淡入淡出可以使用FadeIn、FadeOut，具体使用方法见下面的原文～
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FadeIn (clip clip, int num_frames, int "color", float "fps")
FadeIO (clip clip, int num_frames, int "color", float "fps")
FadeOut (clip clip, int num_frames, int "color", float "fps")
FadeIn0 (clip clip, int num_frames, int "color", float "fps")
FadeIO0 (clip clip, int num_frames, int "color", float "fps")
FadeOut0 (clip clip, int num_frames, int "color", float "fps")
FadeIn2 (clip clip, int num_frames, int "color", float "fps")
FadeIO2 (clip clip, int num_frames, int "color", float "fps")
FadeOut2 (clip clip, int num_frames, int "color", float "fps")
FadeOut cause the video stream to fade linearly to black or the specified RGB color at the end. Similarly FadeIn cause the video stream to fade linearly from black or the specified RGB color at the start. FadeIO is a combination of the respective FadeIn and FadeOut functions. The sound track (if present) also fades linearly to or from silence. The fading affects only the last num_frames frames of the video. The last frame of the video becomes almost-but-not-quite black (or the specified color). An additional perfectly black (or the specified color) frame is added at the end, thus increasing the total frame count by one.
FadeIn0 / FadeOut0 do not include the extra frame. It is useful when processing Audio only clips or chaining two or more fades to get a square law or a cube law fading effects. e.g Clip.FadeOut0(60).FadeOut0(60).FadeOut(60) gives a much sharper attack and gentler tailoff. The 50% point is at frame 12 of the fade, at frame 30 the fade is 12.5%, at frame 45, 1.6% the effectiveness is more pronounced with audio.
FadeIn2 / FadeOut2 works similarly, except that two black (or color) frames are added at the end instead of one. The main purpose of this is to work around a bug in Windows Media Player. All the WMP versions that I've tested fail to play the last frame of an MPEG file - instead, they stop on the next-to-last frame when playback ends. This leaves an unsightly almost-but-not-quite-black frame showing on the screen when the movie ends if you use FadeOut. FadeOut2 avoids this problem.
The color parameter is optional, default=0 , and is specified as an RGB value regardless of whether the clip format is RGB or YUV based. See here for more information on specifying colors.
The fps parameter is optional, default=24.0, and provides a reference for num_frames in audio only clips. It is ignore if a video stream is present. Set fps=AudioRate() if sample exact audio positioning is required.
FadeOut(clip, n) is just a shorthand for Dissolve(clip, Blackness (clip, n+1, color=$000000), n) (or instead of n+1, n+2 for FadeOut2 and n for FadeOut0).
