended multimedia structure is composed of a digital broadcast stream 60 and navigation information related to various access units 61, 62, 63, 64 constituting the broadcast stream 60.

  The digital broadcast stream 60 includes access units 61, 62, 63, and 64. Navigation information is associated with each access unit. Navigation information 71 and 81, 72 and 82, 73 and 83, 74 and 84 are associated with access units 61, 62, 63 and 64, respectively. This navigation information includes the size of the access unit, the address of the access unit and other parameters. The items of navigation information are also related to each other from one access unit to another. In practice, it is desirable to know what the preceding or following image is for a particular type of stream, eg MPEG2. This information is stored in association tables 81, 82, 83, 84, each associated with the access units 61, 62, 63, 64 and forming part of each extended multimedia structure.

  FIG. 4 shows a data structure (50) related to broadcast information stored in the cache memory (6).

  Each data structure 50 includes two types of information. The two types are information 52 unique to the image itself and information 51 on the address and size of the image in the cache memory. The address and size are information necessary for managing any cache memory. is there.

  Information present in the field 52 can effectively manage the cache memory. This information is, for example, the type of image, the time base reference of the image and the index of the image.

  In FIG. 5, in step E1, the display monitoring program requests a new image. The image cache then looks through the N rows of the cache at stage E2. If the test in step E3 has the required image in the cache, then step E10 is entered, otherwise step E4 is entered.

  In order to place the required new images in the cache, step E4 determines which images should be deleted from the cache. The selection of the image to be deleted takes into account the navigation information associated with the image, the trick mode and the data structure associated with the image. These criteria are weighted to determine the image to be erased.

  Once the image to be deleted is determined, the memory area corresponding to this image is deallocated in step E5.

  In step E6, instead of the deleted image navigation information, the necessary image navigation information is copied into the data structure of the cache. This information in particular gives the required image size.

  At step E7, a test is performed to find out if the space de-assigned at step E5 is sufficient to store the required images. If the size of the deallocated space is smaller than the size of the required image, at step E8, an additional image is deleted, which is preferably stored in memory in the area adjacent to the previously deleted image. It is remembered.

  Otherwise, if the deallocated memory space is sufficient to store the required image, step E9 is entered while the required image is loaded from the hard disk into the image cache.

  Next, step E10 is entered, where the detailed coordinates of the image in the memory 6 can be provided to the display monitoring program, and the display monitoring program can transmit the detailed coordinates of the image to the video decoder.

  In the case where the reverse playback mode is the special display mode, an exemplary path of data in the television decoder of FIG. 1 is described.

Consider that the cache size is fixed at 4 and that the cache contains the following four images:
Row A, image with index value 1234, internal image 0
Row B, index 1235 image, predicted image 3
Image of row C, index value 1238, predicted image 6
Row D, image with index value 1240, predicted bidirectional image 5
The image index 1240 is the last image used and requested by the trick mode monitoring program 14.

  Now, the monitoring program requests an image B4 (bidirectional image 4 that can be predicted) preceding the bidirectional image 5. The request from the surveillance program is to transfer the in-memory reference for the desired image descriptor to the image cache. The image cache can find the appropriate image index 1239 in the image descriptor and compare this index with the index of the image already in the cache, and the index is stored in memory in the data structure. . Scanning the data structure thus results in the image 1239 not being in the cache. Therefore, it is necessary to load the image 1239 into the cache, which requires some space to be freed.

  As an example, the weighting means may use an image index to perform weighting. Images with the largest index in reverse playback must be deleted. That is, here, the image is index 1240.

The data associated with the image in row D in the data structure is index 1240, bi-directional type, image number in GOP 5 (timebase reference), image size (11356) and image compressed data. Memory address. Therefore, first, the memory area used for the image of index 1240 is deallocated and the address of this area is given to the memory management program.

  The data associated with cache line D is then updated based on the new image descriptor in the navigation information. These data are index 1239, type B, time base reference 4, size 11356 bytes, and a meaningless address such as 0x00000, which is filled when the data is written to the cache.

  The memory area must be reserved so that the compressed data of this image can be stored there. The memory management program is then required to allocate 11536 bytes. If this assignment is successful, the management program returns to the address of the assigned area, for example 0 × AF000800. This address is then written to the data structure to replace the first address with a meaningless address.

  If the memory area freed by deleting the image at index 1240 from cache line D is not sufficient, it is necessary to delete additional images from the cache to free up more memory. It is possible to retrieve a cache line that uses a memory area adjacent to the area that was just unassigned, delete this line, and retry the assignment.

  The compressed data of the image is then loaded from the hard disk (recording medium) into a cache memory in a pre-allocated area. To access the image in the digital file during reading, the position of the first byte of this image in the file is used and this position is provided by the navigation information. This location, image size, and address to be loaded are transferred to a file management program that transfers data from the hard disk to the memory. When this transfer is completed, the digital data can be retransmitted from the cache memory to the MPEG video decoder.

  The image cache is then ready to process new requests. This request is logically a request for the predicted image 3, that is, the image of the index 1235 existing in the cache line B. With this image already in the cache, the cache transfers it directly to the MPEG video decoder and no reading of data on the hard disk is required.

  Images are loaded into the cache only once, thus facilitating execution. Operations in the video decoding apparatus are parallel. For example, when the cache is reading broadcast information from the disc, the preceding image is transferred to the MPEG video decoder, for example by using DMA type transfer driven by the processor 11. During this time, the decoder decodes the preceding image and the display displays yet another preceding image.

2 shows a diagram of a television decoder. Fig. 2 represents a diagram of some software models implemented for trick mode of the device of Fig. 1; 2 illustrates an example of an extended multimedia structure according to the present embodiment. 3 shows a data structure related to broadcast information stored in a cache memory. 7 shows a flowchart for loading a new image into the cache memory, realized by the management means.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Receiver 2 Error correction circuit 3 Central communication bus 4 Transport demultiplexer filter 5 Stream syntax analysis program 6 Cache memory 7 Interface 8 Hard disk 9 Transport demultiplexer filter 11 Microprocessor 12 MPEG audio decoder 13 MPEG video decoder 14 Display monitoring program 15 Decoding monitoring program 16 MPEG video decoder API
17 HDD Interface 18 File System 19 Navigation Information Access Management Program 20 Image Cache Management Program 50 Data Structure 51 Cache Line Descriptor 52 Stored Image Descriptor 53 Cache Line Index 60 Digital Broadcast Data 61, 62, 63, 64 Access unit 71, 72, 73, 74 Access unit descriptor 81, 82, 84 Related table

Claims (10)

In an apparatus for managing access to a recording medium including a set of digital broadcast data having audio or video data and navigation information,
A cache memory for temporarily storing audio or video data read from the recording medium and a data structure including at least data included in navigation information related to the audio or video data;
Means for managing audio or video data existing in the cache memory, wherein a plurality of data structures stored in the cache memory are read out and deleted according to the plurality of data structures stored in the cache memory; Means for selecting the audio or video data to be deleted, and deleting the selected audio or video data and the data structure related thereto;
Including
Data from the navigation information contained in the data structure, device characterized in that it comprises the type of each image of the video data. The audio or video data is subject to trick mode;
The apparatus of claim 1. When the management means receives a new audio or video data request,
If there is no free space in the cache memory, the selected audio or video data existing in the cache memory and the data structure related thereto are deleted,
Read new audio or video data and navigation information related to the new audio or video data from the recording medium, and load the new audio or video data and data structure related to the cache memory,
Use the trick mode type to select audio or video data to be erased from the cache memory.
The apparatus of claim 1. The management means includes means for weighting the audio or video data,
The weighting means weights the audio or video data based on the data structure related to the audio or video data to be weighted or based on the type of trick mode,
The weight set by the weighting means is used by the management means for selecting audio or video data to be deleted from the cache memory.
The apparatus according to any one of claims 1 to 3. The management means deletes audio or video data stored in a storage area adjacent to the empty space in the cache memory when the empty space in the cache memory is not sufficient,
Apparatus according to any one of claims 1 to 4. A method of accessing a recording medium including a set of digital broadcast data, wherein the set of digital broadcast data includes audio or video data and navigation information, and the audio or video data is of various types. In a method that is subject to trick mode,
Temporarily storing, in a cache memory, audio or video data read from the recording medium and a data structure including at least data included in navigation information related to the audio or video data;
A data structure stored in the cache memory is read out, audio or video data to be deleted is selected according to the data structure stored in the cache memory, and the selected audio or video data and a data structure related thereto are selected. Erasing, and
Including
Data from the navigation information contained in the data structure, the method comprising the type of each image of the video data. When new audio or video data recorded on the recording medium is requested, if there is no free space in the cache memory, the selected audio or video data existing in the cache memory and the data structure related thereto are deleted, and new audio Alternatively, digital broadcast data having video data is read from a recording medium, the new audio or video data and a data structure related to the new audio or video data are loaded into a cache memory,
Use the trick mode type to select audio or video data to be erased from the cache memory.
The method of claim 6. Audio or video data is weighted based on the data structure related to the audio or video data or based on the type of trick mode, and the weight set for the audio or video data is deleted from the cache memory. Use for selection,
The method according to claim 6 or 7. A video decoder;
A video decoding apparatus comprising: the apparatus according to any one of claims 1 to 5, which is upstream of the video decoder.   A television receiver comprising the apparatus according to claim 1.

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