Flash Video Encoder User Guide

Flash Video Encoder User Guide > Understanding video standards and terminology > Interlaced versus noninterlaced video

Interlaced versus noninterlaced video

If your source video is interlaced, you can use Flash Video Encoder to either maintain the interlacing, or deinterlace it during encoding to create noninterlaced video.

Most broadcast video is interlaced, though emerging high-definition television standards have interlaced and noninterlaced variants. Interlaced video consists of two fields that make up each video frame. Each field contains half the number of horizontal lines in the frame; the upper field (or Field 1) contains all of the odd-numbered lines, and the lower field (or Field 2) contains all of the even-numbered lines. An interlaced video monitor (such as a television) displays each frame by first drawing all of the lines in one field and then drawing all of the lines in the other field. Field order specifies which field is drawn first. In NTSC video, new fields are drawn to the screen approximately 60 times per second, which corresponds to a frame rate of approximately 30 frames per second.

Noninterlaced video frames are not separated into fields. A progressive-scan monitor displays a noninterlaced video frame by drawing all of the horizontal lines, from top to bottom, in one pass. Because of this, both fields that make up a video frame are shown simultaneously. Thus, a computer monitor displays video at 30 fps, and most video displayed on computer monitors is noninterlaced.

Typically you will always want to deinterlace video content used in Flash. Both the Sorenson Spark and On2 VP6 codecs used to encode Flash video can cause unwanted artifacts when encoding interlaced video.

There are instances when you may want to avoid deinterlacing: for example, if the source video doesn't contain too many interlacing artifacts (typically caused by horizontal pans or motion). When you deinterlace, you discard half of the video's vertical resolution.

You may also want to avoid deinterlacing if you're reducing the size of the video substantially--to 240 x 180 pixels or less--because the pixel averaging that occurs when resizing video to a smaller size can cause interlacing artifacts that appear as a motion blur.

Flash CS3