VOB (Video OBject) is a container format used to store DVD files. It will usually have a .vob extension.
The contents of the VOB container is exactly the same as a standard DVD disk. This is a restricted subset of MPEG-2 which includes optional MPEG audio at 48K sample rate. VOB has extensions that can also contain LPCM (linear pulse code modulation), AC-3 (Dolby digital) or DTS audio formats and subtitles and menus. VOB permits up to 8 audio channels with 1 video channel.
On a DVD, all the content for one title is contiguous, but broken up into 1 GB (or less) VOB files in a computer compatible file system. The codec is H.262. The DVD also contains side files containing metadata and navigation information.
The DVD resolution for NTSC is 720 x 480 pixels (Pal 720 x 576). The aspect ratio is either 4:3 or 16:9. Modern DVD's use horizontal compression (anamorphic) on the video image while maintaining the full 480 pixel vertical resolution. Higher aspect ratios for movies are achieved by expanding the image on playback while maintaining the correct aspect ratio. The resulting black bars at the top and bottom are generated by the DVD player. This capability is shown on the DVD description by saying that it is "enhanced for use on widescreen TVs." Some early DVD's only supported the 4:3 aspect ratio and showed widescreen images using black bars that are in the video itself resulting in significant loss of vertical resolution for the video image. These DVD's will also be badly distorted on a 16x9 display screen.
This is the newer format specification defined for Blu-Ray devices. BD-ROM requires support for three formats:
- MPEG-2 part 2 and will usually have a .m2ts extension. About 2 hours of can be placed on a single disk in this format. However, this provides backward compatibility with DVD's which can be played on the same machine.
- H.264 also known as MPEG-4 AVC (Advanced Video Coding) codec. H.265 is the newest format available on some devices.
- VC-1 is an advanced high compression format. It can provide capacities of over 3 hours on a standard disk. Note this is the same format originally released as WMV version 9 by Microsoft.
Blu-Ray supports HD video at full 1920 x 1080 interlaced at 50 or 60Hz. Blu-Ray can support 1920 x 1080 Progressive at 24 frames/sec if the TV supports it. Newer devices can do 30Hz and some even 60Hz.