KR100987655B1 - Characteristic point informationcpi for multilayer video - Google Patents

Abstract

A method of generating feature point information (CPI) for multilayer encoded audio / video data includes generating a CPI file. The CPI file includes at least point type corresponding to at least one point in the clip, presentation time corresponding to a point in the clip, and one or more offset points corresponding to points in the base layer and one or more enhancement layers of the clip. The points identified by the offsets in the base and enhancement layers of the clip all correspond to the same point in the clip.

Description

CHARACTERISTIC POINT INFORMATION (CPI) FOR MULTILAYER VIDEO}

FIELD OF THE INVENTION The present invention generally relates to video encoding, and more particularly to multilayer video encoding.

In portable storage, multilayer encoded video offers many advantages. In devices with small screens and low power, only the base layer is retrieved and displayed. In devices with larger screens and more power, both the base layer and one or more enhancement layers can be retrieved and displayed. Although the multilayer approach is most effective in portable devices such as small-form-factor optical discs ("SFFOs"), it can also be used to realize a fluid storage approach in fixed devices.

The description below considers in particular audio / video ("A / V") devices operating according to the MPEG standard (ISO / IEC 11172 for MPEG-1, and ISO / IEC 13818 for MPEG-2), although those skilled in the art will appreciate the MPEG standard. It will be appreciated the applicability to other A / V coding schemes that do not comply with

A clip refers to all or part of an audio / video (A / V) file or stream, and may be multiplexed. (Clip files may be more generally characterized as content files.) The multiplexed streams that are part of them are all aspects, for example in the case of MPEG-2 multiplexed streams conforming to the MPEG-2 program stream or transport stream specification. Conforms to the definition specification in. Decoding some elementary streams into a multiplex may need to start at a later address later in the clip, since a partial access unit may exist at the beginning and end of the clip. The presentation may even need to start in a later presentation unit.

Each clip is stored in its own real-time file. Physical allocation of real-time files on disk ensures a continuous supply of data for reading and writing. Data portions within a clip may be shared between two or more clips using a data sharing mechanism defined in the file system. In general, an initial recording is made with a single clip, and the number of clips increases as the editing operation is performed.

Characteristic Point Information (CPI) generally refers to information used to indicate characteristic points in a clip or an information file. The feature point corresponds to the location of a particular data element in the clip file, for example a point that is considered to be of interest for a particular reason. For example, in a clip containing video stream data, feature points are used to mark the beginning or end of a particular video access unit. CPIs are generally used to determine the location of related data elements within a clip without having to read and parse the clip itself. Therefore, CPI is important for many different system operations.

Some examples of such operations include trickplay operations, interactive playback, and fast edit-like operations. During trick play operations such as fast playback and fast rewind playback of clips containing video stream data, the stream is not perfectly read and decoded. Instead, only selected portions of the stream are read and decoded. The selection of these parts is based on the CPI. For this purpose, the CPI contains, for example, feature point information indicating the position of the image data.

In the case of interactive playback, the user may require that playback begin at some specific time location within the clip rather than at the beginning of the clip. In this case, the CPI is used to find the data location for reading and decoding the location in the clip that matches this time location. For this purpose, the CPI may include, for example, a timestamp value for the associated audio and video access unit.

An important feature of fast edit-like operation involving clip truncation is that it creates a truncated version of the clip without actually touching any data in the clip itself. In general, this kind of operation references clipped versions of these clips and manipulates clip criteria to create new clips. Possible examples include splitting a clip into smaller clips, forming new clips by non-seamless editing connections, and the like. In all such cases, the CPI may be used to determine where the truncated version of the clip should start and / or end. Specification of feature points for a stream generally depends on the type and content of the stream.

In video recording systems such as HDDs and non-multi-layer environments, CPIs are extracted from the media and stored (eg, in RAM) to provide a mapping between the presentation time of the content and the location of the content on the disk. CPIs are stored in files separate from the actual audio / video ("A / V") content. In general, CPI is used to point to an I-frame in MPEG-2, but in general CPI is used to point to points of interest in the content, for example entry points or other key points. In existing systems without multilayer video, an entry in a CPI file is typically a point type such as an entry point (“I-frame”), a presentation time (“PTS”), and an offset or A / V in the A / V file. Defines an absolute address for a point in the V file.

Conventional multilayer encoded video includes a base layer and one or more enhancement layers. In general, the base layer is coded independently, and the data encoded within the enhancement layer complements the base layer data. Thus, the base layer may be decoded and used separately. However, in order to use the enhancement layer, the base layer and the enhancement layer must be decoded and used together. In general, smaller or older devices may only use the base layer at the time of playback of the clip, while larger and / or newer devices (with improved processing and / or resolution) may be used at the time of clip playback. An enhancement layer will be used, with the same level of quality improvement. The number of enhancement layers used depends on the device used for reproduction.

It is necessary to have CPI for both low quality and high quality encoding of the multilayer scheme. Therefore, an extended CPI scheme is required to consider multilayer video.

Thus, a method of generating feature point information (CPI) for multilayer encoded audio / video data is provided. In an aspect, the method includes generating a CPI file. The CPI file includes a point type corresponding to at least one point in the clip, a presentation time corresponding to a point in the clip, and one or more offset points corresponding to points in the base layer and one or more enhancement layers of the clip. The points identified by the offsets in the clip's base layer and the enhancement layer all correspond to the same point in the clip (most easily thought of as the same presentation time). Alternatively, the actual presentation time (or absolute memory location) corresponding to the points in the base layer and one or more enhancement layers of the clip may also be included.

In another aspect, the method includes generating a separate CPI file for the base layer and each enhancement layer. The CPI file for the base layer contains information about points in the base layer, and similarly the CPI file for the enhancement layer includes information about points in the corresponding enhancement layer. The CPI file for the enhancement layer may include only offset information and may use the point type and presentation time for the corresponding point in the base layer CPI file.

In still another aspect, the method includes generating a CPI file to include information about the base layer, and generating a separate additional CPI file to include information about each enhancement layer. The CPI file corresponding to a particular enhancement layer may include, for example, a pointer to the base layer as well as the enhancement layer and all sublayers.

These and other features of the present invention will become apparent to those skilled in the art from the following detailed description, taken in conjunction with the accompanying drawings, wherein like reference numerals refer to like parts.

1 illustrates a CPI scheme in one embodiment.

2 illustrates a CPI file corresponding to each layer in one embodiment.

3 shows a CPI structure with a separate CPI file for all enhancement layers in one embodiment.

1 is a diagram illustrating a CPI scheme in an embodiment. Briefly, in each clip or A / V file, there is an attached CPI file containing information about feature points in the clip file. The feature point (or "point") in the clip file has an entry in the CPI table structure that includes at least the point type (or implied if only one point type is possible), the PTS and the offset in the file.

Thus, at each feature point, several parameters are used. Thus, each entry 104 in the CPI file 102 may include a point type, a PTS, and one or more offsets. The point type may, for example, indicate that the point corresponds to the start position of the I frame. Points in the point type may also exist, for example, as a pair of start and end points of an I-frame. A single point may contain both start and end pointers, or may be considered two points. If all feature points include both start and end pointers, it is efficient to combine the start and end pointers for each point into a single point. If not all points contain start and end pointers, the use of start and end pointers by a particular point is acceptable.

PTS is a data parameter used in an entry in a CPI. In this case the PTS represents a well known presentation time in MPEG. For example, the PTS may be a 32-bit timestamp value that represents the presentation time of the I-frame. Such a parameter generally indicates a data field associated with the point. The exact syntax and semantics of the data fields depend on the type of point and are specified separately for each type. Thus, the point type and the point data parameter correspond to each other.

In addition, the offset contained in the entry of the CPI file corresponds to the position in each video layer. In particular, offset B identifies the location corresponding to entry 104 point in base layer 106, and offset 1 identifies the location of entry 104 point in enhancement layer 1 108a. The offset value included in the entry for each layer provides the offset in the file of the layer corresponding to the entry point. As is known in the art, an offset defines how far forward in the file, starting at a known starting point. In this case, starting at a known starting point and moving forward by an offset in the layer file results in a move to the point under consideration in the entry. Offsets are typically used in applications and are therefore translated to absolute addresses when accessing data in storage media (such as disks).

Thus, the offset contained in each entry provides the respective position in the file with respect to the base layer and the enhancement layer corresponding to the feature points of the entry. Alternatively, the absolute address of the corresponding location in each layer may be used in the entry instead of the offset. This allows the base layer and any enhancement layer for a point to be accessed using the entry for that point in the CPI file.

For free space on the disc, the user may delete the highest level of enhancement layer, for example "108n" in FIG. In such a case, some offset in the CPI file may no longer be valid because it may refer to the deleted file. Thus, the CPI file may also include an indication of a valid layer (indicated by the presence of a check mark for the valid layer in the entry of FIG. 1). Since the number of layers in the CPI file depends on the number of layers present at the time of recording, which can vary in units of recording, the CPI file structure may also include an indication of the number of layers referenced.

The entry 104 of the CPI file 102 of FIG. 1 can be further efficiently organized in a horizontal manner. For example, the PTS of each entry may contain an absolute time value. Alternatively, the PTS for every nth entry may be an absolute value and the PTS for subsequent entries in the CPI file may be associated with the final absolute value (referred to as "horizontal offset"). For example, the PTS may be every tenth entry that is an absolute value. In the nine entries in the CPI file followed by the last absolute PTS entry, the PTS may be provided as a horizontal offset to the last absolute PTS.

Other parameters in the entry of the CPI file can be configured in a similar manner. For example, offset B may be an absolute offset value in every tenth entry of a CPI file. In the nine entries in the CPI file followed by the last absolute offset value for offset B, offset B may be provided as a horizontal offset to absolute offset B. For example, entry n in CPI file 102 may include an absolute value of 1000 for offset B, and entry n + 10 includes the next absolute value 1100 for offset B. The intervening entries n + 1, n + 2, ..., n + 9 are the horizontal offset values 10, 20, ..., for offset B instead of the absolute values 1110, 1120, ..., 1190 for offset B. Has 90. Thus, when the application reads a parameter for offset B of entry n + 2, it retrieves horizontal offset 20 from the entry, for example, and determines offset B 1120 based on the absolute offset value for offset B in entry n. . Offset B, which is 1120, is then used as an offset to access the corresponding position in base layer 106 for entry n + 2.

The horizontal organization between entries in this CPI file may similarly be used for other parameters, further reducing the required memory without significant performance degradation. However, it should be noted that since the base layer and enhancement layer files have different lengths, the horizontal offset between CPI entries for one parameter cannot be used for the other parameter. For example, the horizontal offset for offset B in entry n + 2 (20 in the example above) cannot generally be used as the horizontal offset for offset 1 in entry n + 2, which is the base layer and the first enhancement. This is because the layer piles will have different lengths.

Returning to the focus of the "offset" as shown in FIG. 1, that is, as a pointing to a location in the base layer and the enhancement layer corresponding to a point in the entry, the CPI file structure of FIG. 1 is generic, eg named. It can be applied to other existing CPI schemes using a naming scheme. For example, in a particular system, the relationship between CPI and A / V content is based on the filename, or more specifically the filename extension. For example, file.clpi may represent file clip information and file.m2ts may represent a file MPEG-2 transport stream. In multilayer video, this approach is for example file.clpi for file clip information, file.av for file base layer A / V data, file enhancement. File1.av for A / V data, and file enhancement. 2 can be extended to include file2.av for A / V data. In this multilayer application, file.clpi is modified to include the layer offset for each entry, as shown in FIG. Thus, each feature point entry in file.clpi includes a base layer offset (offset B) corresponding to file.av, a first enhancement layer offset (offset 1) corresponding to file1.av, and the like.

In addition, the foregoing description assumes that each enhancement layer has feature points at the same time position, all of which are stored in a CPI entry. Some of the offset parameters may be omitted for some entries for higher level layers in order to reduce the size of the CPI file. For example, the offset for the first enhancement layer may only be included in every second or third entry. However, this will limit the feature points that can be used in certain functions, such as high quality trick play.

In another aspect, the CPI may be stored separately for each layer on the disk, so that for each file of layered encoding there will be a corresponding CPI file. 2 shows a CPI file in one embodiment corresponding to each layer. The base layer file 206 is spaced apart from the enhancement layers 208a and 208b and has a corresponding CPI file (CPI FileB 202). As is the case with the Nth enhancement layer Enh N 208b file whose corresponding CPI file is shown as CPI FileN 210, the first enhancement layer Enh 1 file 208a is itself a CPI file (CPI File1 204). } Has

There are many advantages when using separate CPI files for each file of layered encoding. The enhancement file cannot be deleted without the need to notice the deletion in the CPI file for the other layer. In addition, there is no need to read the CPI file for the unused enhancement layer. The separate CPI file corresponding to each layer eliminates coordination and / or potential problems with the CPI file when one or more enhancement layers are deleted. For example, when one or more enhancement layers are deleted, the composite CPI file as shown in FIG. 1 then includes one or more invalid parameters in the entry for the enhancement layer just deleted. (As noted above, the indication of the invalid layer is included in the CPI at this time.) Also, if all CPIs are included in one CPI file, it may be necessary to read the complete CPI file even if only the base layer is being played. Can be.

In an aspect, similar file naming conventions described in the examples above may be used. For example, file.clpi can be used as a CPI file (202 in FIG. 2) for a base layer file, file1.clpi is a CPI file (204 in FIG. 2) for file enhancement 1 clip information, and file.av is CPI file (206 in FIG. 2) for file base layer A / V data, file1.av is file enhancement 1 CPI file (208a in FIG. 2) for A / V data, and fileN.av is file enhancement NA / It can be used as a CPI file (208b in FIG. 2) for V data.

In one case for the embodiment of FIG. 2, the point type and PTS are duplicated for each CPI file 202, 204, 210. (Each CPI file also includes an offset value for each layer.) In another aspect, duplication of the point type and PTS in each CPI file can be avoided. Thus, the base layer CPI 202 may include the point type, PTS, offset B (for the base layer), and in each enhancement layer, the corresponding CPI file may have an entry that includes the offset for that layer. have. In this case, it is understood that entry n in the base layer CPI file corresponds to entry n in each enhancement layer CPI file. Also, the point type and PTS for entry n in the base layer CPI file apply to entry n in each enhancement layer CPI file. In this manner, the point type and the PTS do not need to be duplicated for each CPI file (ie, CPI File1 through CPI FileN).

Even if all the parameters for a point are not included in a single entry in a single CPI file (as in the embodiment of FIG. 1), once a separate CPI file is loaded into memory, for example, as shown in FIG. However, there is no performance penalty for using a separate CPI structure. Corresponding entries in the various CPI files can be easily accessed for the same point once loaded, where loading of separate CPI files in memory includes sequential concatenation of the CPI files. For example, if there are M CPI entries, the base layer CPI has an entry size A for feature point information, and the first enhancement layer CPI has an entry size B for feature point information, start at address S in memory. In order to access the entry for a particular point x from the combined CPI, the following operation can be performed:

x.Point Type = (S + A * x) .Point Type

x.PTS = (S + A * x) .PTS

x.Base Offset = (S + A * x) .Base Offset

x.Enh Offset = (S + A * M + B * x) .Enh Offset

Similarly, entries in the CPI file for multiple enhancement layers can be accessed with similar simple calculations. Thus, performance is not sacrificed by the storage of separate CPI files as described above on disk (or other media). Also, the horizontal offset used between the CPI entries described above applies equally well in the case of separate CPI files for each layer.

As noted, the operation assumes that the CPI file is loaded into memory so that the enhancement layer CPI file is directly from the base layer CPI file. However, if not, a new offset indicating memory distance between files may be included in the calculation.

It is implied that in the above structure, the number of entries in the base layer and the enhancement layer are both equal to M. However, the enhancement layer may include fewer feature points, for example one feature point for every two or three points in the base layer (corresponding to the frequency of subsampling). In such a case, if the number of CPI entries for the enhancement layer is M, every two or three points in the enhancement layer may be the same. This is an unnecessary use of memory. However, in this structure, as far as the frequency of subsampling is known and taken into account when modifying the operation, there is less for the enhancement layer (by eliminating adjacent two or three overlapping points in the enhancement layer). It is still possible to have an entry.

In another aspect, the CPI file may include points of all lower layers for the enhancement layer. This means that each CPI file is self contained and contains pointers to the current layer and all sublayers. This further provides the possibility of including more entries for feature points in the CPI for the enhancement layer than the base layer, as described further below. 3 illustrates this approach in one embodiment. CPI file 302 is used for base layer file 306. The entry 304 in the CPI file 302 contains information about points in the base layer file 306. Separate CPI file 310 is used when enhancement layer 1 308a is used. Entry 312 in this CPI file 310 includes information about both the base layer 306 and Enh 1 308a. Similarly, a comprehensive CPI file exists for higher level enhancement layers.

In general, in order to decode an enhancement layer, corresponding base layer data is required because an extra pointer to the enhancement layer is not useful without a corresponding pointer to the base layer. In the embodiment shown in FIG. 3, the base layer CPI 302 may be a very small entry for one point, for example only every few seconds. This may be sufficient for random access and low quality trick play since the base layer is for use on small portable devices with generally stringent power constraints. Smaller CPIs also reduce the memory required to store CPI entries. In this case, the CPI 302 containing the offset for the base layer is retrieved and used. In the base layer + enhancement layer, more points can be used to ensure high quality trick play when playing on devices with larger screens and more power, thus having more entries (as well as more parameters per entry). Results in a CPI file. For example, if the device uses a first enhancement layer, CPI 310 is retrieved and used to provide CPI data for both the base layer and the first enhancement layer.

In the embodiment of FIG. 3, the content file corresponding to CPI 310 may alternatively be a composite encoding of base layer 306 and enhancement layer 308a. Thus, the separated content file may exist in the form of a base layer, a base layer + first enhancement layer, a base layer + first and second enhancement layer. File 306 is decoded when only the base layer is used. If the first enhancement layer is used, the complex encoded base layer file and the Enh1 file are decoded and used. Each such content file may have a separate CPI file that includes the point type, PTS, and offset for a particular base layer file or composite base layer and enhancement layer (s) file.

While the invention has been described with reference to various embodiments, it will be understood by those skilled in the art that the invention is not limited to the specific forms shown and described. Accordingly, various changes may be made in form and detail herein without departing from the spirit and scope of the invention as defined by the appended claims.

As mentioned above, the present invention is available in multilayer video encoding.

Claims (22)

A recording medium comprising a plurality of content files comprising a base layer 106 and one or more enhancement layers 108a, 108n, Further comprising a feature point information (CPI) file 102 for the base layer 106 and the one or more enhancement layers 108a, 108n, The CPI file 102 includes a series of entries 104 corresponding to the feature points 108a and 108n in the base layer 106 and the one or more enhancement layers, respectively, and the entry 104 for each feature point. A point type, a presentation time (PTS), and a separate offset for each of the base layer (106) and at least one enhancement layer (108a, 108n). delete The method of claim 1, wherein in each entry 104, an offset relative to the base layer 106 determines a memory location within the base layer 106 for the feature point of the entry 104, and each enhancement layer ( An offset to 108a, 108n, determines a memory location within each enhancement layer (108a, 108n) for the feature point of the entry (104). 4. The memory location of claim 3, wherein the memory location in the base layer 106 for the feature point of the entry 104 and the memory location in each enhancement layer 108a, 108n for the feature point of the entry 104 are determined by the entry ( Recording medium corresponding to the presentation time of 104; 4. The method of claim 3, wherein in at least a plurality of entries 104 in the CPI file 102, an offset for at least one of the base layer 106 and the enhancement layers 108a, 108n is determined by the entry 104. A recording medium, which is an absolute memory address in each layer file for a feature point. 4. The method of claim 3, wherein in at least a plurality of entries 104 in the CPI file 102, an offset for at least one of the base layer 106 and the enhancement layers 108a, 108n is known in each layer file. A measure from a starting point, the measure providing a memory address in each layer file for a feature point of the entry (104). 2. The recording medium of claim 1, wherein the CPI file (102) comprises an indication that one or more enhancement layers (108a, 108n) are deleted from the recording medium. A recording medium comprising a plurality of content files comprising a base layer 206 and one or more enhancement layers 208a, 208b, each of the base layer 206 and the one or more enhancement layers 208a, 208b. And a separate feature point information (CPI) file (202, 204, 210) corresponding to the recording medium. 9. The CPI file 202 corresponding to the base layer 206 includes a series of entries each corresponding to a feature point in the base layer 206, wherein the entry for each feature point is the base layer 206. Recording type), including the point type, the presentation time (PTS), and the offset. 10. The method of claim 9, wherein the CPI files 204, 210 corresponding to each of the one or more enhancement layers 208a, 208b include a series of entries corresponding to the feature points in each of the enhancement layers 208a, 208b, The entry for each feature point includes an offset for each enhancement layer (208a, 208b). 11. The method of claim 10, wherein each entry for a particular feature point in a CPI file corresponding to each of the one or more enhancement layers 208a, 208b corresponds to an entry for a particular feature point in a CPI file corresponding to the base layer 206. Corresponding recording medium. A recording medium having two content files comprising a base layer 306 and a first enhancement layer 308a, further comprising two feature point information (CPI) files 302,310, wherein the two CPI files 302,310 ) Includes a base layer CPI file (302) corresponding to the base layer (306) and a first CPI file (310) corresponding to the base layer (306) and the first enhancement layer (308a). 13. The base layer CPI file 302 includes a series of entries each corresponding to a feature point in the base layer 306, wherein an entry for each feature point is a point type, presentation for the base layer 306. A recording medium, including a presentation time (PTS) and an offset. 13. The method of claim 12, wherein the first CPI file 310 includes a series of entries corresponding to feature points in the base layer 306 and the first enhancement layer 308a, respectively, wherein the entry for each feature point is Recording point, presentation time (PTS), and a separate offset for each of the base layer (306) and the first enhancement layer (308a). 13. The recording medium of claim 12, wherein the recording medium comprises one or more additional enhancement layers, wherein the recording medium further comprises additional CPI files corresponding to each of the one or more additional enhancement layers, each additional enhancement layer. The CPI file for the recording medium corresponds to all enhancement layer levels (308a ...) up to the layer including the base layer (306) and the corresponding additional enhancement layer. A method for recording multilayer encoded audio / video data, Generating a CPI file 102 each comprising a series of entries 104 corresponding to feature points, each entry 104 being within the base layer 106 and one or more enhancement layers 108a, 108n. A method for recording multilayer encoded audio / video data comprising a point type, a presentation time (PTS), and one or more offsets corresponding to the feature points. A method for recording multilayer encoded audio / video data, Generating a base layer CPI file 202 that corresponds to the base layer file 206 and each includes a series of entries corresponding to the feature points, each entry having a point type, presentation corresponding to the feature points in the base layer 206. Generating a base layer CPI file, including a presentation time (PTS), and an offset; And Generating one or more additional CPI files 204, 210 corresponding to each of the one or more enhancement layer files 208a, 208b that include enhancement layer audio / video data, the enhancement layer files 208a, 208b Each corresponding additional CPI file 204, 210 includes generating one or more additional CPI files, including a series of entries that include at least an offset corresponding to a location in the corresponding enhancement layer audio / video data. How to record multilayer encoded audio / video data. 18. The multilayer encoded encoding of claim 17 wherein each entry in each additional CPI file 204, 210 for an enhancement layer file 208a, 208b corresponds to an entry in the base layer CPI file 202 for a feature point. How to record audio / video data. The method of claim 18, Accessing an entry for a feature point in the base layer CPI file (202) and using an offset in the entry to access a location corresponding to the feature point in the base layer file (206); And In order to access the location corresponding to the feature point in the corresponding enhancement layer 208a, 208b, access the corresponding entry for the feature point in the at least one additional CPI file 204, 210 for the enhancement layer 208a, 208b and Using the offset in the corresponding entry. The method of claim 17, Sequentially storing the base layer CPI file (202) and the one or more additional CPI files (204, 210) in memory; And Further comprising applying an operation based on the stored sequence to access an entry in the base layer CPI file 202 and a corresponding entry in the one or more additional CPI files 204 and 210. How to record it. A method for recording multilayer encoded audio / video data, Generating a base layer CPI file 302 that corresponds to the base layer file 306 and each includes a series of entries corresponding to the feature points, each entry having a point type, presentation corresponding to the feature points in the base layer 306. Generating a base layer CPI file, including a presentation time (PTS), and an offset; And Generating one or more additional CPI files 310 corresponding to each one or more enhancement layer files 308a that include enhancement layer audio / video data, each corresponding to enhancement layer file 308a. The additional CPI file 310 each includes a series of entries corresponding to the feature points, each entry including all enhancement layer files 308a up to the level of the file including the base layer 306 and the corresponding enhancement layer file. Generating one or more additional CPI files, comprising a point type, a PTS, and an offset corresponding to the location of the feature point within. A recording medium storing an information structure for identifying multilayer encoded audio / video data, The information structure may include a point type corresponding to a point on a clip, a presentation time corresponding to a point in the clip, and one or more corresponding points in one or more enhancement layers 108a, 108n, 208a, 208b, and 308a of the clip. A recording medium having stored thereon an information structure for identifying multilayer encoded audio / video data, including CPIs (102,204, 210,310) including offset points.

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