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,

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