iphone - AVAssetExportSession dealloc 在 iOS 4.3 中崩溃

Question

更新:我认为问题是内存不足；它不是。此错误在 4.3 中始终发生，而在 4.1/4.2 中即使在内存非常低的情况下也不会发生。

这是在一个小型 Objective-C 库中，我必须为主要是 Monotouch 应用程序编写——AVFoundation 尚未完全绑定(bind)。

这是跟踪:

0   Orbiter                             0x007977d8 mono_handle_native_sigsegv + 404
1   Orbiter                             0x007746b4 mono_sigsegv_signal_handler + 348
2   libsystem_c.dylib                   0x34ce472f _sigtramp + 42
3   AVFoundation                        0x365b3ab5 -[AVAssetExportSession dealloc] + 164
4   CoreFoundation                      0x34bc2c43 -[NSObject(NSObject) release] + 30
5   AVFoundation                        0x365b3607 -[AVAssetExportSession release] + 62
6   CoreFoundation                      0x34bdd047 sendRelease + 14
7   libsystem_blocks.dylib              0x312c292f _Block_object_dispose + 118
8   AVFoundation                        0x365b45b3 __destroy_helper_block_5 + 22
9   libsystem_blocks.dylib              0x312c288f _Block_release + 58
10  libdispatch.dylib                   0x30df18ed _dispatch_call_block_and_release + 16
11  libdispatch.dylib                   0x30deced1 _dispatch_queue_drain + 240
12  libdispatch.dylib                   0x30ded043 _dispatch_queue_invoke + 78
13  libdispatch.dylib                   0x30dec611 _dispatch_worker_thread2 + 196
14  libsystem_c.dylib                   0x34cda591 _pthread_wqthread + 264
15  libsystem_c.dylib                   0x34cdabc4 _init_cpu_capabilities + 4294967295

代码如下:

@implementation AVUtils : NSObject

+ (void) dubAudio:(NSURL*)videoUrl 
    withTrack:(NSURL*)audioUrl 
     outputTo:(NSURL*)newUrl 
    handleSuccess:(void(^)(void))successHandler 
    handleFailure:(void(^)(NSError* err))failureHandler
{
  AVURLAsset* video = [[AVURLAsset alloc]initWithURL:videoUrl options:nil];
  AVAssetTrack* videoTrack = [[video tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];
  CMTime videoDuration = video.duration;

  AVURLAsset* audio = [[AVURLAsset alloc]initWithURL:audioUrl options:nil];
  AVAssetTrack* audioTrack = [[audio tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0];
  CMTime audioDuration = audio.duration;

  CMTime newDuration = CMTimeMinimum(audioDuration, videoDuration);
  CMTimeRange newTimeRange = CMTimeRangeMake(kCMTimeZero, newDuration);

  AVMutableComposition* newComposition = [AVMutableComposition composition];
  NSError* theError;
  BOOL success;

  AVMutableCompositionTrack* newAudioTrack = [newComposition addMutableTrackWithMediaType:AVMediaTypeAudio
                                 preferredTrackID:kCMPersistentTrackID_Invalid];
  theError = nil;
  success = [newAudioTrack insertTimeRange:newTimeRange ofTrack:audioTrack atTime:kCMTimeZero error:&theError];
  if (success == NO) {
    UIAlertView* alertView = [[UIAlertView alloc] initWithTitle:@"Error adding audio track"
                          message:[theError localizedDescription]
                          delegate: nil
                          cancelButtonTitle:@"Cancel"
                          otherButtonTitles:nil];
    [alertView show];
    [alertView release];
  } else {

    AVMutableCompositionTrack* newVideoTrack = [newComposition addMutableTrackWithMediaType:AVMediaTypeVideo
                                   preferredTrackID:kCMPersistentTrackID_Invalid];
    theError = nil;
    success = [newVideoTrack insertTimeRange:newTimeRange ofTrack:videoTrack atTime:kCMTimeZero error:&theError];
    if (success == NO) {
      UIAlertView* alertView = [[UIAlertView alloc] initWithTitle:@"Error adding audio track"
                            message:[theError localizedDescription]
                            delegate: nil
                            cancelButtonTitle:@"Cancel"
                            otherButtonTitles:nil];
      [alertView show];
      [alertView release];
    } else {

      AVAssetExportSession* _assetExport = [[AVAssetExportSession alloc] initWithAsset:newComposition presetName:AVAssetExportPresetPassthrough];
      _assetExport.outputFileType = @"com.apple.quicktime-movie";
      _assetExport.outputURL = newUrl;
      _assetExport.shouldOptimizeForNetworkUse = YES;

      [_assetExport exportAsynchronouslyWithCompletionHandler:
      ^(void) {
             if (_assetExport.status == AVAssetExportSessionStatusCompleted) {
               successHandler();
             } else {
               failureHandler(_assetExport.error);
             }

             [_assetExport release];
             [video release];
             [audio release];
             [newComposition release];
           }
       ];
    }
  }
}
@end

我的理论是，我泄漏了指向 _assetExport.error 的指针，将其传递给另一个线程(我就是这样)，然后在取消引用时它无效，因为 _assetExport 正在被垃圾收集。但我验证了即使导出成功也会发生段错误，所以在本例中不是这样。

我对 Obj-C 还很陌生——任何人都可以看到我在这里所做的任何其他明显的缺陷吗？

Answer 1

看起来与完成 block 有关的内存管理是问题所在。崩溃日志表明它在释放 _assetExport 时崩溃。您绝对不应该释放 newComposition (您没有分配或保留它)。