iOS视频编辑学习

模仿系统视频剪辑做的一个界面

总结

1、 CMTime的使用

自带一系列的计算方法，如：

减法

CMTimeSubtract(self.endC, self.beginC)

比较

if (CMTimeCompare(cTime, self.endC) >= 0)

除法

CMTimeMultiplyByRatio(t, (int32_t)index, (int32_t)total);

2、 AVPlayer seekToTime的坑

seekToTime有很大误差

[self.player seekToTime:self.beginC toleranceBefore:kCMTimeZero toleranceAfter:kCMTimeZero];

3、判断AVPlayer的播放状态

可以通过rate属性,rate还可以控制播放速度

/* indicates the current rate of playback; 0.0 means "stopped", 1.0 means "play at the natural rate of the current item" */
@property (nonatomic) float rate;

[object addObserver:self forKeyPath:@"rate" options:NSKeyValueObservingOptionInitial | NSKeyValueObservingOptionNew context:nil];

4、添加字幕时的问题

离线模式可以通过设置AVVideoCompositionCoreAnimationTool添加字幕,但是此方式对AVPlayerItem添加字幕失败了。参考如下,还没找到替代方案

/*!
    @class			AVVideoCompositionCoreAnimationTool

    @abstract		A tool for using Core Animation in a video composition.

 @discussion
   Instances of AVVideoCompositionCoreAnimationTool are for use with offline rendering (AVAssetExportSession and AVAssetReader), not with AVPlayer.
   To synchronize real-time playback with other CoreAnimation layers, use AVSynchronizedLayer.

   Any animations will be interpreted on the video's timeline, not real-time, so
		(a) set animation beginTimes to small positive value such as AVCoreAnimationBeginTimeAtZero rather than 0,
		    because CoreAnimation will replace a value of 0 with CACurrentMediaTime();
		(b) set removedOnCompletion to NO on animations so they are not automatically removed;
		(c) do not use layers associated with UIViews.
*/