[iOS] 視頻壓縮

- (void) lowQuailtyWithInputURL:(NSURL*)inputURL
                                   outputURL:(NSURL*)outputURL
                                     blockHandler:(void (^)(AVAssetExportSession*))handler
{
    AVURLAsset *asset = [AVURLAsset URLAssetWithURL:inputURL options:nil];
    AVAssetExportSession *session = [[AVAssetExportSession alloc] initWithAsset:asset     presetName:AVAssetExportPresetMediumQuality];
    session.outputURL = outputURL;
    session.outputFileType = AVFileTypeQuickTimeMovie;
    [session exportAsynchronouslyWithCompletionHandler:^(void)
     {
         handler(session);
     }];
}

[self lowQuailtyWithInputURL:video outputURL:output blockHandler:^(AVAssetExportSession *session)
{
     if (session.status == AVAssetExportSessionStatusCompleted)
     {
         
     }
     else
     {
         
         
     }
}];

在block裏面檢測成功，失敗，或者是取消，然後釋放session.

期間可以通過不斷的查看session的progress屬性來獲取轉換的進度。

可以設置這些壓縮質量

AVF_EXPORT NSString *const AVAssetExportPresetLowQuality        NS_AVAILABLE_IOS(4_0);
AVF_EXPORT NSString *const AVAssetExportPresetMediumQuality     NS_AVAILABLE_IOS(4_0);
AVF_EXPORT NSString *const AVAssetExportPresetHighestQuality    NS_AVAILABLE_IOS(4_0);