If you want to shoot HD video, not just any memory card will do. Quite simply, you need a card that’s fast enough to support the transferring of the video frames from camera to storage. If you try to use a slower card, the capture could fail or the camera might even refuse to record. The tricky part is knowing what card speed you need.
Camera memory manufacturers use a baseline standard of 150 KB/s of throughput to describe their cards. So a 1X card can only record and play back data at 150 KB/s. For video, use the fastest card that you can afford. For most cameras, you’ll need to use those rated 133X and above. Having an even faster card can come in handy when shooting still images in burst mode (such as timelapse applications). Be sure to compare speed and capacity when evaluating cards for purchase.