in_point

The initial offset to use internally when outputting content (in nanoseconds, but in the time coordinates of the internal content).

For example, for a VideoUriSource that references some media file, the "internal content" is the media file data, and the in-point would correspond to some timestamp in the media file. When playing the timeline, and when the element is first reached at timeline-time start, it will begin outputting the data from the timestamp in-point **onwards**, until it reaches the end of its duration in the timeline.

For elements that have no internal content, this should be kept as 0.