Optional ReadonlysampleHow many packets of the track to measure timing over. The walk reads metadata only: on an ISO base media file the sample table is already in memory once the file opens, so raising this costs processing rather than bytes; on Matroska and MPEG-TS there is no such table and every packet costs a read of the media data itself.
Optional ReadonlyremoteWhether the bytes stand for a file that will be opened over a link. It is what makes a trailing index cost anything, and a probe run against a downloaded copy of a remote file has to be told.
Optional ReadonlyprogressiveWhether the caller can open a conversion's prefix while the rest is still being written. Such a source opens only at its beginning and cannot be seeked into, so this is true only where playback starts at zero.
How the caller intends to open whatever comes out.