NSURL *mediaURL = ...
AVPlayer *mainPlayer = [AVPlayer alloc] init];
AVPlayerItem playerItem = [[AVPlayerItem alloc] initWithURL:mediaUrl];
[mainPlayer replaceCurrentItemWithPlayerItem:playerItem];


GPUImageMovie *currentMovieFile  = [[GPUImageMovie alloc] initWithPlayerItem:playerItem];
[currentMovieFile addTarget:...];
[currentMovieFile startProcessing];