I recorded such a video to show my usage, basically this is a vertical bar move according to the video play and seek to corresponding frame number. But the fact is that even we only need to refresh the vertical bar, the render() function still refresh the whole chart, that would consume huge CPU usage.
I would suggest to separate the vertical element to another hover canvas to reduce the re-render overhead, that would make a lot of real time chart possible.
Since we are already in the middle of our current plans, it might not be possible to consider these behavioral changes immediately. However we will revisit the behavioral changes in future releases and we will consider your suggestions at that point of time.