duration_limit
Description:
The maximum duration that can be *currently* set for the clip, taking into account the in_point, max_duration, active, and track properties of its children, as well as any time effects.
If there is no limit, this will be set to CLOCK_TIME_NONE.
Note that whilst a clip has no children in any tracks, the limit will be unknown, and similarly set to CLOCK_TIME_NONE.
If the duration-limit would ever go below the current duration of the clip due to a change in the above variables, its duration will be set to the new limit.