AVAssetWriter sometimes fails with status AVAssetWriterStatusFailed. Seems random

Question

I'm writing a MP4 video file with a AVAssetWriter using a AVAssetWriterInputPixelBufferAdaptor.

The source is a video from a UIImagePickerController, either freshly captured from the camera or from the asset library. Quality right now is UIImagePickerControllerQualityTypeMedium.

Some times the writer fails. It's status is AVAssetWriterStatusFailed and the AVAssetWriter objects error property is:

Error Domain=AVFoundationErrorDomain Code=-11800 "The operation could not be completed" 
UserInfo=0xf5d8990 {NSLocalizedFailureReason=An unknown error occurred (-536870210), 
NSUnderlyingError=0x4dd8e0 "The operation couldn’t be completed. (OSStatus error -536870210.)",
NSLocalizedDescription=The operation could not be completed

The error occurs approximately 20% of the times the code is run. It seems to fail more frequently on iPhone 4 / 4S than on iPhone 5.

It also occurs more frequently if the source video quality is higher. Using UIImagePickerControllerQualityTypeLow the error doesn't happen so often. Using UIImagePickerControllerQualityTypeHigh, the error happens a little more frequently.

I have also noticed something else: It seems to come in waves. When it fails, the following runs will often fail too, even though I delete the app and reinstall it. That leaves me wondering, whether my program leaks some memory and if that memory stays alive even if the app gets killed (is that even possible?).

Here is the code i use to render my video:

- (void)writeVideo
{
    offlineRenderingInProgress = YES;

/* --- Writer Setup --- */

    [locationQueue cancelAllOperations];

    [self stopWithoutRewinding];

    NSError *writerError = nil;

    BOOL succes;

    succes = [[NSFileManager defaultManager] removeItemAtURL:self.outputURL error:nil];

    // DLog(@"Url: %@, succes: %i, error: %@", self.outputURL, succes, fileError);

    writer = [AVAssetWriter assetWriterWithURL:self.outputURL fileType:(NSString *)kUTTypeQuickTimeMovie error:&writerError];
    //writer.shouldOptimizeForNetworkUse = NO;

    if (writerError) {
        DLog(@"Writer error: %@", writerError);
        return;
    }

    float bitsPerPixel;
    CMVideoDimensions dimensions = CMVideoFormatDescriptionGetDimensions((__bridge CMVideoFormatDescriptionRef)([readerVideoOutput.videoTracks[0] formatDescriptions][0]));
    int numPixels = dimensions.width * dimensions.height;
    int bitsPerSecond;

    // Assume that lower-than-SD resolutions are intended for streaming, and use a lower bitrate
    if ( numPixels < (640 * 480) )
        bitsPerPixel = 4.05; // This bitrate matches the quality produced by AVCaptureSessionPresetMedium or Low.
    else
        bitsPerPixel = 11.4; // This bitrate matches the quality produced by AVCaptureSessionPresetHigh.

    bitsPerSecond = numPixels * bitsPerPixel;

    NSDictionary *videoCompressionSettings = [NSDictionary dictionaryWithObjectsAndKeys:
                                          AVVideoCodecH264, AVVideoCodecKey,
                                          [NSNumber numberWithFloat:videoSize.width], AVVideoWidthKey,
                                          [NSNumber numberWithInteger:videoSize.height], AVVideoHeightKey,
                                          [NSDictionary dictionaryWithObjectsAndKeys:
                                           [NSNumber numberWithInteger:30], AVVideoMaxKeyFrameIntervalKey,
                                           nil], AVVideoCompressionPropertiesKey,
                                          nil];

    writerVideoInput = [AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeVideo outputSettings:videoCompressionSettings];
    writerVideoInput.transform =  movie.preferredTransform;
    writerVideoInput.expectsMediaDataInRealTime = YES;
    [writer addInput:writerVideoInput];

    NSDictionary *sourcePixelBufferAttributesDictionary = [NSDictionary dictionaryWithObjectsAndKeys:
                                                       [NSNumber numberWithInt:kCVPixelFormatType_32ARGB], kCVPixelBufferPixelFormatTypeKey, nil];

    writerPixelAdaptor = [AVAssetWriterInputPixelBufferAdaptor assetWriterInputPixelBufferAdaptorWithAssetWriterInput:writerVideoInput
                                                                                      sourcePixelBufferAttributes:sourcePixelBufferAttributesDictionary];
    BOOL couldStart = [writer startWriting];

    if (!couldStart) {
        DLog(@"Could not start AVAssetWriter!");
        abort = YES;
        [locationQueue cancelAllOperations];
        return;
    }

    [self configureFilters];

    CIContext *offlineRenderContext = [CIContext contextWithOptions:@{kCIContextUseSoftwareRenderer : @NO}];


    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

    if (!self.canEdit) {
        [self createVideoReaderWithAsset:movie timeRange:CMTimeRangeFromTimeToTime(kCMTimeZero, kCMTimePositiveInfinity) forOfflineRender:YES];
    } else {
        [self createVideoReaderWithAsset:movie timeRange:CMTimeRangeWithNOVideoRangeInDuration(self.thumbnailEditView.range, movie.duration) forOfflineRender:YES];
    }

    CMTime startOffset = reader.timeRange.start;

    DLog(@"startOffset: %llu", startOffset.value);

    [self.thumbnailEditView removeFromSuperview];
    //    self.thumbnailEditView = nil;

    [glLayer removeFromSuperlayer];
    glLayer = nil;

    [playerView removeFromSuperview];
    playerView = nil;

    glContext = nil;



    [writerVideoInput requestMediaDataWhenReadyOnQueue:dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0) usingBlock:^{

        @try {


        BOOL didWriteSomething = NO;

        DLog(@"Preparing to write...");

        while ([writerVideoInput isReadyForMoreMediaData]) {

            if (abort) {
                NSLog(@"Abort == YES");
                [locationQueue cancelAllOperations];
                [writerVideoInput markAsFinished];
                videoConvertCompletionBlock(NO, writer.error.localizedDescription);
            }

            if (writer.status == AVAssetWriterStatusFailed) {
                DLog(@"Writer.status: AVAssetWriterStatusFailed, error: %@", writer.error);

                [[NSUserDefaults standardUserDefaults] setObject:[NSNumber numberWithInt:1] forKey:@"QualityOverride"];
                [[NSUserDefaults standardUserDefaults] synchronize];

                abort = YES;
                [locationQueue cancelAllOperations];
                videoConvertCompletionBlock(NO, writer.error.localizedDescription);
                return;
                DLog(@"Source file exists: %i", [[NSFileManager defaultManager] fileExistsAtPath:movie.URL.relativePath]);
            }

            DLog(@"Writing started...");

            CMSampleBufferRef buffer = nil;

            if (reader.status != AVAssetReaderStatusUnknown) {

                if (reader.status == AVAssetReaderStatusReading) {
                    buffer = [readerVideoOutput copyNextSampleBuffer];
                    if (didWriteSomething == NO) {
                        DLog(@"Copying sample buffers...");
                    }
                }

                if (!buffer) {

                    [writerVideoInput markAsFinished];

                    DLog(@"Finished...");

                    CGColorSpaceRelease(colorSpace);

                    [self offlineRenderingDidFinish];


                    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

                        [writer finishWriting];
                        if (writer.error != nil) {
                            DLog(@"Error: %@", writer.error);
                        } else {
                            DLog(@"Succes!");
                        }

                        if (writer.status == AVAssetWriterStatusCompleted) {

                            videoConvertCompletionBlock(YES, nil);
                        }

                        else {
                            abort = YES;
                            videoConvertCompletionBlock(NO, writer.error.localizedDescription);
                        }

                    });


                    return;
                }

                didWriteSomething = YES;
            }
            else {

                DLog(@"Still waiting...");
                //Reader just needs a moment to get ready...
                continue;
            }

            CVPixelBufferRef pixelBuffer = CMSampleBufferGetImageBuffer(buffer);

            if (pixelBuffer == NULL) {
                DLog(@"Pixelbuffer == NULL");
                continue;
            }

            //DLog(@"Sample call back! Pixelbuffer: %lu", CVPixelBufferGetHeight(pixelBuffer));

            //NSDictionary *options = [NSDictionary dictionaryWithObject:(__bridge id)CGColorSpaceCreateDeviceRGB() forKey:kCIImageColorSpace];

            CIImage *ciimage = [CIImage imageWithCVPixelBuffer:pixelBuffer options:nil];

            CIImage *outputImage = [self filteredImageWithImage:ciimage];


            CVPixelBufferRef outPixelBuffer = NULL;
            CVReturn status;

            CFDictionaryRef empty; // empty value for attr value.
            CFMutableDictionaryRef attrs;
            empty = CFDictionaryCreate(kCFAllocatorDefault, // our empty IOSurface properties dictionary
                                       NULL,
                                       NULL,
                                       0,
                                       &kCFTypeDictionaryKeyCallBacks,
                                       &kCFTypeDictionaryValueCallBacks);

            attrs = CFDictionaryCreateMutable(kCFAllocatorDefault,
                                              1,
                                              &kCFTypeDictionaryKeyCallBacks,
                                              &kCFTypeDictionaryValueCallBacks);

            CFDictionarySetValue(attrs,
                                 kCVPixelBufferIOSurfacePropertiesKey,
                                 empty);

            CFDictionarySetValue(attrs,
                                 kCVPixelBufferCGImageCompatibilityKey,
                                 (__bridge const void *)([NSNumber numberWithBool:YES]));

            CFDictionarySetValue(attrs,
                                 kCVPixelBufferCGBitmapContextCompatibilityKey,
                                 (__bridge const void *)([NSNumber numberWithBool:YES]));


            status = CVPixelBufferCreate(kCFAllocatorDefault, ciimage.extent.size.width, ciimage.extent.size.height, kCVPixelFormatType_32BGRA, attrs, &outPixelBuffer);

            //DLog(@"Output image size: %f, %f, pixelbuffer height: %lu", outputImage.extent.size.width, outputImage.extent.size.height, CVPixelBufferGetHeight(outPixelBuffer));

            if (status != kCVReturnSuccess) {
                DLog(@"Couldn't allocate output pixelBufferRef!");
                continue;
            }

            [offlineRenderContext render:outputImage toCVPixelBuffer:outPixelBuffer bounds:outputImage.extent colorSpace:colorSpace];

            CMTime currentSourceTime = CMSampleBufferGetPresentationTimeStamp(buffer);
            CMTime currentTime = CMTimeSubtract(currentSourceTime, startOffset);
            CMTime duration = reader.timeRange.duration;
            if (CMTIME_IS_POSITIVE_INFINITY(duration)) {
                duration = movie.duration;
            }
            CMTime durationConverted = CMTimeConvertScale(duration, currentTime.timescale, kCMTimeRoundingMethod_Default);

            float durationFloat = (float)durationConverted.value;
            float progress =  ((float) currentTime.value) / durationFloat;

            //DLog(@"duration : %f, progress: %f", durationFloat, progress);

            [self updateOfflineRenderProgress:progress];

            if (pixelBuffer != NULL && writerVideoInput.readyForMoreMediaData) {
                [writerPixelAdaptor appendPixelBuffer:outPixelBuffer withPresentationTime:currentTime];
            } else {
                continue;
            }

            if (writer.status == AVAssetWriterStatusWriting) {
                DLog(@"Writer.status: AVAssetWriterStatusWriting");
            }

            CFRelease(buffer);
            CVPixelBufferRelease(outPixelBuffer);
        }

        }

        @catch (NSException *exception) {
            DLog(@"Catching exception: %@", exception);
        }

    }];

}

Answer 1

Ok, I think I solved it myself. The bad guy was this line:

[writerVideoInput requestMediaDataWhenReadyOnQueue:dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0) usingBlock:^{ ....

The global queue I was passing is a concurrent queue. This allows a new callback to be made before the previous one is finished. The asset writer is not designed to be written to from more than one thread at a time.

Creating and using a new serial queue seems to remedy the problem:

assetWriterQueue = dispatch_queue_create("AssetWriterQueue", DISPATCH_QUEUE_SERIAL);

[writerVideoInput requestMediaDataWhenReadyOnQueue:assetWriterQueue usingBlock:^{...