IFO files contain the formatting information of the VOB files, which tells the DVD player exactly how the DVD should be played (eg. aspect ratio, subtitles, languages, menus etc…). BUP files are backups for IFO files, which are needed if the IFO files gets corrupted. If you rip the DVD without IFO files, then the VOB files may not play correctly, or may not even play at all. Similarly for conversion, IFO files are essential since video converters like FlasKMPEG (which supports IFO parsing) will need them if you want to encode videos, or fix multi-angle ripping problems.
.IFO file: TitleSet
VTSI_MAT Managment table Containes basic information about the IFO file itself, and attribute information about the streams contained by the Menu-VOB file and the Title-Set VOB files.
PTT_SRPTI Chapter table Here you will find the definition of the Chapters. This table just holds pointers to PGC’s and Programs that you can find in VTS_PGCITI.
VTS_PGCITI TitleSet (Movie) Program table This is the main program table. It holds all information about the TitleSet (Movie), how it should be played, what cells are used in which order and so on.
VTSM_PGCI_UT Menu Program table This one is nearly the same as above, except it holds the information for the Menu VOB file.
VTS_TMAPTI Time Map table Very uninteresting table. You’ll never need to edit anything in here.
VTSM_C_ADT Menu Cell address table Containes a list of all Cell’s in the Menu VOB file VTS_xx_0.VOB.
VTSM_VOBU_ADMAP Menu Vob Unit address table Containes a list of all Vob-Units in the Menu VOB file VTS_xx_0.VOB.
VTSM_C_ADT TitleSet (Movie) Cell address table Containes a list of all Cell’s in the TitleSet (Movie) VOB files VTS_xx_1.VOB – VTS_xx_n.VOB.
VTSM_VOBU_ADMAP TitleSet (Movie) Vob Unit address table Containes a list of all Vob-Units in the TitleSet (Movie) VOB files VTS_xx_1.VOB – VTS_xx_n.VOB.