Video merging in background iOS

问题

Task: Merge flyer image into flyer video.

Cases:

Create a flyer[add emoticon image/text..etc]
Create video

Case1

Press back button[user will go to app listing of flyers screen], during this we are merging flyerSnapShoot in flyerVideo.and it works perfectly.
Going to Phone Gallery we are seeing the updated video in it.

Case2

Press iPhone Home button, I am doing things same as above but facing the following error.

FAIL = Error Domain=AVFoundationErrorDomain Code=-11800 "The operation could not be completed" UserInfo=0x17266d40 {NSLocalizedDescription=The operation could not be completed, NSUnderlyingError=0x172b3920 "The operation couldn’t be completed. (OSStatus error -16980.)", NSLocalizedFailureReason=An unknown error occurred (-16980)}

Code:

- (void)modifyVideo:(NSURL *)src destination:(NSURL *)dest crop:(CGRect)crop
              scale:(CGFloat)scale overlay:(UIImage *)image
         completion:(void (^)(NSInteger, NSError *))callback {

    // Get a pointer to the asset
    AVURLAsset* firstAsset = [AVURLAsset URLAssetWithURL:src options:nil];

    // Make an instance of avmutablecomposition so that we can edit this asset:
    AVMutableComposition* mixComposition = [AVMutableComposition composition];

    // Add tracks to this composition
    AVMutableCompositionTrack *videoTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];

    // Audio track
    AVMutableCompositionTrack *audioTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];

    // Image video is always 30 seconds. So we use that unless the background video is smaller.
    CMTime inTime = CMTimeMake( MAX_VIDEO_LENGTH * VIDEOFRAME, VIDEOFRAME );
    if ( CMTimeCompare( firstAsset.duration, inTime ) < 0 ) {
        inTime = firstAsset.duration;
    }

    // Add to the video track.
    NSArray *videos = [firstAsset tracksWithMediaType:AVMediaTypeVideo];
    CGAffineTransform transform;
    if ( videos.count > 0 ) {
        AVAssetTrack *track = [videos objectAtIndex:0];
        [videoTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, inTime) ofTrack:track atTime:kCMTimeZero error:nil];
        transform = track.preferredTransform;
        videoTrack.preferredTransform = transform;
    }

    // Add the audio track.
    NSArray *audios = [firstAsset tracksWithMediaType:AVMediaTypeAudio];
    if ( audios.count > 0 ) {
        [audioTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, inTime) ofTrack:[audios objectAtIndex:0] atTime:kCMTimeZero error:nil];
    }

    NSLog(@"Natural size: %.2f x %.2f", videoTrack.naturalSize.width, videoTrack.naturalSize.height);

    // Set the mix composition size.
    mixComposition.naturalSize = crop.size;

    // Set up the composition parameters.
    AVMutableVideoComposition *videoComposition = [AVMutableVideoComposition videoComposition];
    videoComposition.frameDuration = CMTimeMake(1, VIDEOFRAME );
    videoComposition.renderSize = crop.size;
    videoComposition.renderScale = 1.0;

    // Pass through parameters for animation.
    AVMutableVideoCompositionInstruction *passThroughInstruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
    passThroughInstruction.timeRange = CMTimeRangeMake(kCMTimeZero, inTime);

    // Layer instructions
    AVMutableVideoCompositionLayerInstruction *passThroughLayer = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:videoTrack];

    // Set the transform to maintain orientation
    if ( scale != 1.0 ) {
        CGAffineTransform scaleTransform = CGAffineTransformMakeScale( scale, scale);
        CGAffineTransform translateTransform = CGAffineTransformTranslate( CGAffineTransformIdentity,
                                                                          -crop.origin.x,
                                                                          -crop.origin.y);
        transform = CGAffineTransformConcat( transform, scaleTransform );
        transform = CGAffineTransformConcat( transform, translateTransform);
    }

    [passThroughLayer setTransform:transform atTime:kCMTimeZero];

    passThroughInstruction.layerInstructions = @[ passThroughLayer ];
    videoComposition.instructions = @[passThroughInstruction];

    // If an image is given, then put that in the animation.
    if ( image != nil ) {

        // Layer that merges the video and image
        CALayer *parentLayer = [CALayer layer];
        parentLayer.frame = CGRectMake( 0, 0, crop.size.width, crop.size.height);

        // Layer that renders the video.
        CALayer *videoLayer = [CALayer layer];
        videoLayer.frame = CGRectMake(0, 0, crop.size.width, crop.size.height );
        [parentLayer addSublayer:videoLayer];

        // Layer that renders flyerly image.
        CALayer *imageLayer = [CALayer layer];
        imageLayer.frame = CGRectMake(0, 0, crop.size.width, crop.size.height );
        imageLayer.contents = (id)image.CGImage;
        [imageLayer setMasksToBounds:YES];

        [parentLayer addSublayer:imageLayer];

        // Setup the animation tool
        videoComposition.animationTool = [AVVideoCompositionCoreAnimationTool videoCompositionCoreAnimationToolWithPostProcessingAsVideoLayer:videoLayer inLayer:parentLayer];
    }

    // Now export the movie
    AVAssetExportSession *exportSession = [[AVAssetExportSession alloc] initWithAsset:mixComposition presetName:AVAssetExportPresetHighestQuality];
    exportSession.videoComposition = videoComposition;

    // Export the URL
    exportSession.outputURL = dest;
    exportSession.outputFileType = AVFileTypeQuickTimeMovie;
    exportSession.shouldOptimizeForNetworkUse = YES;
    [exportSession exportAsynchronouslyWithCompletionHandler:^{
        callback( exportSession.status, exportSession.error );
    }];
}

I am calling this function from AppDelegate.m

- (void)applicationDidEnterBackground:(UIApplication *)application
{
    bgTask = [application beginBackgroundTaskWithName:@"MyTask" expirationHandler:^{
        // Clean up any unfinished task business by marking where you
        // stopped or ending the task outright.
        [application endBackgroundTask:bgTask];
        bgTask = UIBackgroundTaskInvalid;
    }];

    // Start the long-running task and return immediately.
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

        // Do the work associated with the task, preferably in chunks.
         [self goingToBg];

        [application endBackgroundTask:bgTask];
        bgTask = UIBackgroundTaskInvalid;
    });

    NSLog(@"backgroundTimeRemaining: %f", [[UIApplication sharedApplication] backgroundTimeRemaining]);
}

回答1:

Did alot RND on this issue, Didn't found solution for it.

Want to share few links hope it will help the stack community if they are in same problem[requirement].

Link1: AVExportSession to run in background

Quote related to question[copied from above Link1]

Sadly, since AVAssetExportSession uses the gpu to do some of it's work, it cannot run in the background if you are using an AVVideoComposition.

Link2: Starting AVAssetExportSession in the Background

Quote related to question[copied from above Link2]

You can start AVAssetExportSession in background. The only limitations in AVFoundation to performing work in the background, are using AVVideoCompositions or AVMutableVideoCompositions. AVVideoCompositions are using the GPU, and the GPU cannot be used in the background

Url(s) for background tasks:

APPLE DEV URL

RAYWENDERLICH URL

Stack question