AVAssetExportSession send cancel export - ios

Question

I am making a video app where I create a new video using AVAssetExportSession. While the video is being created I want to give the user ability to cancel video creation. The problem I have is that I do not know how can I send a cancellation request to AVAssetExportSession as I assume it's running on the main thread. Once it starts I have no idea how can I send a stop request?
I tried this but it doesn't work
- (IBAction) startBtn
{
....
// Export
exportSession = [[AVAssetExportSession alloc] initWithAsset:[composition copy] presetName:AVAssetExportPresetHighestQuality];
[exportSession setOutputFileType:#"com.apple.quicktime-movie"];
exportSession.outputURL = outputMovieURL;
exportSession.videoComposition = mainComposition;
//NSLog(#"Went Here 7 ...");
[exportSession exportAsynchronouslyWithCompletionHandler:^{
switch ([exportSession status])
{
case AVAssetExportSessionStatusCancelled:
NSLog(#"Canceled ...");
break;
case AVAssetExportSessionStatusCompleted:
{
NSLog(#"Complete ... %#",outputURL); // moview url
break;
}
case AVAssetExportSessionStatusFailed:
{
NSLog(#"Faild=%# ...",exportSession.error);
break;
}
case AVAssetExportSessionStatusExporting:
NSLog(#"Exporting.....");
break;
}
}];
}
- (IBAction) cancelBtn
{
exportSession = nil;
}

Answer 1

You can cancel an export session by sending it the message cancelExport.
To accomplish this, you simply need to have an ivar (or property) which holds the current active export session:
#property (nonatomic, strong) AVAssetExportSession* exportSession;
Initialize the property:
- (IBAction) startBtn {
if (self.exportSession == nil) {
self.exportSession = [[AVAssetExportSession alloc] initWithAsset:[composition copy]
presetName:AVAssetExportPresetHighestQuality];
...
[self.exportSession exportAsynchronouslyWithCompletionHandler:^{
self.exportSession = nil;
....
}];
}
else {
// there is an export session already
}
}
In order to cancel the session:
- (IBAction) cancelBtn
{
[self.exportSession cancelExport];
self.exportSession = nil;
}
Hint: For a better user experience, you should disable/enable "Cancel" and "Start Export" buttons accordingly.