AVAssetExportSession：操作無法完成

Question

我使用UIImagePickerController採取從MOV到MP4轉碼的視頻，但結果是：

轉碼失敗：操作無法完成

下面是代碼：

-(void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info { 
    NSString *mediaType = [info objectForKey:UIImagePickerControllerMediaType]; 
    NSLog(@"UIImagePickerController mediaType: %@", mediaType); 
    if ([mediaType isEqualToString:(NSString *)kUTTypeMovie]) { 
     NSURL *videoURL = [info objectForKey:UIImagePickerControllerMediaURL]; 
     AVAsset *asset = [AVAsset assetWithURL:videoURL]; 
     NSLog(@"Video Link:%@", [videoURL absoluteString]); 
     AVAssetExportSession *exportSession = [[AVAssetExportSession alloc] initWithAsset:asset presetName:AVAssetExportPresetPassthrough]; 
     if (nil == exportSession) { 
      @throw [NSException exceptionWithName:@"Unknown Error" reason:@"Couldn't create AVAssetExportSession" userInfo:nil]; 
     } 
     NSString *documentsDirectory = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES)objectAtIndex:0]; 
     NSString *destinationPath = [documentsDirectory stringByAppendingString:@"/output123.mp4"]; 

     NSLog(@"Dest: %@", destinationPath); 

     NSLog(@"Supported File Types: %@", [exportSession supportedFileTypes]); 
     exportSession.outputURL = [NSURL URLWithString:destinationPath]; 
     exportSession.outputFileType = AVFileTypeMPEG4; 
     exportSession.shouldOptimizeForNetworkUse = YES; 

     [exportSession exportAsynchronouslyWithCompletionHandler:^{ 
      switch ([exportSession status]) { 
       case AVAssetExportSessionStatusFailed: 
        NSLog(@"Transcode Failure: %@", [[exportSession error] localizedDescription]); 
        break; 
       case AVAssetExportSessionStatusCancelled: 
        NSLog(@"Transcode Cancelled: %@", [[exportSession error] localizedDescription]); 
        break; 
       default: 
        NSLog(@"Transcode Success, What's Next?"); 
        break; 
      } 
     }]; 
    } else { 
     NSLog(@"Not a Movie"); 
    } 
} 

我錯過了什麼？

這裏是控制檯輸出：

UIImagePickerController mediaType: public.movie 
Video Link:file://localhost/private/var/mobile/Applications/EAE27E83-0C27-4725-B606-13C9353B0FCB/tmp/capture-T0x1f56bf10.tmp.2mT0pL/capturedvideo.MOV 
Dest: /var/mobile/Applications/EAE27E83-0C27-4725-B606-13C9353B0FCB/Documents/output123.mp4 
Supported File Types: (
    "com.apple.quicktime-movie", 
    "com.apple.m4a-audio", 
    "public.mpeg-4", 
    "com.apple.m4v-video", 
    "public.3gpp", 
    "org.3gpp.adaptive-multi-rate-audio", 
    "com.microsoft.waveform-audio", 
    "public.aiff-audio", 
    "public.aifc-audio", 
    "com.apple.coreaudio-format" 
) 
Transcode Failure: The operation could not be completed 

Answer 1

你想用fileURLWithPath而不是URLWithString：

exportSession.outputURL = [NSURL fileURLWithPath:destinationPath]; 

更多信息，請參見this explanation。