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FLV and F4V video formats for FlashBy default, Adobe Media Encoder encodes video for use with Flash using the F4V video format using the H.264 video codec for use with Flash Player 9.0.r115 and later, and the FLV format using either the On2 VP6 codec for use with Flash Player 8 and later, and the Sorenson Spark codec for use with Flash Player 7 and later. To understand how Flash achieves high-quality video with low bandwidth requirements, you must 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 repeated from the previous frames. A temporally compressed frame is often called an interframe. H.264, On2 VP6, and Sorenson Spark are temporal codecs. Although many other codecs use spatial compression (for example, JPEG is a spatial codec), the efficient temporal compression of the H.264, On2 VP6, and Sorenson Spark codecs, among other features, distinguishes them from other compression technologies because these codecs require a much lower bitrate to produce high-quality video. It’s important to note that interframe codecs also use intraframes. Intraframes are used as the reference frames (key frames) for the interframes. Both the On2 VP6 and Sorenson Spark codecs always begin with a key frame. Each key frame 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 key frame. An important dependency of the key frame distance is that it affects the ability of Flash Player to seek (fast-forward or rewind) through an FLV or F4V file. Flash Player can only advance from key frame to key frame, so if you want to skip to different places and pause the frames, use a lower key frame distance value. If you want to advance to every frame in an FLV or F4V file, use a key frame distance value of 1. You set the keyframe distance in the Advanced section of the Video tab in the Export Settings dialog box. When you reduce the key frame distance value, raise the bitrate for the video file to maintain comparable image quality. You set the the bitrate in the Video tab of the Export Settings dialog box. H.264, On2 VP6, and Sorenson Spark video codecsWhen encoding video using Adobe Media Encoder, you can choose from three different video codecs with which to encode your video content for use with Flash Player:
F4V and FLV encoding presetsWhen exporting with Adobe® Media Encoder CS4, choosing the FLV | F4V format automatically makes available a list of associated FLV and F4V presets designed for particular delivery scenarios. Selecting a preset, in turn, activates the appropriate default options in the various settings tabs (Video, Audio, and so on). In most cases, one of the provided presets matches your output goals. However, you can also adjust the parameters of an existing preset and save it as a custom preset. The following table lists the encoding settings used when you select from the FLV | F4V presets. The table lists the dimensions of the video produced by a given preset, the video codec used, and the Flash Player version that supports it.
Exporting for Adobe Media PlayerAdobe Media Player is designed to play FLV files, either streaming from a server or played back from a local hard disk. With Adobe Media Encoder, you can export FLV files for playback in the Adobe Media Player. Select FLV | F4V from the Format menu in the Export Settings dialog box. Then, select specific settings to meet the requirements of the FLV host or your target audience. For information on selecting an FLV codec in the Export Settings dialog box, see About the On2 VP6 and Sorenson Spark Video Codecs on the Capturing And Encoding Video page on the Developer Center website. For information about choosing the best video, audio, encoding, and bit rate settings for your target audience, see the Flash video (FLV) bitrate calculator on the Developer Center website. For more information about exporting video for the Adobe Media Player, see www.adobe.com/go/lrvid4116_xp.
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