AVAssetImageGenerator复制图像失败 [英] AVAssetImageGenerator fails at copying image

问题描述

我正在使用AVAssetImageGenerator从视频的最后一帧创建图像.这通常可以正常工作，但copyCGImageAtTime有时会因错误

I am using AVAssetImageGenerator to create an image from the last frame of a video. This usually works fine, but every now and then copyCGImageAtTime fails with the error

NSLocalizedDescription = "Cannot Open";
NSLocalizedFailureReason = "This media cannot be used.";
NSUnderlyingError = "Error Domain=NSOSStatusErrorDomain Code=-12431";

我正在验证AVAsset不是零，并且我是直接从资产中拉出CMTime，所以我不明白为什么这种情况一直在发生.仅当尝试获取最后一帧时才会发生这种情况，如果我改用kCMTimeZero，它似乎可以工作.

I am verifying that the AVAsset is not nil and I'm pulling the CMTime directly from the asset, so I do not understand why this keeps happening. This only happens when trying to get the last frame, if I use kCMTimeZero instead, it seems to work.

- (void)getLastFrameFromAsset:(AVAsset *)asset completionHandler:(void (^)(UIImage *image))completion
{
    NSAssert(asset, @"Tried to generate last frame from nil asset");
    AVAssetImageGenerator *gen = [[AVAssetImageGenerator alloc] initWithAsset:asset];
    gen.requestedTimeToleranceBefore = kCMTimeZero;
    gen.requestedTimeToleranceAfter = kCMTimeZero;
    gen.appliesPreferredTrackTransform = YES;
    CMTime time = [asset duration];
    NSError *error = nil;
    CMTime actualTime;

    CGImageRef imageRef = [gen copyCGImageAtTime:time actualTime:&actualTime error:&error];
    UIImage *image = [[UIImage alloc] initWithCGImage:imageRef];
    NSAssert(image, @"Failed at generating image from asset's last frame");
    completion(image);
    CGImageRelease(imageRef);
}

这似乎相关，但并没有解决我的问题.

This seems to be related, but it did not solve my problem.

推荐答案

没有任何办法可以保证资产的 video 轨道位于[asset duration].它的持续时间可以短于整个资产.由于您将公差设置为kCMTimeZero，因此唯一可能的解决方法就是失败.

Nothing guarantees that your asset's video track exists at [asset duration]. It's duration can be shorter than the whole asset. Since you set the tolerance to kCMTimeZero the only possible resolution is failure.

编辑:为澄清起见，当资产的音频轨道比视频轨道稍长时，就会出现此问题.

To clarify, the issue emerges when you have an asset with audio track slightly longer than the video track.

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