Error Domain=AVFoundationErrorDomain Code=-11821 "Cannot Decode" - ios

Question

There's a strange behaviour I've found when trying to merge videos with AVFoundation. I'm pretty sure that I've made a mistake somewhere but I'm too blind to see it. My goal is just to merge 4 videos (later there will be crossfade transition between them).
Everytime I'm trying to export video I get this error:
Error Domain=AVFoundationErrorDomain Code=-11821 "Cannot Decode" UserInfo=0x7fd94073cc30 {NSLocalizedDescription=Cannot Decode, NSLocalizedFailureReason=The media data could not be decoded. It may be damaged.}
The funniest thing is that if I don't provide AVAssetExportSession with AVMutableVideoComposition, then everything works fine! I can't understand what I'm doing wrong. The source videos are downloaded from youtube and have .mp4 extension. I can play them with MPMoviePlayerController. While checking the source code, please, look carefully at AVMutableVideoComposition.
I was testing this code in Xcode 6.0.1 on iOS simulator.
#import "VideoStitcher.h"
#import <UIKit/UIKit.h>
#import <AVFoundation/AVFoundation.h>
#import <AssetsLibrary/AssetsLibrary.h>
#implementation VideoStitcher
{
VideoStitcherCompletionBlock _completionBlock;
AVMutableComposition *_composition;
AVMutableVideoComposition *_videoComposition;
}
- (instancetype)init
{
self = [super init];
if (self)
{
_composition = [AVMutableComposition composition];
_videoComposition = [AVMutableVideoComposition videoComposition];
}
return self;
}
- (void)compileVideoWithAssets:(NSArray *)assets completion:(VideoStitcherCompletionBlock)completion
{
_completionBlock = [completion copy];
if (assets == nil || assets.count < 2)
{
// We need at least two video to make a stitch, right?
NSAssert(NO, #"VideoStitcher: assets parameter is nil or has not enough items in it");
}
else
{
[self composeAssets:assets];
if (_composition != nil) // if stitching went good and no errors were found
[self exportComposition];
}
}
- (void)composeAssets:(NSArray *)assets
{
AVMutableCompositionTrack *compositionVideoTrack = [_composition addMutableTrackWithMediaType:AVMediaTypeVideo
preferredTrackID:kCMPersistentTrackID_Invalid];
NSError *compositionError = nil;
CMTime currentTime = kCMTimeZero;
AVAsset *asset = nil;
for (int i = (int)assets.count - 1; i >= 0; i--) //For some reason videos are compiled in reverse order. Find the bug later. 06.10.14
{
asset = assets[i];
AVAssetTrack *assetVideoTrack = [[asset tracksWithMediaType:AVMediaTypeVideo] firstObject];
BOOL success = [compositionVideoTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, assetVideoTrack.timeRange.duration)
ofTrack:assetVideoTrack
atTime:currentTime
error:&compositionError];
if (success)
{
CMTimeAdd(currentTime, asset.duration);
}
else
{
NSLog(#"VideoStitcher: something went wrong during inserting time range in composition");
if (compositionError != nil)
{
NSLog(#"%#", compositionError);
_completionBlock(nil, compositionError);
_composition = nil;
return;
}
}
}
AVMutableVideoCompositionInstruction *videoCompositionInstruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
videoCompositionInstruction.timeRange = CMTimeRangeMake(kCMTimeZero, _composition.duration);
videoCompositionInstruction.backgroundColor = [[UIColor redColor] CGColor];
_videoComposition.instructions = #[videoCompositionInstruction];
_videoComposition.renderSize = [self calculateOptimalRenderSizeFromAssets:assets];
_videoComposition.frameDuration = CMTimeMake(1, 600);
}
- (void)exportComposition
{
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *myPathDocs = [documentsDirectory stringByAppendingPathComponent:#"testVideo.mov"];
NSURL *url = [NSURL fileURLWithPath:myPathDocs];
NSString *filePath = [url path];
NSFileManager *fileManager = [NSFileManager defaultManager];
if ([fileManager fileExistsAtPath:filePath]) {
NSError *error;
if ([fileManager removeItemAtPath:filePath error:&error] == NO) {
NSLog(#"removeItemAtPath %# error:%#", filePath, error);
}
}
AVAssetExportSession *exporter = [[AVAssetExportSession alloc] initWithAsset:_composition
presetName:AVAssetExportPreset1280x720];
exporter.outputURL = url;
exporter.outputFileType = AVFileTypeQuickTimeMovie;
exporter.shouldOptimizeForNetworkUse = YES;
exporter.videoComposition = _videoComposition;
[exporter exportAsynchronouslyWithCompletionHandler:^{
[self exportDidFinish:exporter];
}];
}
- (void)exportDidFinish:(AVAssetExportSession*)session
{
NSLog(#"%li", session.status);
if (session.status == AVAssetExportSessionStatusCompleted)
{
NSURL *outputURL = session.outputURL;
// time to call delegate methods, but for testing purposes we save the video in 'photos' app
ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];
if ([library videoAtPathIsCompatibleWithSavedPhotosAlbum:outputURL])
{
[library writeVideoAtPathToSavedPhotosAlbum:outputURL completionBlock:^(NSURL *assetURL, NSError *error){
if (error == nil)
{
NSLog(#"successfully saved video");
}
else
{
NSLog(#"saving video failed.\n%#", error);
}
}];
}
}
else if (session.status == AVAssetExportSessionStatusFailed)
{
NSLog(#"VideoStitcher: exporting failed.\n%#", session.error);
}
}
- (CGSize)calculateOptimalRenderSizeFromAssets:(NSArray *)assets
{
AVAsset *firstAsset = assets[0];
AVAssetTrack *firstAssetVideoTrack = [[firstAsset tracksWithMediaType:AVMediaTypeVideo] firstObject];
CGFloat maxWidth = firstAssetVideoTrack.naturalSize.height;
CGFloat maxHeight = firstAssetVideoTrack.naturalSize.width;
for (AVAsset *asset in assets)
{
AVAssetTrack *assetVideoTrack = [[asset tracksWithMediaType:AVMediaTypeVideo] firstObject];
if (assetVideoTrack.naturalSize.width > maxWidth)
maxWidth = assetVideoTrack.naturalSize.width;
if (assetVideoTrack.naturalSize.height > maxHeight)
maxHeight = assetVideoTrack.naturalSize.height;
}
return CGSizeMake(maxWidth, maxHeight);
}
#end
Thank you for your attention. I am really tired, I've been trying to find the bug for four hours straight. I'll go to sleep now.

Answer 1

I've finally found the solution. The description of error lead me in the wrong direction: "Cannot Decode. The media data could not be decoded. It may be damaged.". From this description you may think that there is something wrong with your video files. I've spent 5 hours experimenting with formats, debugging and etc.
Well, THE ANSWER IS COMPLETELY DIFFERENT!
My mistake was that I forgot that CMTimeADD() returns value. I thought that it changes the value of its first argument, and in the code you can see this:
CMTime currentTime = kCMTimeZero;
for (int i = (int)assets.count - 1; i >= 0; i--)
{
CMTimeAdd(currentTime, asset.duration); //HERE!! I don't actually increment the value! currentTime is always kCMTimeZero
}
videoCompositionInstruction.timeRange = CMTimeRangeMake(kCMTimeZero, _composition.duration); // And that's where everything breaks!
The lesson that I've learned: When working with AVFoundation always check your time values! It's very important, otherwise you'll get a lot of bugs.

Answer 2

Error:-
domain: "AVFoundationErrorDomain" - code: 18446744073709539816
Solution:- [Swift 5.5]
Stop running mutiple av player in back ground thread.