QuickTime 4 Reference

TargetDataSize

An alternative way to view the quality-versus-size tradeoff is to specify a desired maximum data size and ask for a quality that does not exceed that size.

In QuickTime 4, the JPEG graphics exporter supports the TargetDataSize setting, which is implemented by compressing the image repeatedly, lowering the quality until the target size (or a maximum attempt limit) is reached.