AVAssetExportSession with and without break points

问题

I have simple video compression code in low quality conversion.I am testing my code in iphone 4 with IOS-4.2.1.The problem is when I test my code on device without break points the code failed to create video(it just a zero kb file or empty file created) but when I use breakpoint checking line by line this code slowly it will make a perfect compressed video which also runs on quicktime player in mac.After compression I make zip of this video file.

NSURL *videoURL=[[self.videourlarray objectAtIndex:i] valueForKey:UIImagePickerControllerReferenceURL];
        NSURL *outputURL = [NSURL fileURLWithPath:videoFile];

        [[NSFileManager defaultManager] removeItemAtURL:outputURL error:nil];
        AVURLAsset *asset = [AVURLAsset URLAssetWithURL:videoURL options:nil];
        AVAssetExportSession *exportSession = [[AVAssetExportSession alloc] initWithAsset:asset presetName:AVAssetExportPresetLowQuality];
        exportSession.outputURL = outputURL;
        exportSession.shouldOptimizeForNetworkUse = YES;
        exportSession.outputFileType = AVFileTypeQuickTimeMovie;
        [exportSession exportAsynchronouslyWithCompletionHandler:^(void) 
         {
             NSLog(@"Export Complete %d %@", exportSession.status, exportSession.error);
             [exportSession release];
         }];

thanx for any help...

回答1:

I think you need to make sure you're not messing with the threads.. (AVFoundation guide says that the exporter is not guaranteed to run on any particular thread).

Use a block like this.

    [exportSession exportAsynchronouslyWithCompletionHandler:^(void) 
    {
    dispatch_async(dispatch_get_main_queue(), ^{
         NSLog(@"Export Complete %d %@", exportSession.status, exportSession.error);
            });

     }];

I would personally call a delegate from the block, but I presume your simple log statement is just for this example and you already know that :)

回答2:

I had the same problem. After hours of debuging, I found out that my extension of the audio file was .M4A all uppercase. Lowercasing the letters will fix the problem

来源：https://stackoverflow.com/questions/6592218/avassetexportsession-with-and-without-break-points