Recognizing Timeline downstream effects of changing time

1. Open 12-6.prproj.
2. Right-click the chase in fog clip --> choose Speed/Duration --> change the speed to 50% --> click OK
The back part of the clip is trimmed.
3. Press Ctrl+Z
4. Right-click the chase in fog clip --> choose Speed/Duration --> change the speed to 50%  and select the Ripple Edit, Shifting Trailing Clips--> click OK
The 1st clip is complete.
The 2nd line 視訊短 should be 視訊軌。
Toggle Sync Lock ??? There is only one track in this sequence.