更快地切割 AVAsset

Question

我有这个代码来剪切我的 AVAsset 视频：

AVURLAsset *asset = [AVURLAsset URLAssetWithURL:_url options:nil];

[[NSFileManager defaultManager] removeItemAtPath:[NSString stringWithFormat:@"%@",_url] error:nil];

AVAssetExportSession *exportSession = [[AVAssetExportSession alloc] initWithAsset:asset presetName:AVAssetExportPresetHighestQuality];

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *outputURL = paths[0];
NSFileManager *manager = [NSFileManager defaultManager];
[manager createDirectoryAtPath:outputURL withIntermediateDirectories:YES attributes:nil error:nil];
outputURL = [outputURL stringByAppendingPathComponent:@"output.mp4"];
[manager removeItemAtPath:outputURL error:nil];

exportSession.outputURL = [NSURL fileURLWithPath:outputURL];
exportSession.shouldOptimizeForNetworkUse = YES;
exportSession.outputFileType = AVFileTypeQuickTimeMovie;
CMTime start = CMTimeMakeWithSeconds(slider.min*(videoDuration-1), 600);
CMTime duration = CMTimeMakeWithSeconds(slider.max*(videoDuration-1), 600);
CMTimeRange range = CMTimeRangeMake(start, duration);
exportSession.timeRange = range;
[exportSession exportAsynchronouslyWithCompletionHandler:^(void) {
     switch (exportSession.status) {
         case AVAssetExportSessionStatusCompleted:

             _url = [NSURL URLWithString:[NSString stringWithFormat:@"file://%@",outputURL]];

             break;
         default:
             break;
     }

 }];

问题：将 AVAsset 保存到 URL 并重新加载它需要一段时间。有可能让它更快吗？

Answer 1

您可以使用 AVAssetExportPresetPassthrough 作为预设名称，而不是 AVAssetExportPresetHighestQuality。您也许可以通过这种方式避免昂贵的转码。设置时间范围可能排除某些格式的这种情况，但值得一试。

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