When it comes to marketing your brand or business online, can you tell your story in 15 seconds? How about six?

That's all the time you have when you use one of the new short-video sharing apps available for iOS and Android devices. Vine was the first of these video apps, enabling you to shoot and upload videos no more than six seconds long and loop over and over. Not to be left behind, Instagram recently added video sharing to its digital photo app, and upped the time limit to a whopping 15 seconds per video. Instagram videos don't loop.

Then there's MixBit, which lets you shoot short videos but also enables editing of multiple clips into longer one- and two-minute videos. The service just launched last week.

Related: YouTube Founders Launch MixBit Video App to Rival Vine and Instagram

All of these services are mobile-only, with videos shot and shared from iPhones and other mobile devices. Vine and Instagram video, especially, are proving to be immensely popular. Vine, which is owned by Twitter, amassed 13 million users in its first four months on the market. Instagram Video was immediately available to the service's 130 million users, who uploaded more than five million videos in the service's first 24 hours.

But, let's be serious: What is up with the short videos? Are six seconds and 15 seconds arbitrary amounts of time? Or is there some method to this madness?

The short-video approach is designed to offer viewers a much different viewing experience than with traditional longer-form videos. Case in point are Vine's six-second videos, which are immediate and without pretense. They're also short enough to upload and view quickly, even on slower mobile connections. Instagram went for slightly longer videos that enable companies to upload new or existing 15-second commercials.

In practical use, Vine's shorter videos tend to inspire more creativity. Since you can start and stop recording for multiple shots, many companies are creating interesting stop-motion animations that showcase their products. The looping nature of Vine videos can also result in interesting effects as videos circle back into and through themselves. The "summer up" roller coaster video from Target is a perfect example of Vine's stop-motion and looping in action.

Instagram, on the other hand, is attracting more traditional promotional videos. You don't have to be as inventive to fit your message into a 15-second container and many companies appreciate the extra time to tell their stories and showcase their products. For example, this Starbucks video gives a short tour of the company's original Pike Place store.

Related: Why Video for Instagram Isn't a Vine Killer

Since both Vine and Instagram encourage social sharing, the most interesting videos can quickly go viral. It's not unusual to see popular Vine and Instagram videos popping up in Twitter and Facebook feeds. The sharing nature of both services offer the potential for significant customer engagement.
If you want to see how the different services require different approaches, check out Gap's stop-motion videos on Vine and Gap's more traditional customer testimonials on Instagram.

What can you do in six seconds to promote your brand? Leave links to your short videos in the comments below.