Rendering does not process transparency changes over time - Playing my timeline do. v2.79b Hello dear community :)

Note that I started with Blender less than 4 days ago.
I have a simple scene with 2 texts, 1 Sun light and another lamp light.
I managed to make the lamp light move so that shadows move as well - keyframes with location -
I have another text, rather flat, and I want its transparency to change during the animation. I converted this text into a mesh and then I was able to apply different transparency values which I was able to record with keyframes - property: available -

When I "play" my timeline I can see both the lamp moving and the transparency changing.
But....

When exporting the whole thing to a video or even a single image of my timeline, my transparency is not processed at all.

Do you have an idea of what is going wrong ? Are there special options to enable ?
Here is a short video of the blender interface with the timeline playing.
You can see the light moving behind and the transparency changing next to the point of view.

https://www.youtube.com/watch?v=z14QSAyHzVA
Thanks for the file, i didnt realise that you were using Blender Render, i cant help you with that because i only use cycles and eevee.  

If you want the retro-aesthetics of blender you could even use eevee and configure it that way, plus benfit from the rendering speed.  

In Cycles as in EEVEE you would do your animation via the Node-Editor and animate the facture of a mix shader that hast one diffuse and one transparent shader (with absolute white!) in it.