ios - AVAssetExportSession exportAsynchronouslyWithCompletionHandler返回失败

我正在实现AVAssetExportSession来在线修剪视频，但总是返回失败。

这是我的实现:

NSString *url = @"http://www.ebookfrenzy.com/ios_book/movie/movie.mov";
NSURL *fileURL = [NSURL URLWithString:url];
AVAsset *asset = [AVAsset assetWithURL:fileURL];
AVAssetExportSession *exportSession = [[AVAssetExportSession alloc] initWithAsset:asset presetName:AVAssetExportPresetHighestQuality];
NSURL *exportUrl = [NSURL fileURLWithPath:[documentsDirectory stringByAppendingPathComponent:@"export.m4a"]];

exportSession.outputURL = exportUrl;
exportSession.outputFileType = AVFileTypeQuickTimeMovie;
CMTime time = CMTimeMake(1, 10);
exportSession.timeRange = CMTimeRangeMake(kCMTimeZero, time);
[exportSession exportAsynchronouslyWithCompletionHandler:^(void) {

    switch (exportSession.status)
    {
        case AVAssetExportSessionStatusCompleted:
            /*expor is completed*/
            NSLog(@"Completed!!");
            break;
            case AVAssetExportSessionStatusFailed:
            NSLog(@"failed!!");
            /*failed*/
            break;
        default:
            break;
    }
}];

你们都知道为什么会这样或我做错了什么吗？

最佳答案

您正在尝试使用远程URL创建AVAsset，并且需要知道资产已加载，然后才能开始导出。
AVAsset符合AVAsynchronousKeyValueLoading协议，这意味着您可以观察tracks键并在值更改后开始导出:

NSURL *myURL = [NSURL URLWithString:myMovieURLString];
AVAsset *asset = [AVAsset assetWithURL:myURL];

__weak typeof(self) weakSelf = self;

[asset loadValuesAsynchronouslyForKeys:@[@"tracks"] completionHandler:^{

    //Error checking here - make sure there are tracks

    [weakSelf exportAsset:asset];

}];

然后，可以将导出代码放在单独的方法中:

- (void)exportAsset:(AVAsset *)asset {

    //Your export code here
}