sliding / scrolling texture - not smooth

Hi, I want to slide a single texture (repeated) on a videoplane by applying an offset to the "S" (x) texture coordinate. I have tried with a shader as the patch attached as a zip, aplying an offset and adding it to the s coordinate, but it does not work.

The effect I want is achieved with this using jit.scanslide, but it does not look good and smooth:

I would rather do it with openGL. Any suggestion/ideas?
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