iOS 视频压缩

- (void)convertVideoToLowQuailtyWithInputURL:(NSURL*)inputURL
                                   outputURL:(NSURL*)outputURL
                                     handler:(void (^)(AVAssetExportSession*))handler {

    [[NSFileManager
defaultManager] removeItemAtURL:outputURL
error:nil];
   
AVURLAsset *urlAsset = [AVURLAsset
URLAssetWithURL:inputURL
options:nil];

    AVAssetExportSession *session = [[[AVAssetExportSession
alloc]
initWithAsset: urlAsset
presetName:AVAssetExportPresetMediumQuality]
autorelease];
    session.outputURL = outputURL;

    session.outputFileType =
AVFileTypeQuickTimeMovie;

    [session exportAsynchronouslyWithCompletionHandler:^(void) {
        handler(session);
    }];
}