When choosing file size, the limiting factor is the size of the media to be used (such as 700MB for CD-R). The standards are designed such that a certain amount of content will fit on each piece of media, with the best possible quality in terms of size. If more discs are required for sufficient quality, the standard will define the circumstances where it is acceptable to expand to a second or third disc. Newer video standards moved away from the size constraints and replaced them with a quality based alternative such as the use of CRF.