IndexLocation

Where a container keeps its seek index, in the published resource's own byte coordinates.

none requires positive evidence that the container declares no index. An empty index table at open is not that evidence — a Matroska's Cues live at the tail and the demuxer has not read them yet — so the honest answer for "we did not look, or we looked and could not tell" is unknown. The distinction exists because a client that read none would skip the tail reads entirely, and skipping them on a file that has Cues costs a keyframe-basis plan, silently.