DVD+VR - Technical Format Overview

Technical Format Overview

The DVD+VR format basically defines how to record video in a DVD-Video compliant manner to an optical disc. The resulting disc should, after finalization, play back on any DVD Video player that can physically read the media. The DVD-Video standard was never intended to be used for recording though, and in order to achieve the goal of making a DVD Video recorder, some tricks are needed when recording the disc.

For example: For the DVD video format, a recording is stored in an MPEG program stream, containing DVD-Video specific packets for navigation purposes—such as fast forward and fast reverse. In order to fill these packets properly, an encoding system needs to examine considerable amounts of video data, both before and after the navigation point. Video recorder systems typically have too little memory to achieve this fully, so logically a work-around for this has been introduced.

In order to allow editing, and building recording databases, next to the /VIDEO_TS directory that is present on any DVD Video disc, also a /VIDEO_RM directory is present, holding the recorder meta-data. To a regular video player this data is irrelevant, and such player will ignore it.

From a file system point of view, the media are very similar to regular DVD Video media. Both in finalized and in unfinalized form the disc contains a UDF file system, bridged with ISO 9660. For unfinalized DVD+R discs, this is hidden to the eye: the space for the file system and DVD Video data remains reserved and unrecorded at the start of the disc, until the disc is finalized.

The resulting file system also looks slightly different from what one would expect on most authored DVD Video discs. On authored discs there is typically one group of VOB files per title; whereas on a DVD+VR recorded disc a single VOB set is shared by all recordings. For a DVD Video player this makes no difference.