HD Formats: 60i? 24p? 50i? 30p?

by Bob Hayes

60i? 24p? 50i? 30p? What's it all mean, and how can I use it?

By Bob Hayes, Artbeats' Director of Technology

It's been said the wonderful thing about standards is that there are so many of them. This is especially true for High Definition footage.

The ATSC (Advanced Television Systems Committee) originally specified no fewer than 18 different valid HD formats for use in North America in Table 3, with various combinations of aspect ratio, frame size and frame rate. In the first part of this century, different companies decided on different implementations of the Table 3 standards, with 1080/60i and 720/24P emerging as two of the most popular. Both have advantages and disadvantages. One nice thing is that it's fairly straightforward to use Artbeats HD footage in projects with these settings. Sometimes a little bit of manipulation is required to get Artbeats 1080/30P to work with 24P footage.

Until recently, Europe had yet to really jump on the HD bandwagon. At IBC this past September, I saw plenty of HD. Most European countries have at least one terrestrial HD broadcaster and sales of HD sets are climbing. However, the flavor of HD that seems popular in Europe is 1080/50i. This means 25 interlaced frames per second, just like PAL, but at a much higher resolution of 1920x1080. Yet another standard.

So, how can you use Artbeats footage in a project that will be used everywhere in the world, without resorting to a hardware standards converter? The solution is 1080/24p, and it's not difficult to do, depending on the content you have chosen.

Basically, what you need to do is force your video editing software to keep every frame of the clip, but to play them at 24fps instead of 29.97fps. For most Artbeats footage, this works very well. Explosions and pyro effects last a little longer, aerial sequences look like the aircraft is moving a little slower, etc etc. There are a few "people" shots that this may not work for, but many of these are easily fixed as well. We'll get to that in a minute.

How you go about forcing your NLE to slip the framerate depends on the software. If you happen to be compositing in After Effects, it's very simple to do. Just import the 29.97fps clip and then select it in your bin and choose "Interpret Footage." Set the frame rate to 24p or 23.98, depending on your project. Now, the clip will play the same quantity of frames, eliminating the problem of dropped frames that will sometimes arise if you simply drag a 29.97fps clip into a 24fps timeline. Other packages often have similar features, but if all else fails, you can export a frame sequence using QuickTime Player Pro and then re-import the sequence at the correct frame rate.

Many Artbeats Lifestyles clips were originally shot on 24fps film. For those clips, this trick may not work very well because people would be walking too slowly, giving them a "walking on the moon effect." Generally, 3:2 pulldown was applied to make the clip 29.97fps and all you need to do is remove the pulldown. Then you'll have a pristine 24fps clip! However, some Artbeats footage is shot on HD-CAM or even film at 30fps, so there is no pulldown to remove. The Artbeats web site offers more detailed clip information for frame rates, source and field rendering. You can also contact us if you have further questions.