FFMpeg - Overlay Not Being Shown When Enable=between Parameter Is Added

I am using below command to add transitions effect between videos using overlays such that when one videos is about to finish, the overlay gets visible. Before showing overlays, I

Solution 1:

The overlay filter syncs both inputs by timestamps, so that second X of the overlay video is printed on top of second X of the main video. So, with a arg of overlay=0:0:enable='between(t\,7\,9)', ffmpeg will start by aiming to overlay overlay frame with timestamp 7.00 on top of main video with timestamp 7.00. If the overlay video is not that long, there won't be any effect.

The overlay video timestamps need to be modified to create the required sync.

[3:v]colorkey=0x00d800:0.1,scale=w=1080:h=1920,setpts=PTS-STARTPTS+7/TB[tr0];

The setpts shifts the first transition stream to start with timestamp 7. This can now be overlaid with enable='between(t\,7\,9)'.