AVAssetExportSession exportAsynchronouslyWithCompletionHandler not work sometimes - ios

Question

I want to export and compress a video from iPod-Library,but the "exportAsynchronouslyWithCompletionHandler" can work correctly for some video,and not work for some video.it's not work and no throw exception.
But it is strange that if I comment out the method "setVideoComposition:",the "exportAsynchronouslyWithCompletionHandler" can work normally.
Here is my code:
AVAsset *_videoAsset = [AVAsset assetWithURL:[NSURL URLWithString:filmElementModel.alassetUrl]];
CMTime assetTime = [_videoAsset duration];
AVAssetTrack *avAssetTrack = [[_videoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];
Float64 duration = CMTimeGetSeconds(assetTime);
AVMutableComposition *avMutableComposition = [AVMutableComposition composition];
AVMutableCompositionTrack *avMutableCompositionTrack = [avMutableComposition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
NSError *error = nil;
[avMutableCompositionTrack insertTimeRange:CMTimeRangeMake(CMTimeMakeWithSeconds(0.0f, 30), CMTimeMakeWithSeconds(duration>8.0f?8.0f:duration, 30))
ofTrack:avAssetTrack
atTime:kCMTimeZero
error:&error];
AVMutableVideoComposition *avMutableVideoComposition = [AVMutableVideoComposition videoComposition];
avMutableVideoComposition.frameDuration = CMTimeMake(1, 30);
AVMutableVideoCompositionLayerInstruction *layerInstruciton = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:avMutableComposition.tracks[0]];
[layerInstruciton setTransform:[[[_videoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0] preferredTransform] atTime:kCMTimeZero];
[layerInstruciton setOpacity:0.0f atTime:[_videoAsset duration]];
AVMutableVideoCompositionInstruction *avMutableVideoCompositionInstruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
[avMutableVideoCompositionInstruction setTimeRange:CMTimeRangeMake(kCMTimeZero, [avMutableComposition duration])];
avMutableVideoCompositionInstruction.layerInstructions = [NSArray arrayWithObject:layerInstruciton];
if (avAssetTrack.preferredTransform.a) {
NSLog(#"横向");
avMutableVideoComposition.renderSize = CGSizeMake(avAssetTrack.naturalSize.width, avAssetTrack.naturalSize.height);
}else
{
avMutableVideoComposition.renderSize = CGSizeMake(avAssetTrack.naturalSize.height, avAssetTrack.naturalSize.width);
}
avMutableVideoComposition.instructions = [NSArray arrayWithObject:avMutableVideoCompositionInstruction];
// the url for save video
NSString *outUrlString = ITTPathForBabyShotResource([NSString stringWithFormat:#"%#/%#.mp4",DATA_ENV.userModel.userId,filmElementModel.filmElementId]);
NSFileManager *fm = [[NSFileManager alloc] init];
if ([fm fileExistsAtPath:outUrlString]) {
NSLog(#"video is have. then delete that");
if ([fm removeItemAtPath:outUrlString error:&error]) {
NSLog(#"delete is ok");
}else {
NSLog(#"delete is no error = %#",error.description);
}
}
CGSize renderSize = CGSizeMake(1280, 720);
if (MIN(avAssetTrack.naturalSize.width, avAssetTrack.naturalSize.height)<720) {
renderSize =avAssetTrack.naturalSize;
}
long long fileLimite =renderSize.width*renderSize.height*(duration>8.0f?8.0f:duration)/2;
_avAssetExportSession = [[AVAssetExportSession alloc] initWithAsset:avMutableComposition presetName:AVAssetExportPreset1280x720];
[_avAssetExportSession setVideoComposition:avMutableVideoComposition];
[_avAssetExportSession setOutputURL:[NSURL fileURLWithPath:outUrlString]];
[_avAssetExportSession setOutputFileType:AVFileTypeQuickTimeMovie];
[_avAssetExportSession setFileLengthLimit: fileLimite];
[_avAssetExportSession setShouldOptimizeForNetworkUse:YES];
[_avAssetExportSession exportAsynchronouslyWithCompletionHandler:^(void){
switch (_avAssetExportSession.status) {
case AVAssetExportSessionStatusFailed:
{
}
break;
case AVAssetExportSessionStatusCompleted:
{
}
break;
case AVAssetExportSessionStatusCancelled:
NSLog(#"export cancelled");
break;
case AVAssetExportSessionStatusExporting:
NSLog(#"AVAssetExportSessionStatusExporting");
break;
case AVAssetExportSessionStatusWaiting:
NSLog(#"AVAssetExportSessionStatusWaiting");
break;
}
}];
if (_avAssetExportSession.status != AVAssetExportSessionStatusCompleted){
NSLog(#"Retry export");
}

Answer 1

I solved this problem!
[avMutableCompositionTrack insertTimeRange:CMTimeRangeMake(CMTimeMakeWithSeconds(0.0f, 30), CMTimeMakeWithSeconds(duration>8.0f?8.0f:duration, 30))
ofTrack:avAssetTrack
atTime:kCMTimeZero
error:&error];
I replace the CMTimeRangeMake(CMTimeMakeWithSeconds(0.0f, 30) with CMTimeRangeMake(CMTimeMakeWithSeconds(0.1f, 30).
But I don't know why it can Work properly。