New video background is not working

Hi there, (I’m sorry if my english is not right}

I made a animation with camera tracking: a dinosaur running and roaring in front of a reallife person. It worked and I was proud of the results, like shadow catcher, animation, and so on…
Now I wanted to replace the background video with a different video (same file type). In render view the background was the right video I wanted, but when I rendered a picture I the background didn’t show my video. Just a gray color. Help! I don’t know what I did wrong or what settings I need to turn on or off.

Everything worked with the previous video, but after replacing it the video did not render. Only my 3d object.

Can anyone help me? I’ll be so thankful!
Btw: I’m not a pro, so I need a little description of the solution XD

I am not sure how you inserted your video clip, but it sounds like you inserted your video as a camera background.

You have two options that stand out to me, and there are probably more that I am not thinking of.

A) You could create a plane that lines up with the camera and apply an emit shader, with the video piped into the shader through the image texture node…

B) You could use blender compositor, and Do an alpha over to merge the video with the render. Just make sure to Set World Background To transparent, by going to Render > Film and selecting Transparency in the properties panel.

I hope this helps…