As the pine decomposes, it may take nitrogen from the soil. It would make great mulch, though. If you want to compost the pine, it may be better to heap it up with an equal amount of green waste - lawn clippings, vegetable waste, etc. If you make a pile of one cubic yard, it will generate enough heat to compost fairly quickly. Then you will have plenty of compost to fill your beds in the spring. Having a pile of at least one cubic yard is important to generate heat. Spread out over the ground, it will take much longer for the bark to break down.

Here is a link that might be useful: Composting video series

What length and width are your beds going to be? At 24" high, they are 2/3 way to being a yard tall. Filling them with a mix of the pine mulch and greens...mowed grass, coffee grinds, veggie scraps etc, could make a good insitu compost pile. You could pile it a foot higher than your bed to get to the cubic yard size. It should stay in place and be ready to spread out to other areas as mulch or bed filling by spring. You could then top each bed off with Mel's mix. I had a lot of pine trees cut down several years ago (was infested with pine beetles). I spread the chipped branches all around my yard as mulch and found that it decomposed pretty rapidly.