WO2003012790A2

WO2003012790A2 - Changing a playback speed for video presentation recorded in a field structure format

Info

Publication number: WO2003012790A2
Application number: PCT/US2002/023712
Authority: WO
Inventors: Shu Lin; Jianlei James Xie; Mark Alan Schultz
Original assignee: Thomson Licensing S.A.
Priority date: 2001-07-27
Filing date: 2002-07-25
Publication date: 2003-02-13
Also published as: MY135082A; JP2005525710A; KR20040018518A; TW579652B; CN1556993A; CN1556993B; MXPA04000745A; WO2003012790A3; BR0211447A; US7215871B2; US20030021583A1; EP1419505A2; KR100924571B1

Abstract

The invention includes a system and method for changing a playback speed of a selected video segment containing field pictures which has been recorded onto a portion of a storage medium. A selected video segment can be modified for a changed playback speed and the modified video segment can be recorded exclusively on the portion of the storage medium. A plurality of non-video packs in the selected video segment can be deleted to reduce the amount of data contained in the modified video segment. The video segment can be modified by adding at least one field picture. Alternatively, the video segment can be modified by removing at least one field picture contained in the video segment. In either arrangement, the video segment can be reencoded to produce a smoother trick mode and playback performance.

Description

CHANGING A PLAYBACK SPEED FOR VIDEO PRESENTATION RECORDED IN A

FIELD STRUCTURE FORMAT

BACKGROUND OF THE INVENTION

1. Technical Field

The inventive arrangements relate generally to methods and

apparatus providing advanced operating features for programs recorded on

disc media, for example recordable digital video discs, hard drives and

magneto optical discs.

2. Description of the Related Art

While trick modes enable a user to view recorded video at different

speeds, the video is not permanently altered by the process. If the video is

displayed at a later time, then the user must initiate another trick mode to

view the video at a different speed. Significantly, however, many users may

wish to permanently change the playback speed of a particular portion of

video by modifying the video once the video has been recorded onto a disc.

Such a process can permit speed variations during playback without the user

invoking a trick mode command. Unfortunately, several significant obstacles

exist that make editing recorded video in such a fashion impracticable.

Specifically, the space occupied by the original video is not large enough to

store the pictures that must be repeated in order to produce slow motion

playback. In addition to spatial limitations, repeating pictures on the disc can

interfere with the conventional picture structure of the video, which can

degrade the display quality of the video during playback. Modifying recorded video to produce fαst-forwαrd playback,

however, is not affected by the spatial limitations that impede slow-motion

editing. This is because fast-forward editing merely deletes pictures from the

recorded video. Nevertheless, creating fast-forward video, similar to slow-

5 motion modification, also negatively impacts the conventional picture

structure of the video. Thus, what is needed is a device that can change the

playback speed of video recorded under a field structure format yet can

overcome the spatial and structural limitations associated with such recorded

video.

l o Summary of the Invention

In a rewritable storage medium, the invention includes a method for

changing a playback speed of a selected video segment containing field

pictures which has been recorded on a portion of the storage medium. In

one arrangement, the invention includes the steps of: modifying the selected

15 video segment for a changed playback speed; and recording the modified

video segment on the portion of the storage medium. In one arrangement,

the recording step can further include the step of recording the modified

video segment exclusively on the portion of the medium. The invention can

also include the step of deleting a plurality of non-video packs in the

20 selected video segment to reduce an amount of data contained in the

modified video segment. Further, the invention can also include the step of

reducing a resolution of at least one field picture contained in the modified

video segment and lowering a bit rate of the modified video segment during

the recording step. In one arrangement of the above invention, the selected video

segment can be comprised of intra and non-intra field pictures and the

modification step can comprise the step of inserting into the selected video

segment at least one of the group consisting of dummy field picture and

repeat field pictures.

In another aspect, the number of dummy field pictures and repeat

field pictures inserted into the selected video segment is based on the

changed playback speed. Moreover, the invention can also include the

step of selectively decoding and re-encoding the modified video segment

for conventional placement of the intra and non-intra field pictures, the

dummy field pictures and the repeat field pictures.

In another arrangement, the modification can include the step of

removing at least one field picture from the selected video segment. In

addition, the number of the field pictures removed from the selected video

segment can be based on the changed playback speed.

In another arrangement, the invention includes a system for changing

a playback speed of a selected video segment containing field pictures

recorded on a rewritable storage medium. The above system includes:

storage medium circuitry for selectively reading a video segment which has

been recorded on a portion of the rewritable storage medium; a video

processor for modifying the selected video segment for a changed playback

speed; and video recording circuitry for recording the modified video

segment on the portion of the storage medium. The system also includes

suitable software and circuitry to implement the method as described above. Brief Description of the Drawings

FIG. 1 is a block diagram of a rewritable DVD device that can change

the playback speed of recorded video containing field pictures in

accordance with the inventive arrangements herein.

FIG. 2 illustrates a data structure of a rewritable DVD disc.

FIG. 3A is a flowchart that illustrates the operation of changing the

playback speed of video containing field pictures to produce slow motion

playback.

FIGS. 3B - 3H demonstrate the editing process of FIG. 3A as applied to a

conventional GOP to produce a one-half playback speed.

FIG. 4A is a flowchart that illustrates the operation of changing the

playback speed of video containing field pictures to produce fast motion

playback.

FIGS. 4B - 4F demonstrate the editing process of FIG. 4A as applied to

two conventional GOP's to produce a doubled playback speed.

Detailed Description of the Preferred Embodiments

Recordable DVD Device

A device 100 for implementing the various advanced operating

features in accordance with the inventive arrangements is shown in block

diagram form in FIG. 1. A rewritable disc medium is embodied as a

rewritable DVD in the illustrated embodiment. In many instances, as will be

noted, the rewritable disc medium can also be, for example, a hard drive or

a magneto optical disc (MOD). An example of a MOD is a mini-disc.

Moreover, the invention can also be used in a digital tape machine. In fact,

the invention is not limited to any particular storage medium device, as it can

be used in any other suitable storage medium device.

The device 100 is capable of writing onto and reading from a storage

medium, in this example, a rewritable DVD 102. Although the following

discussion primarily concerns rewritable DVD, the invention is not so limited, as

any other suitable storage medium can be used. The device can comprise a

mechanical assembly 104, a control section 120, a video/audio input

processing path 140 and a video/audio output processing path 170. The

allocation of most of the blocks to different sections or paths is self-evident,

whereas the allocation of some of the blocks is made for purposes of

convenience and is not critical to understanding the operation of the device.

The mechanical assembly 104 can include a motor 106 for spinning the

disc 102 and a pickup assembly 108 that can be adapted to be moved over

the disc 102 as the disc 102 spins. A laser on the pickup assembly 108 can

burn spots onto a spiral track on the disc 102 and can illuminate spots already burned onto the track for recording and playing back video and/or audio

program material. For purposes of understanding the invention, it is irrelevant

whether the disc 102 is recordable on one or two sides, or in the event of a

double-sided recording, whether the double-sided recording, or subsequent

reading from the disc 102, takes place from the same side of the disc 102 or

from both sides. The pickup assembly 108 and the motor 106 can be

controlled by a servo 1 10. The servo 1 10 can also receive the Playback

Signal of data read from the spiral track of the disc 102 as a first input. The

Playback Signal is also an input to an error correction circuit 130, which can

be considered part of the control section or part of the video/audio output

processing path 170.

The control section 120 can comprise a control central processing unit

(CPU) 122 and a navigation data generation circuit 126. The control CPU 122

can supply a first input signal to the navigation data generation circuit 126,

and the servo 1 10 can supply a second input signal to the navigation data

generation circuit 126. The servo 1 10 can also be considered part of the

control section 120. The navigation data generation circuit 126 can supply a

first input signal to the multiplexer (MUX) 154, which can form part of the

video/audio input processing path 140.

The output of the MUX 154 can be an input to an error correction

coding circuit 128. The output of the error correction coding circuit 128 can

be a recordable input signal supplied to the pickup 108, which can be

"burned" onto the spiral track of the disc 102 by the laser. In addition, control and data interfaces can also be provided for

permitting the CPU 122 to control the operation of the video encoder 144,

video decoder 178 and audio decoder 182. Suitable software or firmware

can be provided in memory for the conventional operations performed by

control CPU 122. Further, program routines for the editing recorded video

features 134 are provided for controlling CPU 122 in accordance with the

inventive arrangements.

A control buffer 132 for viewer activatable functions can indicate those

functions presently available, namely play, record, reverse, fast forward, slow

play, jump, pause/play and stop. In addition, an editing buffer 136 can be

provided to receive commands for implementing the recorded video editing

features.

The output processing path 170 can comprise an error correction block

130, a track buffer 172, a conditional access circuit 174 and a demultiplexer

176. The track buffer 172 can read and temporarily store for further

processing data read from the disc 102. This data can be processed by the

conditional access circuit 174, which can control propagation of the data

through the demultiplexer 176 and into respective paths for video and audio

processing. Additionally, the output processing path 170 can include a

packet video encoder 178, a TV encoder 180, an audio decoder 182 and an

audio D/A 184.

The video/audio input processing path 140 can be a signal processing

circuit for converting a conventional television signal into digitized packet data for digital recording by the device 100. The input path 140 can include

a TV decoder 142 and the packet video encoder 144. In addition, the input

processing path 140 can include an audio A/D 146 and an audio encoder

148. During normal operation, the digitized signals can be combined in a

multiplexer 150 and can then be stored in the record buffer 152 until an entire

packet has been constructed. As groups of audio and video data packets

are created, they can be combined in multiplexer 154 with appropriate

navigation packets generated in the navigation generation block 126. The

packets can then be sent to the error correction coding circuit 128. Error

correction coding circuit 128 can also be deemed to be part of the input

path 140.

If a user wishes to edit a portion of video stored on the disc 102, the

editing buffer 136 can signal the control CPU 122. In one arrangement, the

control CPU 122 can signal the packet video encoder 178 to decode the

field pictures contained in the video being read from a particular location on

the disc 102 and then to send the video containing the decoded pictures to

a packet video encoder 144. As will be explained later, in an alternative

arrangement, only a selected number of these field pictures need to be

decoded during the editing process. In either arrangement, any audio

associated with the field pictures can be forwarded to the audio decoder

182. The control CPU 122 can then instruct the audio decoder 182 to store

the audio temporarily. For purposes of creating extra space, however, the

audio is generally not recombined with the video during the editing process. Rather, the audio is typically discarded when the storage buffer in the audio

decoder 182 overflows. In addition to removing the audio component, any

subpicture information associated with the modified video can be separated

and prevented from reintegrating with the modified video.

Once the video signal containing the decoded pictures is received at

the packet video encoder 144, the video encoder 144 can modify the video

signal by adding or deleting pictures. As will be explained in detail below,

adding pictures to the video signal can create slow-motion video and

deleting pictures from the video can produce fast-forward video. The video

encoder 144 can then reencode these pictures so that the modified video

can be placed on the disc 102.

After the pictures in the edited video signal have been reencoded, the

video signal can merely propagate through the multiplexer 150 since audio is

typically not combined with the modified video signal. The edited video is

then processed in a fashion similar to that of normal video. That is, the

modified video signal is combined with navigation data in the multiplexer 154

and error corrected by error correction coding circuit 128. As will be

explained later, the edited video signal can then be recorded back onto the

disc 102 in its original space.

Notably, the present invention can be realized in hardware, software,

or a combination of hardware and software. Machine readable storage

according to the present invention can be realized in a centralized fashion in

one computer system, for example the control CPU 122, or in a distributed fashion where different elements are spread across several interconnected

computer systems. Any kind of computer system or other apparatus adapted

for carrying out the methods described herein is acceptable.

Specifically, although the present invention as described herein

contemplates the control CPU 122 of FIG. 1 , a typical combination of

hardware and software could be a general purpose computer system with a

computer program that, when being loaded and executed, controls the

computer system and a DVD recording system similar to the control section

120 of FIG. 1 such that it carries out the methods described herein. The

present invention can also be embedded in a computer program product

which comprises all the features enabling the implementation of the methods

described herein, and which when loaded in a computer system is able to

carry out these methods.

A computer program in the present context can mean any expression,

in any language, code or notation, of a set of instructions intended to cause

a system having an information processing capability to perform a particular

function either directly or after either or both of the following: (a) conversion

to another language, code or notation; and (b) reproduction in a different

material form. The invention disclosed herein can be a method embedded

in a computer program which can be implemented by a programmer using

commercially available development tools for operating systems compatible

with the control CPU 122 described above.

DVD Data Structure FIG. 2 illustrates a typical DVD arrangement. However, variations in the

structure shown are possible, and the invention is not intended to be limited

to the particular embodiment shown. As shown in FIG. 2, each DVD contains

a video manager 26 and a video title set (VTS) 28. The VTS includes video title

set information (VTSI) 27, an optional video object set for menu 29, one or

more VOBS for title 30 which contains the actual title content and a VTSI

backup 31. Each VOBS 30 is comprised of a plurality of video objects (VOB)

32. Each video object 32 includes a plurality of cells 34. Each VOBS 30 also

includes a collection of pointers to one or more cells. In this way, the VOBS 30

data links the cells 34 together and indicates in what order the programs or

cells 34 are to be played. The cells 34 within a particular VOBS 30 can be

flagged for play in any desired order. For example, they can be played

sequentially or randomly.

Each cell 34 includes a plurality of video object units (VOBU) 36. Each

of the VOBU's 36 in which the video content of the disc resides typically

contains 0.4 to 1.0 seconds of presentation material. Each VOBU starts with

exactly one navigation pack (NV_PCK) 38 and can include one or more

audio packs (A_PCK) 40, one or more video packs (V_PCK) 41 and one or

more subpicture packs (SP_PCK) 42. In addition, each VOBU 36 is nominally

comprised of one group of pictures (GOP).

Changing Playback Speed for Video Presentation Recorded in a Field

Structure Format In accordance with the inventive arrangements, a user may alter the

playback speed of video containing field pictures that has already been

recorded onto a storage medium. If the user desires to edit the recorded

video to produce slow motion video, then one or more pictures may be

inserted into the video to create such an effect. The altered video can then

be recorded onto the storage medium in the same space previously

occupied by the original video. If the user desires to create fast-forward

video, then one or more pictures may be removed from the recorded video.

Similar to the slow motion editing process, the video can be recorded in the

original video's medium space. In either process, the edited video may be

reencoded to produce higher quality playback and trick mode operation.

Many televisions employ interlaced scanning techniques. Under

interlaced scanning, the television picture is divided into two fields in which

each field represents half of the information contained in the picture. The

two fields are commonly referred to as top and bottom fields, and when

paired together, the top field and the bottom field represent an entire

picture. The top and bottom fields are temporally distinct and, in countries

with 60-Hz power line standards, are approximately 1 /60 of a second apart.

Thus, interlaced scanning permits display of 60 images to the viewer without

increasing bandwidth requirements.

The following is a conventional GOP structure in an MPEG video stream

containing field pictures in display order, which can be helpful in explaining

the inventive arrangements: BOT BOB B I T B I B bi -s B3T B₃B B₄T B₄B PST PSB BOT BOB B7T B7B PST PSB B9T B9B BI OT BI OB P I I T P U B

Bl2T Bl2B Bl3T Bl3B Pl₄T Pl4B

As shown, MPEG video containing field pictures generally uses three types of

picture storage methods: Intra (I) fields, predictive (P) fields and bidirectional

predictive (B) fields. The I, P and B fields can be either top fields - designated

by a subscript 'T" or bottom fields - designated by a subscript "B." The P fields

and B fields are commonly referred to as non-intra (non-1) fields. Experience

has shown that placing two pairs of B field pictures between each pair of I

and P field pictures works well. Accordingly, the conventional GOP structure

as shown is commonly used. Those skilled in the art will appreciate that other

GOP structures are also commonly used and may be considered

conventional. In fact, the invention can be applicable to those MPEG

encoders that are designed to encode only P fields or frames and I fields or

frames or those encoders that are limited to encoding only I fields or frames.

Referring to FIG. 3A, a flowchart 300 illustrates how slow motion editing

can be performed on video containing field pictures. FIGS. 3B through 3H

illustrate an example of this slow motion editing process. In particular, FIGS.

3B through 3H demonstrate how a single conventional GOP can be altered

to produce a one-half playback speed; however, it should be noted that the

invention is not so limited, as any portion of video may be changed to

playback at any speed slower than normal playback.

Beginning at step 310 in FIG. 3A, the device 100 can begin to read

data from the storage medium. FIG. 3B shows the form of a conventional GOP containing field pictures prior to being edited. In step 312, the

demultiplexer 176 of FIG. 1 can separate the video components of the

recorded video signal from the non-video components and can discard the

non-video components. Examples of non-video components include

A_PCK's 40 and SP_PC 's 42. The NV_PCK's 38, however, can be left in the

video signal being edited since, in accordance with DVD standards, each

VOBU 36 is required to have an NV_PCK 38. The non-video components can

then be discarded.

As shown in step 314 and in accordance with the inventive

arrangements, only a selected number of field pictures need to be decoded.

In one arrangement, one or more I field pictures in the video signal can be

decoded. This will enable such field pictures to be re-encoded into non-1

field pictures for purposes of saving space, a process that will be explained

more fully below. In addition, since adding pictures to the video signal to

produce a slower playback will create the need for additional GOP's, one or

more non-1 field pictures can be decoded thereby enabling such pictures to

be re-encoded into I field pictures. This procedure ensures that each

additional GOP will have at least one I field picture from which to create the

remaining non-1 field pictures.

At step 316, the field pictures that were selectively decoded in step 314

can now be re-encoded. As an example, the I field pictures that were

decoded in step 314 can be re-encoded into P field pictures. An example of

this process is shown in FIG. 3C, as field picture I₂B is decoded and re- encoded into field picture P2B. Re-encoding I field pictures into P field

pictures helps reduce the amount of information needed to be stored on the

medium since a P field picture typically requires less storage space than an I

field picture. It should be noted, however, that the invention is not so limited,

as the I field pictures can be re-encoded into any other suitable format.

Continuing with step 316, the non-1 field pictures that were decoded in

step 314 can be re-encoded into I field pictures. This ensures that any

additional GOP's will have the necessary reference field picture to construct

the remaining non-1 field pictures. FIG. 3D shows an example of this process,

as field picture PST is re-encoded into field picture 1ST. It should be noted,

however, that FIG. 3D is merely an example, as any other suitable non-1 field

picture can be selected for decoding and subsequent re-encoding to

produce the reference field picture.

Moving to step 318 in FIG. 3A, if dummy field pictures are to be added

to the video being edited, then the packet video encoder 144 can insert one

or more such pictures into the video signal, as shown at step 320. A dummy

field picture is an MPEG picture which is merely a repeat of a particular I field

picture or a non-1 field picture. Notably, however, the discrete cosine

transform (DCT) coefficients and the motion vectors of the dummy field

picture are set to zero. Thus, dummy field pictures require very little storage

space on the medium. Further, dummy field pictures are already in a

compressed format and, therefore, do not have to be encoded prior to

being recorded onto the storage medium. In one arrangement, dummy field pictures can be placed either

immediately before or after their parent field picture; however, the invention

is not so limited, as the dummy field pictures can be inserted anywhere in the

video signal. The number of dummy field pictures inserted into the video

signal depends on the selected slow motion speed. For example, a single

dummy field picture can be inserted either before or after each parent field

picture in the video signal, including each I field picture that has been re¬

encoded into an non-1 field picture, to produce a playback speed that is

one-half of normal playback speed. FIG. 3E illustrates this example. A slower

playback speed requires the insertion of a greater number of dummy field

pictures.

Although these dummy field pictures can be inserted anywhere in the

video being edited, in one arrangement, the dummy field pictures can be

strategically inserted to produce a smoother playback. That is, the top field

and bottom field pictures can be grouped so that the parent top field

pictures and their associated dummy field pictures are sequentially placed.

For example, if the desired playback was one-third that of normal playback,

then two dummy top field pictures can be inserted either before or after the

top field picture being replicated. Alternatively, the original top field picture

can be placed between the dummy top field pictures. This process can also

be duplicated for the bottom field pictures. FIG. 3F shows an example of this

procedure. Inserting the dummy field pictures in this manner can enable a particular field picture and its associated dummy field pictures to be

displayed in a successive order.

As shown in FIG. 3F, during playback, the top field Pπ and its two

dummy field pictures Pπdi, Pιτd2 can be displayed in succession. Likewise,

bottom field PI B and its associated dummy field pictures PiBdi, PiBd2 can be

consecutively displayed as well. Since each top field picture is temporally

similar to the other top field pictures and each bottom field picture is

temporally similar to the other bottom field pictures, placing top field pictures

and bottom field pictures in groups for successive display produces a

smoother playback. Positioning top and bottom field pictures in an alternate

fashion so that the top and bottom field pictures would be alternately

displayed would produce a choppier playback.

The invention is not limited to adding dummy field pictures to the video

being edited to create slow motion playback. As shown in step 422 in FIG.

4A, an alternative arrangement exists in which one or more repeat field

pictures can be inserted into the video signal for purposes of slow motion

editing. A repeat field picture is an uncompressed picture that is a duplicate

of its parent field picture.

If repeat field pictures are to be added, then one or more such

pictures can be inserted into the video being edited at step 324. Similar to

the process of inserting dummy field pictures, the number of repeat field

pictures added to the video can be determined by the desired playback

speed, i.e., a slower playback speed requires a greater number of field pictures to be added. Similar to the insertion of dummy field pictures, the

repeat field pictures can be inserted immediately before or after their parent

field pictures. Further, it is also preferable to group top field repeat pictures

together as well as bottom field repeat pictures together for purposes of

smoother playback; however, it should be noted that the invention is not so

limited as the repeat field pictures can be inserted anywhere in the video

being edited.

FIG. 3E, in addition to illustrating the insertion of dummy field pictures for

a one-half speed playback, also represents the result of adding repeat field

pictures to produce a one-half speed playback. Once the repeat field

pictures are inserted, these pictures can be encoded, as shown at step 326 in

FIG. 3A. Thus, in accordance with the inventive arrangements, one or more

dummy field pictures, one or more repeat field pictures or a combination

thereof can be inserted into the video being edited to produce slow motion

playback.

After the dummy and/or repeat field pictures are placed in the video

signal as shown in FIG. 3E (and the repeat field pictures are encoded), the

GOP can be divided into two or more new GOP's illustrated in FIG. 3G and

shown in step 328 in FIG. 3A. It is desirable to separate the video signal into

two or more new GOP's because the number of field pictures in the portion of

video being edited has increased, and DVD standards limit the number of

field pictures that a GOP can contain to thirty-six. Although up to thirty-six

fields can be placed in either the original GOP or the newly created GOP's, an equal number of field pictures is preferably placed in each GOP thereby

enabling each GOP to undergo further processing, if desired, in order to

conform to the conventional GOP structure.

The new GOP's can now be recorded onto the storage medium, as

shown in step 330. In accordance with the inventive arrangements, the

edited video can be placed in the same space that the original video

previously occupied. This is because any dummy field pictures that have

been placed in the video require very little storage space since they do not

contain any encoded image information. Further, encoded repeat field

pictures typically contain only slight amounts of encoded information since

they are typically substantially identical to their parent field pictures.

Moreover, whatever storage space is required to fit these pictures into the

original space can be accommodated using the space on the storage

medium that was previously used to store the deleted non-video information.

In one arrangement, however, if there is not enough room on the

storage medium to fit the edited video in the original recording location, then

a certain number of field pictures can be decoded and then re-encoded to

reduce their picture resolution or quality. Such a process reduces the amount

of storage space required for the field pictures. In an alternative

arrangement, the bit rate of the video signal can be lowered as the edited

video is being recorded onto the storage medium. Although lowering the bit

rate can result in the loss of some of the video data and a corresponding

reduction in picture resolution, such a process can reduce the amount of physical space required on the media to record the modified video

sequence and therefore permit the edited video signal to fit in the original

recording location.

In an alternative embodiment, once the dummy and/or repeat field

pictures have been added, one or more of the GOP's containing the edited

video can be re-encoded to match the conventional GOP structure as

shown in FIG. 3B. Re-encoding the new GOP's into a conventional GOP

structure can produce a smoother playback and improve trick mode

performance. To do so, a number of the field pictures in the GOP's can be

decoded and then subsequently re-encoded into the conventional GOP

format. As an example, referring to FIGS. 3G and 3H, Boτ and Bodτ of GOPi do

not have to be decoded and then re-encoded since a conventional GOP

containing field pictures typically begins with four B field pictures. Continuing

with the example, BIT, however, can be decoded and re-encoded into field

picture lιτ. This field picture, In, can now serve as the reference field picture

for GOPi . This process can continue until the structure of GOPi and GOP₂

matches a conventional structure, as shown in FIG. 4H. It should be noted,

however, that the foregoing discussion is merely an example, as any other

suitable sequence can be used to re-encode one or more of the GOP's in the

edited video into conventional GOP's.

In an alternative arrangement, if the GOP's are to be re-encoded to

match a conventional GOP structure, then all the field pictures in the video

being edited can be decoded at step 314, rather than decoding only a select number of field pictures as previously discussed. This particular

arrangement, however, does not alter the other steps in flowchart 300.

Referring to FIG. 4A, flowchart 400 illustrates two ways how fast motion

editing can be performed on video containing field pictures. FIGS. 4B

through 4F illustrate an example of each of these fast motion editing

processes as applied to two GOP's to create a double speed playback;

however, it should be noted that the invention is not so limited, as any portion

of video may be changed to playback at any speed faster than normal

playback. In step 410, the device 100 can begin to read data from the

storage medium. In step 412, the demultiplexer 176 of FIG. 1 can separate

the video component of the recorded video signal from the non-video

components, such as A_PCK's 40 and SP_PCK's 42. The non-video

components can then be discarded. Similar to the slow motion process of

FIG. 3A, the NV_PCK's 38 can be left in the video signal being edited. FIG. 4B

shows the form of two conventional GOP's containing field pictures as they

are presented to the packet video encoder 144.

As shown in step 414, if the edited video will not undergo a reencoding

step to conform each edited GOP to a conventional GOP structure, then the

device 100 can begin to remove B field pictures from the video signal. This

process is shown at step 416 in FIG. 4A and in FIG. 4C. Referring to FIG. 4C,

the B field pictures removed can be distributed throughout the GOP rather

than in lengthy groups containing successive B field pictures. Removing B

field pictures in this fashion is preferable because it will produce a smoother playback and trick mode performance. As an example, in FIG. 4C, field

pictures Boτ and BOB can be removed and then field picture B_{I T} can be

retained before field pictures BI B, B₃τ and B_3B are deleted. Subsequently, field

picture B₄τ can be retained and the deletion process can continue. It should

be noted, however, that the example shown in FIG. 4C is not intended to limit

the invention to this particular deletion sequence, as any other suitable

deletion sequence may be used.

The overall number of field pictures deleted from the video signal can

depend on the selected fast motion speed. For example, to produce a

playback speed twice as fast as normal playback, one-half of the field

pictures contained in each GOP can be deleted from the video signal. This is

the result achieved in FIG. 4C. At step 418 in FIG. 4A, the device 100 can

determine whether removal of the B field pictures was sufficient for purposes

of producing the desired fast-forward playback speed. If not, then the

device 100 can begin to remove P field pictures from the video, as shown in

step 420. As in the case of B field picture removal, the P field pictures that are

deleted are preferably distributed throughout the GOP.

Once the proper number of field pictures have been deleted, the

remaining pictures from the edited GOP's can be consolidated to fill one or

more of the GOP's contained in the edited video signal, in accordance with

step 422 and as illustrated in FIG. 4C. These field pictures can then be

recorded onto the storage medium, as shown in step 424 in FIG. 4A. In

contrast to the slow motion editing process, the fast-forward edited video can easily fit in its original medium space since one or more pictures have

been deleted from the video.

In one arrangement, dummy data be recorded over the remaining

storage medium space, as shown in step 426. This process can prevent the

recorder from displaying parts of the original video which still remain on that

portion of the storage medium not receiving the edited video. As an

example, the stream ID's present in the V_PC 's 41 of the original video

located in the remaining space can be modified to instruct the device 100

that this video should be ignored. Once the stream ID's are modified, the

video, now considered dummy data, can then be recorded back onto the

storage medium in its original location. It should be noted, however, that the

invention is not limited to this particular example, as other well known

techniques can be used to cause the device 100 to ignore any remaining

original video in the original medium space left over by the editing process.

Turning back to step 414, if the edited GOP's are to be reencoded to

match the structure of a conventional GOP, then the field pictures in the

video can be decoded in accordance with step 415. At step 417, field

pictures can be removed from the video signal being edited. Since the

GOP's containing these pictures will be re-encoded to match a conventional

GOP - an example of which is shown in FIG. 4D - it is irrelevant as to which

field pictures are deleted from the video signal; however, similar to the

previously discussed fast-forward editing process, the field pictures that are

discarded are preferably distributed throughout the GOP for purposes of creating a smoother playback. The number of field pictures that are deleted

can be based on the desired fast-forward playback speed. FIG. 4E illustrates

this process as applied to the two GOP's of FIG. 4D to produce a doubled

playback speed. It should be noted, however, that the example shown in

FIG. 4E is not intended to limit the invention to this particular deletion

sequence, as any other suitable deletion sequence may be used to create

the desired playback speed.

At step 419 of FIG. 4A, the remaining field pictures can be

consolidated, and these pictures can then be re-encoded to match the

structure of a conventional GOP containing field pictures, in accordance

with step 421 of FIG. 4A and shown in FIG. 4F. It should be noted, however,

that the example shown in FIG. 4F is not intended to limit the invention to this

particular re-encoding sequence, as any other suitable re-encoding

sequence may be used. At step 423, once the field pictures have been re-

encoded, the field pictures can be recorded onto the storage medium in the

medium space previously occupied by the original video. In addition,

dummy data can then be inserted into any remaining storage medium

space, as previously described relative to step 426.

Claims

Claims:

1 . In a rewritable storage medium, a method for changing a playback

speed of a selected video segment containing field pictures which has been

recorded on a portion of said storage medium comprising the steps of:

modifying said selected video segment for a changed playback

speed; and

recording said modified video segment on said portion of said

medium.

2. The method according to claim 1 , wherein said recording step further

comprises the step of recording said modified video segment exclusively on

said portion of said medium.

3. The method according to claim 1 , further comprising the step of

deleting a plurality of non-video packs in said selected video segment to

reduce an amount of data contained in said modified video segment.

4. The method according to claim 1 , further comprising the step of

reducing a resolution of at least one field picture contained in said modified

video segment.

5. The method according to claim 1 , further comprising the step of

lowering a bit rate of said modified video segment during said recording

step.

6. The method according to claim 1 , wherein said selected video

segment is comprised of intra and non-intra field pictures.

7. The method according to claim 6, wherein said modification step

comprises the step of inserting into said selected video segment at least one

of the group consisting of dummy field pictures and repeat field pictures.

8. The method according to claim 7, wherein the number of said dummy

field pictures and said repeat field pictures inserted into said selected video

segment is based on said changed playback speed.

9. The method according to claim 8, further comprising the step of

selectively decoding and re-encoding said modified video segment for

conventional placement of said intra and non-intra field pictures, said

dummy field pictures and said repeat field pictures.

10. The method according to claim 1 , wherein said modification comprises

the step of removing at least one field picture from said selected video

segment.

1 1 . The method according to claim 10, wherein the number of said field

pictures removed from said selected video segment is based on said

changed playback speed.

12. A system for changing a playback speed of a selected video segment

containing field pictures recorded on a rewritable storage medium,

comprising:

storage medium reading circuitry for selectively reading a video

segment which has been recorded on a portion of said rewritable storage

medium;

a video processor for modifying said selected video segment for a

changed playback speed and for providing a modified video segment; and

video recorder circuitry for recording said modified video segment on

said portion of said storage medium.

] 3. The system according to claim 12, wherein said video recording

circuitry records said modified video segment exclusively on said portion of

said storage medium.

14. The system according to claim 12, wherein said video processor

deletes a plurality of non-video packs in said selected video segment to

reduce an amount of data contained in said modified video segment.

15. The system according to claim 12, wherein said video processor

reduces a resolution of at least one frame contained in said modified video

segment.

16. The system according to claim 12, wherein said video processor lowers

a bit rate during recording of said modified video segment.

17. The system according to claim 12, wherein said video segment is

comprised of intra and non-intra field pictures.

18. The system according to claim 17, wherein said video processor inserts

into said selected video segment at least one of the group consisting of

dummy field pictures and repeat field pictures.

19. The system according to claim 18, wherein the number of said dummy

field pictures and said repeat field pictures inserted into said selected video

segment is based on said changed playback speed.

20. The system according to claim 19, wherein said video processor

selectively decodes and re-encodes said modified video segment for

conventional placement of said intra and non-intra field pictures, said

dummy field pictures and said repeat field pictures.

21 . The system according to claim 12, wherein said video processor

removes at least one field picture from said selected video segment.

22. The system according to claim 21 , wherein the number of said field

pictures removed from said selected video segment is based on said

changed playback speed.