pause a video in AVExportSession

I have a video which has to be paused at various points in time and then made into a new video.

I use insertEmptyTimeRange in AVMutableCom开发者_C百科position to pause the video and then use AVExportSession, exportAsynchronousWithCompletionHandler to export it.

But in the completionHandler I keep getting status AVAssestExportSessionStatusFailed, error code -1800 The operation could not be completed, OS due to unknown reason, & operation could not be completed.

Any help would be great, either in the way I am pausing the video or exporting it.

thanks,

videoComposition element was being set even when it was not required, removed it to recover from the error.
Hope this can help someone. thanks.