WO2008078223A1

WO2008078223A1 - Frame accurate conditional access on blu-ray disc mpeg 2 transport streams

Info

Publication number: WO2008078223A1
Application number: PCT/IB2007/055068
Authority: WO
Inventors: Kousik S. Ramasubramaniam
Original assignee: Koninklijke Philips Electronics, N.V.; U.S. Philips Corporation
Priority date: 2006-12-20
Filing date: 2007-12-12
Publication date: 2008-07-03
Also published as: TW200842836A

Abstract

A user application is provided on a recorder/player for controlling access to video on a frame-by-frame basis. Initially, the playlist is indicates frame portions that are all unhidden, the user marks frame portions for conditional access by inserting specific markers. The user enters a password to enable conditional access for the marked frame portions. Upon playback, the system will require entry of the password to enable viewing of the marked frames.

Description

FRAME ACCURATE CONDITIONAL ACCESS ON BLU-RAY DISC MPEG 2

TRANSPORT STREAMS

The invention pertains to editing of audio-visual data streams, and more particularly, to frame accurate Conditional Access of audio-visual streams.

The state of the art high capacity storage standard is Blu-ray. Blu-ray is a format that offers dramatically greater storage capacities than legacy optical storage media. There exist numerous applications that Blu-Ray Discs (BD) can be used for including but not limited to mass storage, storage of digital audio- visual (AfV), streams from any of numerous sources including but not limited to camcorders, digital video recorders, optical storage media, satellite transmissions, broadcast transmissions etc. The very high storage capacities and high-speed data transfer rates of BD can provide high- definition video recording that was not possible prior advent of Blu-ray.

Digital video recorders typically record video in one of the Motion Picture Expert Group (MPEG) formats. These formats offer very little or no access restrictions. Advanced features (such frame accurate conditional access) as currently known within the art are typically computational and/or memory intensive making these advanced features unrealistic to include within consumer products. The currently available techniques decode the video within the MPEG streams and then re-encode them again for storing in the same MPEG format. These techniques provide for basic conditional access, however, they are not sufficient for professional or high-end consumer electronics products. Current consumer electronics products, implement conditional access for digital video recordings that is either highly proprietary and therefore not portable, or so limited that frame accurate conditional access is not provided. Therefore, currently available techniques must compromise between uniformity versus completeness.

One of the more common currently available techniques for editing video sequences require that editing take places using the boundaries that are associated with the Group of pictures (GOP). By selecting a frame or set of frames to be edited, all frames within that GOP must be edited. Therefore, using this approach, frames not intended to be subjected to conditional access, will be subjected to conditional access or vice versa because the GOP boundary is used to determine which frames are edited. This approach is referred to as GOP accurate editing and is quite suitable for low end products, but editing at GOP level is not acceptable for high end professional products. Fig. 1 illustrates editing that occurs at the GOP level, where a video sequence having N GOPs having a first GOP 12, a second GOP 13, a N- 1^st GOP 14 and a Nth GOP 15. Using GOP accurate editing, the system will shift the editing boundaries to coincide with the GOP boundaries. For example, in order to edit video sequence 11 in which point A indicates the starting frame of a sequence of frames to be edited is inside the boundaries of GOP 12. GOP 12 has a starting point Ia and proceeds until the starting point of next GOP 13 at point a2. Video sequence 11 that is desired to be edited has ending point B, which must be either shifted to point b 1 (the end of the previous GOP 14) or to point b2 (the end of the current GOP 15). This situation becomes worse the more frames that the encoder has within a GOP. Frame- accurate editing is more precise than GOP based editing and does not result in the shifting of points A and/or B as shown in Fig. 1. Conventional techniques for frame-accurate editing are achieved by re-encoding the edited GOPs. Unfortunately, MPEG re-encoding is time-consuming, computationally intensive process requiring substantial hardware resources to perform the re-encoding. Therefore, there remains a need in the art for frame accurately editing an MPEG stream.

The prior art has presented a solution to the problem of resource demand for re-encoding a MPEG stream to provide frame accurate seamless playback at edit points in an MPEG stream by employing a bridge sequence that is generated and stored between the edit points. Re-encoding of MPEG frames to create a bridge sequence generally takes about 2 to 4 times more computing power than that of real-time decoding of MPEG frames.

One idea to solve the problem of demanding resources has been presented in WO2006054244 (the contents of which are hereby incorporated by reference) for re- encoding a MPEG stream is to provide frame accurate seamless playback at edit points in an MPEG stream. There is no teaching within WO2006054244 for any conditional frame accurate play back. In view of the foregoing, there remains a need within the art for frame accurate editing without the need of generating a bridge sequence.

Therefore, it is an object of the invention is to provide frame accurate editing without the need of generating a bridge sequence.

The advent of digital broadcasting, availability of more computing power, increased memory in consumer products and storage technology offering higher bit rates, like Blu-ray, create the potential of offering advanced conditional access features that are realizable within consumer products.

The Blu-ray specification is robust enough to enable techniques for frame accurate conditional access. The BD-RE (Blu-ray Disc Rewritable) specification defines real and virtual play lists which can identify specific video sequences within MPEG-2 transport streams. The BD-RE specification further defines a Blu-ray Disc Personal Identification Number (PIN) that provides locking features that can be used by for playback or recording.

It is an object to provide an embodiment to provide a method and apparatus for implementation of frame conditional access using existing standards. It is a further object to provide an embodiment to provide a method and apparatus for the implementation of frame conditional access using the he Disc PIN and password as defined by the rewritable Blu-ray standard specifications (BD-RE).

It is a further object to provide an embodiment to mitigate, alleviate or eliminate one or more of the above-identified deficiencies in the art and disadvantages singly or in any combination and solves at least the above mentioned problems by providing, a method, an apparatus, a corresponding decoder, and a computer-readable medium comprising program code, for frame accurate editing.

It is a further object to provide an embodiment to use marks defined in a standard for defining edit-in and edit-out points in an audio-visual (A/V) stream for the implementation of frame conditional access. It is a further object to provide an embodiment for a method for frame accurate conditional access for an encoded audiovisual (AV) stream, wherein the method includes employing a mark used for identifying a sequence from the AV stream that allows the sequence to be viewed only if a PIN is correctly entered. It is further an object to provide an embodiment for an apparatus that can frame accurate edit an encoded A/V stream, wherein the apparatus is configured for setting a mark indicating a start and duration of a sequence of frames to be skipped within the AV stream during playing of the edited AV stream.

It is a further object to provide an embodiment to provide a computer- readable medium for providing frame accurate Conditional Access for an encoded A/V stream, for processing by a computer, and comprises a code segment for setting a mark indicating a start and duration of a sequence of frames to be skipped during playing the AV stream unless a PIN is correctly entered.

It is a further object to provide an embodiment for a decoder system that can decode an encoded AV stream from a storage medium. The decoder system including a decoder for decoding the encoded AV stream is configured to decode the AV stream faster than nominal speed when skipping a section which has been designated during editing as not allowed to be played without input of a PIN.

It is a further object to provide an embodiment with a frame buffer configured for storing decoded frames from the decoder and feeding an output for decoded frames at nominal speed, wherein the decoder is configured to stop feeding the buffer and to continue reading from the encoded stream at the beginning of a last GOP, or a first GOP depending on the playback direction whenever a PIN is correctly entered.

It is a further object to provide an embodiment with a video sequence indicated by a skip-start mark that is not played when the skip-start mark is reached, and to continue playing the video sequence after the last frame indicated by a duration period that is also marked in the video sequence to provide for seamless playback that does not play the video sequence unless a PIN is entered.

It is a further object to provide an embodiment with a fast user response that does not require re-encoding of MPEG frames.

It is a further an object to provide an embodiment that accurately frame edits an encoded audiovisual (AV) stream that does not require extra free storage medium space.

It is a further an object to provide an embodiment that accurately frame edits an encoded audiovisual (AV) stream that does not require a bridge sequence to be created.

These and other aspects, features and advantages of which the invention is capable of will be apparent and elucidated from the following description of embodiments of the present invention, reference being made to the accompanying drawings, in which

Fig. 1 is a schematic illustration of GOP-accurate editing of a MPEG-2 stream;

Fig. 2 is a schematic illustration of an example of a skip- start mark;

Fig. 3 is a schematic illustration of a decoder model; Fig. 4 is a flow chart illustration of a method according to an embodiment;

Fig. 5 is a schematic illustration of an apparatus according an embodiment;

Fig. 6 is an illustration of a real play list and a virtual play list according to an embodiment.

The following description focuses on embodiments that are applicable for frame accurate editing that can be used with standards to provide frame accurate marking of video streams. Variations of the embodiments discussed herein will be readily apparent to those skilled in the art. These variations should be viewed as being inclusive of other A/V storage formats including, for example HD-DVD, by employing features within these alternate storage formats that can provide the equivalent functions to the markers, PIN (password) and flags similar to those described herein for BD-RE. The embodiments described herein use marks available within standards for defining the recording format of the storage medium. The present invention may be implemented with any storage media, e.g. an optical disc, a HDD, a media card, etc.

A mark can be generally defined as a pointer referenced by a time stamp on the global time axis of an AV stream represented by a title. A mark can be used to reference highlights or characteristic scenes for playback. Furthermore, a mark may have several attributes like a name and duration. The duration defines the length of the mark e.g. the length of a chapter mark. An application format defines the usage of several marks. One application usage of a mark is to hide the AV part identified by the length of the mark from playback. In the Blu-ray Disc specification version 1.0 this kind of mark is called a skip-start mark and is used to provide frame accurate conditional access as will be described in more detail below.

An example of a skip-start mark is given in Fig. 2. An AV stream 20 is illustrated, wherein a skip- start mark defines the start 21 of a sequence 22 of frames of the AV stream to be skipped. As mentioned above, the skip-start mark comprises information about the time (t in Fig. 2) duration lover which the AV stream shall be skipped during playback, i.e. the playback of the AV stream ends at the end of the frame 23 before the skip-start mark and is continued with the first frame 24 after the end of the time duration indicated by the mark.

One embodiment of the Blu-ray standard defines skip- start marks in section 4.3.7.3 of the BD-RE (Blu-Ray Disc Recordable) specification version l\0 along with a specifiable duration. This BD-RE specification is for instance available from Philips Intellectual Property and Systems (IP&S) at http://www.licensing.philips.com/. These BD-RE skip- start marks may be inserted at a frame accurate level. As already mentioned, the skip- start marks are an indication to a player of the recorded BD comprising such marks to skip the specified portion of the A/V stream and are usually used to hide selected scenes for playback.

It should be noted that the skip-start mark is specifically defined for playback and there is no suggestion or motivation provided by the BD-RE specification vl.O, to use the defined playback skip marks for edit-in/out points.

Frame accurate Conditional Access on MPEG streams using features standard to the BD-RE specification is provided by performing GOP accurate editing on the video stream and then to using skip- start marks together with a marker defined data, which are specified in section 4.3.8 and section 4.3.7.3 of the above-mentioned BD-RE specification. Skip periods is defined in Fig. 1 by placing a skip-start mark at point A having a duration from point A to a2 and another skip-start mark is put at point bl having a duration from point bl to B. The frames that belong to the skipped time period are the frames for which Conditional Access is desired and referred to herein as skip frames. These skip frames can be invisibly decoded in background mode to transparently realize frame accurate steps forward and/or backward during playback.

Another embodiment is described with reference to Fig. 4, having the following steps: 40 load AV stream from BD to editing device, 41 edit AV stream on a GOP level, 42 edit AV stream on frame level, and 43 write start-stop markers on BD. In step 40 an AV stream is read from a BD to a suitable editing apparatus. The AV stream is edited on a GOP level in step 41, which has a computational advantage. The user selects a region of the AV stream having a sequence of frames (referred to herein as segments) for which conditional access is desired. When the segment is identified on a GOP level, the editing is in step 42 continued on frame level, i.e. the user identifies exactly the first frame and the last frame of the segment for which conditional access is to be applied. The segments for which conditional access is desired could be content that is deemed violent or sexual in nature as an example. The user can set an edit- in point at the first frame and an edit-out point at said last frame for which conditional access is desired using various means such as, for example, a graphical user interface and input devices such as a mouse, a touch screen, a remote control etc. According to the method, a skip- start mark is set at the first frame and the duration is set to have a length from the first frame to the last frame of the segment for which conditional access is desired. In step 43 this mark is recorded to the BD, which results in the desired segment to be skipped during playback unless the condition required for access is supplied.

According to an embodiment, skip- start-marks as defined with the BD-RE are used for establishing conditional access. The skip- start- marks indicate the beginning of those portions of a video sequence for which conditional access is desired. These marks are used to implement edit-in and edit-out points to aid frame accurate seamless playback, without the need to generate a bridge sequence.

An application of using the BD skip- start- marks for frame accurate editing is shown in Fig. 5 wherein Blu-ray recorder 50 provides the user feeling "What You Edit Is What You Get", meaning that frame accurate editing is performed by stepping forward and backward through a recorded video, frame-by-frame. The user locates a desired scene for which conditional access is to be applied, as described above. While playing the edited video, the scenes for which conditional access is applied will not be displayed within the condition being satisfied. The condition could be entry of a password or PIN number. The viewer could be prompted for entry of a pas-word or PIN number as a condition to gain access to the content in order to view the content for which conditional access has been applied. The conditional access is applied at a frame accurate level. Alternatively, the condition can be applied without the viewer being prompted.

In a scene mode, selected areas will be played, while unselected will be skipped. This operation mode is for instance used when the user wants to extract material from a video sequence. In this case, the start-skip marks are set suitably at the beginning of the unselected areas and the duration is set to the length of the unselected area, respectively.

The above-described technique is performed in conformance with the BD- RE standard. As maker data provided for in the BD specifications is used, the method is compatible with all other implementations of the BD specifications. It will be understood by those skilled in the art that similar techniques can be performed in other standards that provide for indicia that allow the marking of frames within audio-visual streams. Referring to Fig. 6, an embodiment envisions a sequence of actions.

Initially, a real play list is created which has portions A, B, C and D which are all initially unhidden. In the example shown in Fig. 6, the user marks portion C for conditional access (i.e. lock/hide portion C). Marking video portions can be done in a frame accurate way by inserting specific markers defined in the BD-RE standard. The system asks for password during playback.

Embodiments can be modeled based on the BD-RE standard. For example, the BR-RE standard currently defines five directories, each of the five directories is provided with the potential for a unique password. If a directory is to be unprotected, then the BDAV_protect_flag (as defined in Sec 4.2.2.2 of the BD-RE standard part 3 - Audio Visual Basic Specifications) is set to a logical 0. The BR-RE standard also defines a playback_protect_flag for individual pieces of content within any given directory. An entire directory can be left unprotected by setting the BDAV_protect_flag to a logical 0. If an entire directory is left unprotected, then individual content items can still protected by setting playback_protect_flag to a logical 1. During the editing process, in order to provide conditional access for specific content items, the BDAV_protect_flag is set to a logical 0 and the playback_protect_flag for that piece of content is set to a logical 1. At this point the system will request the user to input a password. The user can enter a 4 digit password (with system reconfirmation) which is stored as the Disc PIN field (defined in Sec 4.2.2.2 of the BD-RE standard part 3 - Audio Visual Basic Specifications). Each time the playback of a playlist (real or virtual) with such hidden portions is initiated, the system can ask for the password. If the correct password is entered, the hidden portions will also be played. If the correct password is not entered, then only the non-hidden portions of the playlist will be played. The password is stored as the Disc PIN field (as defined in Sec 4.2.2.2 of the BD-RE standard part 3 - Audio Visual Basic Specifications).

An embodiment for a decoder used for accessing frame accurate conditional access a buffer memory between the decoder and the output is illustrated in Fig. 3. An encoded AV stream 30 is read from e.g. a BD into a decoder 31. Buffer 33 is a first-in first-out type (FIFO) of storage device used to retain the decoded frames 34. The decoded frames 32 from the AV stream are put in the frame buffer 33 in a FIFO manner during playback of the AV stream. As long as buffer 33 does not encounter frames with a mark for conditional access, the decoder will typically be filled with the frames 34. A suitable size for buffer 33 could be the predefined maximum number of frames that a skip- start mark can indicate to skip. If the decoder 31 reaches the start 21 of a skip- start mark, it starts reading at the beginning of the last GOP in the hidden area, i.e. the area 22 as illustrated in Fig. 2 indicated by the skip-start mark. For instance in the example of Fig. 1, this is GOP 15. The decoder starts decoding the frames from this GOP in background mode and not placing them into the frame buffer 33. The output 35 of the decoder model keeps outputting frames from the frame buffer 33 to guarantee seamless playback. Once decoder 31 decodes the last frame in the hidden area 22 of the skip-start mark, all the succeeding frames are then again placed into the frame buffer to insure seamless playback.

Although, the decoder 31 described a FIFO for buffer 33 it will be understood by those skilled in the art that numerous types of storage devices can be used for buffer 33. Alternatively, no separate storage device is required and decoded frames could be placed in mass storage.

Embodiments envision employing standard-defined entities. The embodiments combine certain entities defined in the standard in a particular way to achieve the password protection. For example, a recorded any home video, (for eg. wife giving birth to our child, vacationing with wife etc) may contain subject matter for which it is desirable to require a PIN or password to allow viewing of when one would definitely want to password protect specific segments when viewing it with our entire family. If a recorded sequence contains a movie broadcast from the pay channel onto a BD-RE (copy-once or copy free movies), a password may be required for specific segments. There are numerous uses for requiring a password for viewing particular sequences.

Still other embodiments can employ DVD+RW standardizations. The

DVD+RW standard has chapter hiding which is intended to block specific segments of video from being played back by a normal play key. This chapter hiding does not completely block the end-user from playing back the hidden sections. The user only needs to invoke editing or click "play full title" in the edit menu. The chapter-hiding concept was introduced in DVD+RW as a compromise to achieve full compatibility with the DVD-Video standard (since one of the major strong points of DVD+RW is its high compatibility with D VD- video players. From a standardization perspective, the BD-RE standard (per se) does not require DVD-video compatibility. Still a BD- RE recorder can playback DVD video discs, and true blocking of specific video segments can be done on DVD video discs using a BD-RE recorder that employs the above discussed embodiments.

Applications and use of the above described embodiments are various and include exemplary fields such as the complete range of Blu-ray recording and playback products, such as consumer or professional BD recorders, BD storage solutions, etc.

Further embodiments include any A/V storage applications that make use of a mark as explained above.

Further embodiments provide that the video payload is not edited at all. Only additional metadata of the video, i.e. skip-start mark positions and the maker defined data is additionally written to the disc. Embodiments can be implemented in any suitable form including hardware, software, firmware or any combination of these. Other embodiments are envisioned that can be implemented as computer software running on one or more data processors and/or digital signal processors. The elements and components of an embodiment may be physically, functionally and logically implemented in any suitable way. Indeed, the functionality may be implemented in a single unit, in a plurality of units or as part of other functional units. As such, the invention may be implemented in a single unit, or may be physically and functionally distributed between different units and processors.

Although embodiments have been described above, these embodiments invention should not limit the scope of the invention. Rather, the accompanying claims should determine the scope of the invention. It should be understood that different marks than those described above. Furthermore, a person skilled in the art will understand that the above embodiment is based on forward play of the edited video stream and that, when reversing the playback direction of the edited video stream, the same principles apply as laid down above, only in a different direction.

In the claims, the term "comprises/comprising" does not exclude the presence of other elements or steps. Furthermore, although individually listed, a plurality of means, elements or method steps may be implemented by e.g. a single unit or processor. Additionally, although individual features may be included in different claims, these may possibly advantageously be combined, and the inclusion in different claims does not imply that a combination of features is not feasible and/or advantageous. In addition, singular references do not exclude a plurality. The terms "a", "an", "first", "second" etc do not preclude a plurality. Reference signs in the claims are provided merely as a clarifying example and shall not be construed as limiting the scope of the claims in any way.

Other embodiments can use the features described by the above discussed embodiments for a scene mode wherein selected areas will be played, while unselected will be skipped. Here, the start-skip marks are set suitably at the beginning of the unselected areas and the duration is set to the length of the unselected area, respectively. Each of these modes can be enabled with a PIN or a password to achieve the desired function for the respective scene.

In contrast to prior art solutions for frame accurate editing, which achieve it in a non-standard way, the above described embodiment of the invention is in conformance with the above-mentioned BD-RE standard. As maker data provided for in the BD specifications are used, the method is compatible with all implementations of the BD specifications. Enabled editing features with a PIN or a password allows for simple implementation to achieve the desired function for conditional access.

Applications and use of the above described method according to the invention are various and include exemplary fields such as the complete range of Blu-ray recording and playback products, such as consumer or professional BD recorders, BD storage solutions, etc. that can be enabled with a PIN or a password to achieve the desired function for the respective scene.

Further applications may also include any A/V storage applications that make use of a mark as explained above that can be enabled with a PIN or a password to achieve the desired function.

A further advantage is that the video payload is not edited and the foregoing described features are obtained using additional metadata of the video, i.e. skip-start mark positions and the maker defined data is additionally written to the disc and enabled with a PIN or a password to achieve the desired editing function. Embodiments can be implemented in any suitable form including hardware, software, firmware or any combination of these.

Further embodiments can be implemented as computer software running on one or more data processors and/or digital signal processors. The elements and components of an embodiment may be physically, functionally and logically implemented in any suitable and enabled with a PIN or a password.

Claims

In the Claims

1. A method of providing frame accurate conditional access on an audio-visual stream including employing at least one mark that identifies each of at last one segment within the AV stream; editing the segment identified by the mark; and providing a password to enable viewing of the segments.

2. The method according to claim 1, further including storing the mark within the AV stream.

3. The method according to claim 1, wherein the mark is a skip-start mark.

4. The method according to claim 3, wherein the skip-start mark defines a start and duration of a sequence of frames of said AV stream cut out during editing of said AV stream.

5. The method according to claim 1, further including storing the edited audio-visual stream with the segment identified by the mark on a storage medium to provide conditional access during playback of the segment.

6. The method according to claim 5, further including playing back the edited AV stream and prompting for the password to enable viewing of the segments.

7. The method according to claim 6, further including playing back the edited AV stream, if the password, is not correctly entered in a seamless manner by skipping frames between edit-in points and edit-out points established by the marker and playing back the edited AV stream if, the password is correctly entered, in a seamless manner by not skipping frames between edit-in points and edit-out points established by the marker.

8. An apparatus for conditional frame accurate access on an encoded A/V stream, said apparatus being adapted to perform the method according to claim 1, the apparatus including a device configured for setting a mark indicating a start and duration of a sequence of frames to be skipped from said AV stream when playing said edited AV stream.

9. The method of claim 1 wherein editing further comprises the creation of a virtual play-list for frame accurate conditional access for an MPEG stream.

10. The method of claim 9 wherein editing allows conditional access to any part of the MPEG stream ranging from just one frame to all frames that can be made conditional and viewed subject to the password.

11. A system for decoding an encoded AV stream (30) including: a decoder (31) for decoding the encoded AV stream (30) having a plurality of frames (34), wherein the decoder is configured to detect the frames (34) that contain a mark within the encoded AV; a storage device (33) configured to receive and store frames that have been decoded by decoder (31); an output device (35) to read frames (34) out of storage device (33); a selection mechanism responsive to detection by the decoder of the mark to not place those of the frames (34) indicated by the mark into storage device (33).

12. The system of claim 11 wherein the mark indicates a beginning and a duration of the frames indicated by the mark.

13. The system of claim 12, wherein the output device continues to read frames (34) out of storage device (33) that are not indicated by the mark.

14. The system of claim 13, wherein the decoder (31) is configured responsive to detection by the decoder of the mark to not place those of the frames (34) indicated by the mark into storage device (33) and to continue reading from the encoded stream (30) at the beginning of a first or last GOP, depending on playback direction, until the last frame indicated by the mark is reached.

15. The system of claim 14, wherein the decoder (31) is configured to place the frames (34) into the buffer (33) after decoding the last frame or first frame, depending on playback direction, indicated by the start mark to enable seamless playback at the output device (35).

16. The system of claim 11 wherein the storage device (34) arranged in a FIFO structure.

doa frame buffer (33) configured for storing decoded frames (34) from said decoder (31) and feeding an output (35) for decoded frames at nominal speed, wherein the decoder (31) is configured to stop feeding said buffer (33) and to continue reading from said encoded stream (30) at the beginning of a first or last_GOP, depending on the playback direction, in said cut-out section being indicated by a skip- start mark configuring said stream when said mark is reached, and to continue feeding said buffer (33) at nominal speed after decoding the last or first frame of said cutout section configured by said skip- start mark, depending on the playback direction, so that seamless playback skipping of said cut-out section is provided at said output (35).

17. The method according to claim 1, further including storing the mark within the AV stream.

18. A computer-readable medium having embodied thereon a computer program for frame accurate access to an encoded A/V stream, for processing by a computer, the computer program including: a first code segment for setting a mark indicating a start and duration of a sequence of frames to be skipped from the AV stream when playing the edited AV stream; and a second code segment for prompting for a password to enable viewing of the sequence of frames.

19. The computer program of claim 18, wherein said mark is a skip-start mark according to a blu-ray standard.

20. The computer program of claim 18 wherein the first code segment embed s the mark into the AV stream.