Footage Basics

When working with footage, you should be aware of how frames are identified, clip duration, and frame rate.

Time and Timecode

Frames (and time) are identified in combustion in one of two ways: using numbered frames or SMPTE timecode.

With numbered frames, each clip is numbered starting at one and increments by one for each successive frame.

Timecode is the standard indexing method used for keeping track of video frames. The numbers in a timecode value denote hours, minutes, seconds, and frames (00:00:00:00) elapsed on a videotape.

Drop-frame timecode compensates for the small difference between theoretical 30 fps and the real-world NTSC frame rate of 29.97 fps. In drop-frame timecode, the first two frame numbers of every minute are skipped (or dropped). You can identify drop-frame timecode by the semi-colon between the seconds and frames (00:00:00;00).

Duration and Timelines

All layers, composites, and objects have durations. You can change the duration of a layer by adjusting the in point and out point in the Timeline.

The Timeline allows you to position layers and objects in time by providing a visible representation of the duration of the clips in addition to the total duration of the composite.

Frame Rate

The frame rate is the number of frames that are played back per second of a rendered composite. You can specify a different frame rate for each composite. Typically, the frame rate you assign to a composite depends on the type of rendered output you will generate. For film, use 24 fps. For video, use either 29.97 fps (NTSC) or 25 fps (PAL). If you are creating video for the web, you should use frame rates in the vicinity of 12 fps (lower than that produces jerky video).