The Progressive download information box aids the progressive download of an
ISO file. The box contains pairs of numbers (to the end of the box)
specifying combinations of effective file download bitrate in units of
bytes/sec and a suggested initial playback delay in units of milliseconds.
The download rate can be estimated from the download rate and obtain an upper
estimate for a suitable initial delay by linear interpolation between pairs,
or by extrapolation from the first or last entry.
author  Alexander Simm

The map contains pairs of bitrates and playback delay.
return  the information pairs