设置 `AVAssetExportSession` 的 `fileLengthLimit` 会导致：“导出失败：无法打开”

Question

我正在尝试将 AVAssetExportSession 的大小限制为 10mb。不设置fileLengthLimit，则"Export is completed"。设置fileLengthLimit = 10*1024*1024后，"Export failed: Cannot Open".

 - (void) splitVideo{
     AVURLAsset *videoAsset = [AVURLAsset URLAssetWithURL:output options:nil];
     CMTime videoDuration = videoAsset.duration;

     CMTime start = CMTimeMakeWithSeconds(0, 1);
     CMTimeRange range = CMTimeRangeMake(start, videoDuration);

     NSString *outputPath = [NSTemporaryDirectory() stringByAppendingPathComponent:@"output1.mp4"];
     [self cutVideo:output withRange:range withOutput:outputPath];
}

 - (void) cutVideo:(NSURL *)url  withRange:(CMTimeRange)range withOutput:(NSString*)path{

    AVAsset *asset = [[AVURLAsset alloc] initWithURL:url options:nil];
    NSArray *compatiblePresets = [AVAssetExportSession exportPresetsCompatibleWithAsset:asset];
    if ([compatiblePresets containsObject:AVAssetExportPresetHighestQuality]) {
         AVAssetExportSession *exportSession = [[AVAssetExportSession alloc]
                                           initWithAsset:asset presetName:AVAssetExportPresetPassthrough];

         NSURL *finalUrl = [NSURL fileURLWithPath:path];
         exportSession.outputURL = finalUrl;
         exportSession.outputFileType = AVFileTypeMPEG4;
         exportSession.fileLengthLimit = 10*1024*1024;
         exportSession.timeRange = range;

         [exportSession exportAsynchronouslyWithCompletionHandler:^{
             dispatch_async(dispatch_get_main_queue(), ^{

             });
             if ([exportSession status] == AVAssetExportSessionStatusCompleted){
                 NSLog(@"Export completed");
             }else if ([exportSession status] == AVAssetExportSessionStatusFailed){
                 NSLog(@"Export failed: %@", [[exportSession error] localizedDescription]);
             }else if ([exportSession status] == AVAssetExportSessionStatusCancelled){
                 NSLog(@"Export canceled");
             }
          }];
     }
 }

正在导出的视频大约为 25mb。

Answer 1

我替换了

AVAssetExportSession *exportSession = [[AVAssetExportSession alloc] initWithAsset:asset presetName:AVAssetExportPresetPassthrough]

与：

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

AVAssetExportPresetPassthrough - "This export option will cause the media of all tracks to be passed through to the output exactly as stored in the source asset"

Answer 2

我在使用 AVAssetExportSessionPresetHighestQuality 或除 PassThrough 之外的任何预设时看到了这个错误（并且通过 passthrough 会话对我的视频没有影响，所以它没用）。原来我的输入视频是问题所在 - 我认为分辨率太高（几乎是 4k 宽度），切换到 1920x1080 视频为我修复了它。

设置 `AVAssetExportSession` 的 `fileLengthLimit` 会导致：“导出失败：无法打开”

Setting `fileLengthLimit` of `AVAssetExportSession` causes: " Export failed: Cannot Open"

ios

avurlasset

avassetexportsession

avasset