Subtitles of the Movie

In this tutorial I'm going to introduce some basic concepts relating to encoding. In the Flash Video environment, Encoding refers to starting with a large video file and using that as the basis to create a smaller video file in a different format, and typically we start with a QuickTime, an AVI, or an MPEG file, and we create an FLV or an F4V file, and Flash can only use the FLV or F4V files, so that's why we need to perform that translation. And the job of translating from one format to another is performed by a coder-decoder, a codec. The decoder part of that is that when it comes time to play the file back you need to decode it, and the codec also does that. A very important part of encoding is creating keyframes. A keyframe is a frame in which all of the information is present to fully display that frame, and the term Key Frame is used in a number of different environments. Let's take a look at the definition of that in Wikipedia. They talk about animation and filmmaking. If we look at the contents we have animation here, computer graphics, video editing; the context we're looking at it here in is video compression, so let's take a look at that. A keyframe, also known as an Intra Frame, is a frame in which complete image is stored in the data stream and then after that only changes that occur from one frame to the next are stored and that greatly reduces the amount of information that has to be stored. Now, when a drastic change occurs, then we may need to have another keyframe because we can't easily define that just in terms of changes from one frame to the next. In addition, you can only fast forward or rewind to a Keyframe, so actually we want to have keyframes at regular intervals throughout the video to provide ourselves with points that we can Fast Forward to or Rewind to. You may be familiar with the term Keyframe from animating in Flash. So, let me go to the Timeline here. I'll just select this one object. If I right-click here and create Motion Tween, now if I move this object it creates a keyframe, that's that little black. right there Ð that's a keyframe, and this is also a keyframe. So, in Flash Animation the position of this object is fully defined here and it's fully defined at that final keyframe. In between that we have in between frames. So, that's the term Keyframe in terms of Flash Animation, and the meaning is very similar in Flash Video. And that concludes this tutorial on Encoding, and in the next tutorial we'll be taking a look at some different codecs that you can make use of in Flash.