solved Overlaid video plays as black in preview

[RabbitEars]

I'm trying to overlay a video (.mp4 I downloaded from Youtube; plays fine by itself / outside of Videopad). It's meant to be the 3rd video track, showing up on top of tracks 1 and 2 (which are laid out side by side).

This track 3 video 'appears' normally in the top left window where all the files are reposited.

But in 'clip preview' I just see the checkboard background (peeping out from behind 1&2).

In 'sequence preview' I just see Tracks 1 & 2 (but there's a dotted line around so clearly Track 3 is registering). 

In the bottom window, where the timeline is, Track 3 appears as a solid grey bar (but I can see the thumbnails of 2 & 3).

I've shared the intended video for Track 3 below ('Video to be overlaid')

Any help would be appreciated.

Video to be overlaid

[borate]

Can't spot an issue with this, using the split-screen effect 2x2 grid for tracks 1 and 2 with your sky clip on track 3, scaled and positioned via the MOTION effect.  A thin blue border has been added for definition.

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Please share the project, so someone can see what you see.  It's easy, quick and can be private.  Just follow these four steps carefully...

•     Back up --- With your project on the timeline, click on MENU at the top-left.  Click FILE|BACK UP PROJECT FILES TO FOLDER.  Choose a folder and SELECT FOLDER.
•     Upload ---  Upload the saved, numbered FOLDER.  Use a free server - Google Drive, MS OneDrive, etc.*  Do NOT upload the individual VPJ or export file. 
•     Get link --- Get a public link.  If using Google Drive click GET SHAREABLE LINK. Change "restricted" to "anyone with the link can view"  Click COPY LINK | DONE.
•     Share ---    Paste that link here, or click the folder at the top-right of this forum to message it privately to me.  It won't be shared.

          *    Before uploading, right-click the folder, click PROPERTIES.  Look at the File Size to confirm that it's not too big for the free space on the server.

[RabbitEars]

I've just noticed that Tracks 1 & 2 have the bright green tick but Track 3 doesn't.  All are loaded on my timeline.

Sorry, ignore the immediate previous message. The green tick is there.  (Project submitted via PM)

[borate]

Click the FX button on the 'space' track 3 clip and use the MOTION effect to scale and position it, if this is what you have in mind.  Picture-in-picture.

All tracks should align, one atop of the other.  The overlay is shorter than the background and music, so it needs to be lengthened.

[RabbitEars]

Actually I'd like the night sky to fill the whole screen then fade out to reveal the pianos. I do know how to scale and position - that's how I managed to situate the pianos, so that's something at least (although I do it via 'scale' and 'position' separately in the FX box). Thanks also for pointing out the length discrepancy; I had indeed intended to clip Track 3 so that's not an issue. 

The problem is the visual - I just can't get what you managed to achieve though. I get the feeling it's something very noob and obvious that I've missed so it's rather frustrating. I'll keep trying. 

Thank you for your help. If you think of something please do let me know. 

[borate]

Add the TRANSPARENCY effect to track 3.  At the head, set opacity to zero.  Move the scrubber (red line) to where you want the fade to begin and click the small green + sign, to set a keyframe.  Move the line to where you want the fade to end and drag the blue line in the effects graph to the bottom, or set the slider at 100%.

  The result will look something like this...    

Sky remains on screen for a short time, then fades out.  The closer the keyframes (squares on the blue line) are to one another - horizontally - the quicker the fade.

[RabbitEars]

It is very odd, but everything is now working. I removed the track 3 file from the repository then re-loaded it (this is probably the 5th time I'm doing it, excluding several reboots of my PC) but suddenly it's working. 

I assume the little green men in my PC were on a lunch break or something. 

Hopefully there'll be no more issues.

Thank you very much for your help again.