如何减小使用 UIImagePickerController 创建的视频的文件大小? [英] How can I reduce the file size of a video created with UIImagePickerController?

问题描述

我有一个应用程序，允许用户使用 UIImagePickerController 录制视频，然后将其上传到 YouTube.问题是 UIImagePickerController 创建的视频文件很大，即使视频只有 5 秒长.例如，一个 5 秒长的视频是 16-20 兆字节.我想将视频保持在 540 或 720 质量，但我想减小文件大小.

I have an app that allows a user to record a video with UIImagePickerController and then upload it to YouTube. The problem is that the video file that UIImagePickerController creates is HUGE, even when the video is only 5 seconds long. For example, a 5 second long video is 16-20 megabytes. I want to keep the video in 540 or 720 quality, but I want to reduce the file size.

我一直在尝试使用 AVFoundation 和 AVAssetExportSession 来尝试获得更小的文件大小.我试过以下代码:

I've been experimenting with AVFoundation and AVAssetExportSession to try to get a smaller file size. I've tried the following code:

AVAsset *video = [AVAsset assetWithURL:videoURL];
AVAssetExportSession *exportSession = [AVAssetExportSession exportSessionWithAsset:video presetName:AVAssetExportPresetPassthrough];
exportSession.shouldOptimizeForNetworkUse = YES;
exportSession.outputFileType = AVFileTypeMPEG4;
exportSession.outputURL = [pathToSavedVideosDirectory URLByAppendingPathComponent:@"vid1.mp4"];
[exportSession exportAsynchronouslyWithCompletionHandler:^{
    NSLog(@"done processing video!");
}];

但是这根本没有减小文件大小.我知道我在做什么是可能的，因为在 Apple 的照片应用程序中，当您选择 在 YouTube 上分享" 时，将自动处理视频文件，使其小到可以上传.我想在我的应用程序中做同样的事情.

But this hasn't reduced the file size at all. I know what I'm doing is possible because in Apple's Photos app, when you select "share on YouTube", will automatically process the video file so its small enough to upload. I want to do the same thing in my app.

我怎样才能做到这一点?

How can I accomplish this?

推荐答案

使用 AVCaptureSession 和 AVAssetWriter 你可以设置压缩设置如下:

With AVCaptureSession and AVAssetWriter you can set the compression settings as such:

NSDictionary *settings = @{AVVideoCodecKey:AVVideoCodecH264,
                           AVVideoWidthKey:@(video_width),
                           AVVideoHeightKey:@(video_height),
                           AVVideoCompressionPropertiesKey:
                               @{AVVideoAverageBitRateKey:@(desired_bitrate),
                                 AVVideoProfileLevelKey:AVVideoProfileLevelH264Main31, /* Or whatever profile & level you wish to use */
                                 AVVideoMaxKeyFrameIntervalKey:@(desired_keyframe_interval)}};

AVAssetWriterInput* writer_input = [AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeVideo outputSettings:settings];

我想如果你一开始就坚持使用 UIImagePicker 来创建电影，你将不得不使用 AVAssetReader's copyNextSampleBuffer 和 AVAssetWriter's appendSampleBuffer 方法来进行转码.

I guess if you insist on using the UIImagePicker to create the movie in the first place, you'll have to use AVAssetReader's copyNextSampleBuffer and AVAssetWriter's appendSampleBuffer methods to do the transcode.

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