Subtitles of the Movie

Compressing your video correctly will be an important skill if you plan to work with video in your Flash projects. So in this movie I give you some compression theory and practical tips and techniques to keep your video workflow running smooth and your video files as small as possible. For starters, it's important to import with the best quality video as possible and video with a minimum amount of motion between and within frames. Central to an understanding of why this is so is an understanding of the way that video is compressed. So let me give you some theory here. Video is basically a three-dimensional Array of color pixels. Two dimensions serve as spacial, which is horizontal and vertical directions of the moving pictures and one dimension represents the time domain, also referred to as temporal. A frame is a set of all pixels that correspond to a single point in time. Basically a frame is the same as a still picture and video is the quick display of one frame after the next. Now, video data often contains information that is repeated from frame to frame. That's what this illustration is trying to convey. These pixels here perhaps are repeated for a variety or a number of frames. This phenomenon is referred to as spacial and temporal redundancy. These similarities can be encoded by merely registering the differences within a frame and or between frames so the differences within a frame is referred to as spacial and that between frames, temporal. Compression works better if most pixels stay the same for a number of frames. So imagine this is a tree here and if the tree is blowing and these green pixels are alternating between the green of the leaves and the blue of the sky. That's not going to give you very good temporal compression since from frame to frame almost all the pixels will be changing. Instead, if you have a background of a solid wall, like a brick wall, that isn't moving, most of the pixels will be staying the same so you'll get very good temporal compression. One of the most powerful techniques for compressing video is called inter-frame compression, which works by comparing each frame in the video with the previous one. If the frame contains areas in which nothing has moved, no new data needs to be captured and the system simply issues a command that copies that part of the previous frame into the next one. Here is an example of two frames; very little difference. I think the position of the ping-pong ball is the only difference so you can see why this type of situation can create great compression results. Today's vide compressors also use a method of dropping frames and then encoding a series of fully uncompressed frames. These uncompressed frames, called keyframes, are used to calculate and rebuild the missing frames during playback, thus also drastically reducing the final size of the video. With all this manipulation of the original video signal, you can imagine how quickly and easily a video image can be degraded. This is why it's very important when applying any kind of compression to your videos that you always start with the highest quality video possible. By default, the Adobe Media Encoder exports encoded video using the On2 VP6 video Codec for use with Flash Player 8 and later. And the Sorenson Spark Codec for use with Flash Player 7 and earlier. A Codec is an algorithm that controls the way that video files are compressed and then decompressed during import and export. Only Flash Player 8 and later supports both publish and playback of On2 VP6 video and the On2 video Codec is the preferred video Codec to use when creating Flash content that uses video. You can see this here in the Export Settings Dialog that I covered earlier for the Adobe Media Encoder. In the Video Tab, notice that the Codecs here, Sorenson Spark or On2 VP6, the On2 VP6 Codec provides the best combination of video quality while maintaining a small file size. So there you have an introduction to some video compression theory underscoring the importance of using the best quality video as possible and video that contains the least amount of movement between and within frames and why you want to use the On2 VP6 Codec whenever possible. That will conclude this section of the tutorial on working with video, which brings us to the next section, applying behaviors. We'll learn how to use behaviors, how to set up an edit behaviors using the behaviors panel. You'll learn about mouse events and then the section concludes with a survey of several useful behaviors.