Flash Video Encoder User Guide

Flash Video Encoder User Guide > Supported video compression codecs for Flash Video

Supported video compression codecs for Flash Video

By default, Flash Video Encoder encodes video using the On2 VP6 codec for use with Flash Player 8 and later, and the Sorenson Spark codec for use with Flash Player 7. To understand how Flash achieves high-quality video with low bandwidth requirements, you should understand video compression.

There are two types of compression that can be applied to digital media: spatial and temporal. Spatial compression is applied to a single frame of data, independent of any surrounding frames. Spatial compression can be lossless (in which no data is discarded from the image) or lossy (in which data is selectively discarded). A spatially compressed frame is often called an intraframe.

Temporal compression identifies the differences between frames and stores only those differences, so that frames are described based on their difference from the preceding frame. Unchanged areas are simply repeated from the previous frame(s). A temporally compressed frame is often called an interframe.

Both the On2 VP6 and Sorenson Spark are interframe codecs. Although many other codecs use intraframe compression (for example, JPEG is an intraframe codec), the efficient interframe compression of the On2 VP6 and Sorenson Spark codecs, among other features, distinguishes them from other compression technologies because these codecs require a much lower data rate (also known as the bit rate) to produce high-quality video.

It's important to note that interframe codecs also use intraframes. Intraframes are used as the reference frames (keyframes) for the interframes. Both the On2 VP6 and Sorenson Spark codecs always begin with a keyframe. Each keyframe becomes the main reference frame for the following interframes. Whenever the next frame is significantly different from the previous frame, the codec compresses a new keyframe.

Flash CS3