OK I figured it out.
Under the textures properties you have:
• Frames - This is the amount of frames in the animation, it gives you the option to Match the movies frames with the click of a button below. This field needs to be set to 1.
• Fields - Dunno what this does, didn’t touch it.
• Start - When the animation will first be active in the timeline. I set this to 1 for this example.
• Offset - This is the key to the technique.
(My animated texture is of a smoke puff, it is 50 frames long.)
- I set the Offset to 0 at frame 0 and keyed the frame
- Then I moved forward to the frame at which I wanted the texture to start to play, in this case frame 25 and again keyed the Offset to 0.
- Then I moved forward to a frame that would allow the full texture to play out, so in this case frame 75 (current frame time plus amount of texture frames)and then in the Offset keyed the value to 50 (The length of the texture animation)
- I then went to the next frame (frame 76) and keyed the offset back to 0, in effect resetting the animation to the start.
- In the curve editor this creates a natural rise from frame 25 (value 0) to 75 (value 50) and sharply back down at 76 (value 0).
I hope this helps someone in the future, I know it is probably an uncommon problem but it could be quite a powerful solution to animating facial textures.