How would I go about doing the following:

I have a short 3d text animation from Cinema 4d, with a camera that tracks the text starting from the front and moving closer to the text and rotating to the left of it. I've exported this to after effects.

In AE, how do I go about replacing the front surface of the text (mask it) so I can replace it with a video. Essentially, I want the final product to be the video playing playing as if the front of the 3d text were a video screen, but I want the extruded 3d back of the text to remain intact so I don't like the 3d-ness.

Any ideas? One way would be to add another flat 2d layer in cinema4d right in front of the 3d text that I then replace using track mattes, but is there a better way?

Hi, you could import the video clip and use it as surface in C4d. Then render the surface only which should be pretty quick. Then overlay it in after effects.

Following Martin's suggestion, use the polygon selection in your text's material. Duplicate the material and specify C1 (cap 1). Import the video into the material's color channel. Then it will appear only on the front cap. Render. The downside is that the video will be baked into your text, leaving no flexibility for color correction or other adjustments.

There is probably a more elegant way to achieve this.

Another option is to make the text (MoText or extruded text, right?) editable, select only the caps to make them a separate object. Then add a compositing tag and assign an object buffer to that object. Render and composite in AE using a track matte.

HTH.