AVAssetImageGenerator - 在 5 秒时生成缩略图

Question

看起来很简单。我只想要视频 5 秒后的缩略图：

AVURLAsset *asset1 = [[AVURLAsset alloc] initWithURL:[NSURL URLWithString:url] options:nil];
AVAssetImageGenerator *generate1 = [[AVAssetImageGenerator alloc] initWithAsset:asset1];
generate1.appliesPreferredTrackTransform = YES;
NSError *err = NULL;
Float64 seconds = 5;
int32_t preferredTimeScale = 30;
CMTime actualTime;
CMTime inTime = CMTimeMakeWithSeconds(seconds, preferredTimeScale);
CMTimeShow(inTime);
CGImageRef oneRef = [generate1 copyCGImageAtTime:inTime actualTime:&actualTime error:&err];

输出是这样的：

Printing description of actualTime:
(CMTime) actualTime = 83 1000ths of a second {
  value = 83
  timescale = 1000
  flags = kCMTimeFlags_Valid
  epoch = 0
}
Printing description of inTime:
(CMTime) inTime = 150 30ths of a second {
  value = 150
  timescale = 30
  flags = kCMTimeFlags_Valid
  epoch = 0
}

为什么actualTime 与inTime 不同？？？如何在视频中获得 5 秒的图像？

Answer 1

尝试使用requestedTimeToleranceBefore 和requestedTimeToleranceAfter：

generate1.requestedTimeToleranceBefore = kCMTimeZero
generate1.requestedTimeToleranceAfter = kCMTimeZero

var requestedTimeToleranceBefore: CMTime

图像在请求时间之前的最大时间长度 可能会生成。

var requestedTimeToleranceAfter: CMTime

图像在请求时间之后的最长时间 可能会生成。