Storage medium including text-based caption information, reproducing apparatus and reproducing method thereof

This application is a continuation application of U.S. application Ser. No. 10/954,356 filed Oct. 1, 2004, now pending, and claims the priorities of Korean Patent Application No. 2003-68336, filed on Oct. 1, 2003, and No. 2003-87554, filed on Dec. 4, 2003 in the Korean Intellectual Property Office, the disclosures of which are incorporated herein in their entireties by reference.

1. Field of the Invention

The present invention relates to reproduction of data on a storage medium, and, more particularly, to a storage medium containing text-based caption information compatible with the subpicture method of a digital versatile disc (DVD) and the presentation method of a Blu-ray disc, and a reproducing apparatus and reproducing method thereof.

2. Description of the Related Art

Among conventional caption technologies, there exists text-based caption technologies, which are mainly used in a personal computer (PC), and a subpicture-graphic-based caption technology, which is used in a DVD.

First, as examples of the conventional text-based caption technologies mainly used in a PC, there are Synchronized Accessible Media Interchange (SAMI) of Microsoft, and Real-text technology of RealNetworks. The conventional text-based caption technologies have a structure in which a caption is output on the basis of synchronization information in relation to a file in which video stream data is recorded, or video stream data provided on a network.

FIG. 1 is a diagram illustrating the structure of a caption file used in a text-based caption technology mainly used in the conventional PC.

Referring to FIG. 1, there is a text-based caption file for video stream data, and a caption for video stream data is output on the basis of synchronization time information, for example, <sync time 00:00>, contained in the caption file. An example of a caption file constructed assuming continuous reproduction of the video stream data is shown.

FIG. 2 is a diagram illustrating the structure of an apparatus reproducing the conventional text-based captions.

Referring to FIG. 2, a text caption file is read from a storage medium 200, stored in a text caption data and font data buffer 220, and then converted into bitmap image graphic data by a text caption decoder 222. By control of a graphic controller 224, the converted graphic data is output on the screen 232 overlapping video frame data from a video frame buffer 214 that has been decoded in a video decoder 212.

However, as shown in FIG. 2, the conventional text-based caption file structure considers only synchronization time (<sync time=00:00>) by which a caption is displayed on the screen, and the type, size, and color of font when a caption is output on the screen, but does not consider how long a bitmap image is kept in a buffer after the bitmap is generated by decoding text caption data. Accordingly, there is a problem such that in a reproducing apparatus using a low speed processor, a caption cannot be output on the screen in real time as the conventional DVD reproducing apparatus reproduces data.

Meanwhile, the subpicture-graphic-based caption technology used in the conventional DVD will now be explained.

A DVD uses a bitmap image for a subtitle. Subtitle data of a bitmap image is losslessly encoded and recorded on a DVD. A maximum of 32 losslessly encoded bitmap images are recorded on a DVD.

FIG. 3 is a diagram illustrating the data structure of the conventional DVD explaining the structure of a caption file used in a subpicture-graphic-based caption technology used in the conventional DVD.

Referring to FIG. 3, in a DVD, the disc area is divided into a video manager (VMG) area and a plurality of video title set (VTS) areas. Title information and information on title menus is stored in the VMG area, and information on the title is stored in the plurality of VTS areas. The VMG area is formed with 2˜3 files, and each of the VTS areas is formed with 3˜12 files. The VMG area includes a VMGI area storing additional information on the VMG, a video object set (VOBS) area storing moving information (video objects) on a menu, and a backup area (BUP) of the VMGI. These areas are stored as one file and among them the presence of the VOBS area is optional.

In a VTS area, information on a title that is a reproduction unit, and a VOBS having moving picture data is stored. In one VTS, at least one title is recorded. The VTS area includes video title set information (VTSI), a VOBS having moving picture data for a menu screen, a VOBS having moving picture data of a video title set, and backup data of the VTSI. The presence of the VOBS to display the menu screen is optional. Each VOBS is again divided into recording units of a VOB and Cells that are recording units. One VOB is formed with a plurality of Cells. The smallest recording unit mentioned in the present invention is the Cell.

FIG. 4 is a diagram illustrating a detailed structure of the VOBS having moving picture data in the data structure of the conventional DVD shown in FIG. 3.

Referring to FIG. 4, one VOBS is formed with a plurality of VOBs, and one VOB is formed with a plurality of Cells. A Cell is again formed with a plurality of video object units (VOBUs). A VOBU is data encoded by a moving picture experts group (MPEG) method that is a moving picture coding method used in a DVD. According to the MPEG, since images are coded through spatiotemporal compression, a previous or succeeding image is required to decode a predetermined image. Accordingly, in order to support a random access function by which reproduction starts from an arbitrary position, intra coding that does not require a previous or succeeding image is performed in each predetermined interval. In the MPEG, this is referred to as an intra picture or I picture, and pictures between this I picture and the next I picture are referred to as a group of pictures (GOP). Usually, a GOP is formed with 12˜15 images.

Meanwhile, the MPEG defines system coding (ISO/IEC13818-1) to combine video data and audio data into one bitstream. The system coding defines two multiplexing methods: a program stream (PS) multiplexing method for optimization to generate one program and store in an information storage medium, and a transport stream (TS) multiplexing method appropriate to generate a plurality of programs for transmission. The conventional DVD employs the PS coding method.