How the files in VIDEO_ST directory work together?

If you look at the files in VIDEO_ST directory on a DVD movie disc, they can be divided into 3 groups.

1. The first group is named as VIDEO_TS.* and is the first item to be played by the DVD player application. VIDEO_TS.* usually contains advertisements, copyright notice, and a VMG menu to allow viewers to select language options, subtitle options, main movie and trailers.

02/06/2006  09:58 PM            14,336 VIDEO_TS.BUP
02/06/2006  09:58 PM            14,336 VIDEO_TS.IFO
02/06/2006  09:58 PM       208,343,040 VIDEO_TS.VOB

2. The second group is named as VTS_01_x.*, presenting the first TS (Title Set) video on the disc. VTS_01_x.* is usually the main movie video. As a title set, VTS_01_0.IFO and VTS_01_0.VOB provide the configuration information and on the screen menu. VTS_01_1/2/3/4.VOB contain the main movie video in 4 segments.

02/06/2006  09:58 PM            75,776 VTS_01_0.BUP
02/06/2006  09:58 PM            75,776 VTS_01_0.IFO
02/06/2006  09:58 PM        27,951,104 VTS_01_0.VOB
02/06/2006  09:58 PM     1,073,709,056 VTS_01_1.VOB
02/06/2006  09:58 PM     1,073,709,056 VTS_01_2.VOB
02/06/2006  09:58 PM     1,073,709,056 VTS_01_3.VOB
02/06/2006  09:58 PM       777,996,288 VTS_01_4.VOB

3. The third group is named as VTS_02_x.*, presenting the second TS (Title Set) video on the disc. VTS_02_x.* is usually an extra feature of the movie like the behind-the-scenes footage or documentaries. Like a main title set, VTS_02_0.IFO and VTS_02_0.VOB provide the configuration information and on the screen menu. VTS_02_1.VOB contain the video of the extra feature.

02/06/2006  09:58 PM            20,480 VTS_02_0.BUP
02/06/2006  09:58 PM            20,480 VTS_02_0.IFO
02/06/2006  09:58 PM            10,240 VTS_02_0.VOB
02/06/2006  09:58 PM       343,183,360 VTS_02_1.VOB