Question

我正在尝试将.mov视频转换为.mp4，同时更正方向。我在下面使用的代码在使用UIImagePickerController录制视频时非常有用，但是如果从相机胶卷中选择了视频，我会收到此错误，我不明白为什么：

导出失败：操作已停止：错误 Domain = AVFoundationErrorDomain Code = -11841“Operation Stopped” UserInfo = 0x1815ca50 {NSLocalizedDescription =操作已停止， NSLocalizedFailureReason =视频无法合成。}

我先尝试将视频保存到另一个文件，但没有任何区别。

以下是我用来转换视频的代码：

- (void)convertVideoToLowQuailtyAndFixRotationWithInputURL:(NSURL*)inputURL handler:(void (^)(NSURL *outURL))handler
{
    if ([[inputURL pathExtension] isEqualToString:@"MOV"])
    {
        NSURL *outputURL = [inputURL URLByDeletingPathExtension];
        outputURL = [outputURL URLByAppendingPathExtension:@"mp4"];

        AVURLAsset *avAsset = [AVURLAsset URLAssetWithURL:inputURL options:nil];

        AVAssetTrack *sourceVideoTrack = [[avAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];
        AVAssetTrack *sourceAudioTrack = [[avAsset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0];

        AVMutableComposition* composition = [AVMutableComposition composition];

        AVMutableCompositionTrack *compositionVideoTrack = [composition addMutableTrackWithMediaType:AVMediaTypeVideo
                                                                                    preferredTrackID:kCMPersistentTrackID_Invalid];
        [compositionVideoTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, avAsset.duration)
                                       ofTrack:sourceVideoTrack
                                        atTime:kCMTimeZero error:nil];
        [compositionVideoTrack setPreferredTransform:sourceVideoTrack.preferredTransform];

        AVMutableCompositionTrack *compositionAudioTrack = [composition addMutableTrackWithMediaType:AVMediaTypeAudio
                                                                                    preferredTrackID:kCMPersistentTrackID_Invalid];
        [compositionAudioTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, avAsset.duration)
                                       ofTrack:sourceAudioTrack
                                        atTime:kCMTimeZero error:nil];

        AVMutableVideoComposition *videoComposition = [self getVideoComposition:avAsset];

        NSArray *compatiblePresets = [AVAssetExportSession exportPresetsCompatibleWithAsset:avAsset];
        if ([compatiblePresets containsObject:AVAssetExportPresetMediumQuality])
        {
            AVAssetExportSession *exportSession = [[AVAssetExportSession alloc]initWithAsset:composition presetName:AVAssetExportPresetMediumQuality];
            exportSession.outputURL = outputURL;
            exportSession.outputFileType = AVFileTypeMPEG4;
            exportSession.shouldOptimizeForNetworkUse = YES;
            exportSession.videoComposition = videoComposition;
            [exportSession exportAsynchronouslyWithCompletionHandler:^{

                switch ([exportSession status])
                {
                    case AVAssetExportSessionStatusFailed:
                        NSLog(@"Export failed: %@ : %@", [[exportSession error] localizedDescription], [exportSession error]);
                        handler(nil);

                        break;
                    case AVAssetExportSessionStatusCancelled:

                        NSLog(@"Export canceled");
                        handler(nil);

                        break;
                    default:

                        handler(outputURL);

                        break;

                }
            }];
        }

    } else {
        handler(inputURL);
    }
}

- (AVMutableVideoComposition *)getVideoComposition:(AVAsset *)asset
{
    AVAssetTrack *videoTrack = [[asset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];
    AVMutableComposition *composition = [AVMutableComposition composition];
    AVMutableVideoComposition *videoComposition = [AVMutableVideoComposition videoComposition];
    CGSize videoSize = videoTrack.naturalSize;
    BOOL isPortrait_ = [self isVideoPortrait:asset];
    if(isPortrait_) {
//        NSLog(@"video is portrait ");
        videoSize = CGSizeMake(videoSize.height, videoSize.width);
    }
    composition.naturalSize     = videoSize;
    videoComposition.renderSize = videoSize;
    videoComposition.frameDuration = CMTimeMakeWithSeconds( 1 / videoTrack.nominalFrameRate, 600);

    AVMutableCompositionTrack *compositionVideoTrack;
    compositionVideoTrack = [composition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
    [compositionVideoTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, asset.duration) ofTrack:videoTrack atTime:kCMTimeZero error:nil];
    AVMutableVideoCompositionLayerInstruction *layerInst;
    layerInst = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:videoTrack];
    [layerInst setTransform:videoTrack.preferredTransform atTime:kCMTimeZero];
    AVMutableVideoCompositionInstruction *inst = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
    inst.timeRange = CMTimeRangeMake(kCMTimeZero, asset.duration);
    inst.layerInstructions = [NSArray arrayWithObject:layerInst];
    videoComposition.instructions = [NSArray arrayWithObject:inst];
    return videoComposition;
}

Answer 1

AVFoundation Error Constant -11841表示您的视频合成无效。如果您想了解有关错误常数的更多信息，请参阅此链接： https://developer.apple.com/library/ios/documentation/AVFoundation/Reference/AVFoundation_ErrorConstants/Reference/reference.html

虽然我没有立即出现重大错误，但我可以建议以下方法来缩小您的问题来源。

首先，不要在这些调用中传递nil error参数：

[compositionVideoTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, avAsset.duration)
                                       ofTrack:sourceVideoTrack
                                        atTime:kCMTimeZero error:nil];

创建一个NSError对象并将引用传递给它，如下所示：

NSError *error = nil;
[compositionVideoTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, avAsset.duration)
                                       ofTrack:sourceVideoTrack
                                        atTime:kCMTimeZero error:&error];

检查错误以确保您的视频和音轨正确插入合成轨道。如果一切顺利，错误应为nil。

if(error)
    NSLog(@"Insertion error: %@", error);

您可能还想检查AVAsset的composable和exportable以及hasProtectedContent属性。如果这些分别不是YES，YES和NO，则可能在创建新视频文件时出现问题。

我偶尔会遇到一个问题，即在录制视频轨道的合成中使用时，创建音轨的时间范围并不像600时标。您可能希望在

中为持续时间（avAsset.duration）创建新的CMTime

CMTimeRangeMake(kCMTimeZero, avAsset.duration)

仅用于插入音轨。在新的CMTime中，使用44100的时间刻度（或音轨的采样率。）videoComposition.frameDuration同样如此。根据视频轨道的nominalFrameRate，您的时间可能无法正确显示600时间刻度。

最后，Apple提供了一个有用的工具来调试视频合成：

https://developer.apple.com/library/mac/samplecode/AVCompositionDebugViewer/Introduction/Intro.html

它可以直观地展示你的作品，你可以看到它们看起来不应该的样子。

Answer 2

尝试评论以下行并运行您的项目

exportSession.videoComposition = videoComposition;

Answer 3

你绝对应该使用AVVideoCompostion的方法isValidForAsset：timeRange：validationDelegate：它将诊断你的视频合成的任何问题。我有同样的问题，我的解决方案是使用AVMutableCompositionTrack而不是原始轨道创建layerInstruction：

layerInst = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:compositionVideoTrack];

视频来自相机胶卷时AVAssetExportSession旋转错误

3 个答案: