我正在尝试用UIImagePickerController压缩用户摄像头拍摄的视频（不是现有的视频，而是一个动态的视频）上传到我的服务器并花费少量时间这样做，所以较小的尺寸是理想的新品质相机的重量为30-45 mb。
以下是在iOS 8中使用swift进行压缩的代码，它压缩得非常好，我从35 mb轻松到2.1 mb。
func convertVideo(inputUrl: NSURL, outputURL: NSURL)
{
//setup video writer
var videoAsset = AVURLAsset(URL: inputUrl, options: nil) as AVAsset
var videoTrack = videoAsset.tracksWithMediaType(AVMediaTypeVideo)[0] as AVAssetTrack
var videoSize = videoTrack.naturalSize
var videoWriterCompressionSettings = Dictionary(dictionaryLiteral:(AVVideoAverageBitRateKey,NSNumber(integer:960000)))
var videoWriterSettings = Dictionary(dictionaryLiteral:(AVVideoCodecKey,AVVideoCodecH264),
(AVVideoCompressionPropertiesKey,videoWriterCompressionSettings),
(AVVideoWidthKey,videoSize.width),
(AVVideoHeightKey,videoSize.height))
var videoWriterInput = AVAssetWriterInput(mediaType: AVMediaTypeVideo, outputSettings: videoWriterSettings)
videoWriterInput.expectsMediaDataInRealTime = true
videoWriterInput.transform = videoTrack.preferredTransform
var videoWriter = AVAssetWriter(URL: outputURL, fileType: AVFileTypeQuickTimeMovie, error: nil)
videoWriter.addInput(videoWriterInput)
var videoReaderSettings: [String:AnyObject] = [kCVPixelBufferPixelFormatTypeKey:kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange]
var videoReaderOutput = AVAssetReaderTrackOutput(track: videoTrack, outputSettings: videoReaderSettings)
var videoReader = AVAssetReader(asset: videoAsset, error: nil)
videoReader.addOutput(videoReaderOutput)
//setup audio writer
var audioWriterInput = AVAssetWriterInput(mediaType: AVMediaTypeAudio, outputSettings: nil)
audioWriterInput.expectsMediaDataInRealTime = false
videoWriter.addInput(audioWriterInput)
//setup audio reader
var audioTrack = videoAsset.tracksWithMediaType(AVMediaTypeAudio)[0] as AVAssetTrack
var audioReaderOutput = AVAssetReaderTrackOutput(track: audioTrack, outputSettings: nil) as AVAssetReaderOutput
var audioReader = AVAssetReader(asset: videoAsset, error: nil)
audioReader.addOutput(audioReaderOutput)
videoWriter.startWriting()
//start writing from video reader
videoReader.startReading()
videoWriter.startSessionAtSourceTime(kCMTimeZero)
//dispatch_queue_t processingQueue = dispatch_queue_create("processingQueue", nil)
var queue = dispatch_queue_create("processingQueue", nil)
videoWriterInput.requestMediaDataWhenReadyOnQueue(queue, usingBlock: { () -> Void in
println("Export starting")
while videoWriterInput.readyForMoreMediaData
{
var sampleBuffer:CMSampleBufferRef!
sampleBuffer = videoReaderOutput.copyNextSampleBuffer()
if (videoReader.status == AVAssetReaderStatus.Reading && sampleBuffer != nil)
{
videoWriterInput.appendSampleBuffer(sampleBuffer)
}
else
{
videoWriterInput.markAsFinished()
if videoReader.status == AVAssetReaderStatus.Completed
{
if audioReader.status == AVAssetReaderStatus.Reading || audioReader.status == AVAssetReaderStatus.Completed
{
}
else {
audioReader.startReading()
videoWriter.startSessionAtSourceTime(kCMTimeZero)
var queue2 = dispatch_queue_create("processingQueue2", nil)
audioWriterInput.requestMediaDataWhenReadyOnQueue(queue2, usingBlock: { () -> Void in
while audioWriterInput.readyForMoreMediaData
{
var sampleBuffer:CMSampleBufferRef!
sampleBuffer = audioReaderOutput.copyNextSampleBuffer()
println(sampleBuffer == nil)
if (audioReader.status == AVAssetReaderStatus.Reading && sampleBuffer != nil)
{
audioWriterInput.appendSampleBuffer(sampleBuffer)
}
else
{
audioWriterInput.markAsFinished()
if (audioReader.status == AVAssetReaderStatus.Completed)
{
videoWriter.finishWritingWithCompletionHandler({ () -> Void in
println("Finished writing video asset.")
self.videoUrl = outputURL
var data = NSData(contentsOfURL: outputURL)!
println("Byte Size After Compression: \(data.length / 1048576) mb")
println(videoAsset.playable)
//Networking().uploadVideo(data, fileName: "Test2")
self.dismissViewControllerAnimated(true, completion: nil)
})
break
}
}
}
})
break
}
}
}// Second if
}//first while
})// first block
// return
}
以下是调用compress方法
的UIImagePickerController的代码func imagePickerController(picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [NSObject : AnyObject])
{
// Extract the media type from selection
let type = info[UIImagePickerControllerMediaType] as String
if (type == kUTTypeMovie)
{
self.videoUrl = info[UIImagePickerControllerMediaURL] as? NSURL
var uploadUrl = NSURL.fileURLWithPath(NSTemporaryDirectory().stringByAppendingPathComponent("captured").stringByAppendingString(".mov"))
var data = NSData(contentsOfURL: self.videoUrl!)!
println("Size Before Compression: \(data.length / 1048576) mb")
self.convertVideo(self.videoUrl!, outputURL: uploadUrl!)
// Get the video from the info and set it appropriately.
/*self.dismissViewControllerAnimated(true, completion: { () -> Void in
//self.next.enabled = true
})*/
}
}
正如我上面提到的，这可以减少文件大小，但是当我恢复文件时（它仍然是.mov类型），quicktime无法播放。 Quicktime确实尝试最初转换它但在中途失败（打开文件后1-2秒）。我甚至在AVPlayerController中测试了视频文件，但它没有提供有关电影的任何信息，它只是一个播放按钮没有蚂蚁加载，没有任何长度只是“ - ”，其中时间通常在玩家。 IE是一个无法播放的损坏文件。
我确定它与写资产的设置有关，不管是视频写作还是音频写作，我都不确定。它甚至可能是资产的读取导致它腐败。我已经尝试更改变量并设置不同的键进行读写，但我没有找到正确的组合，这很糟糕，我可以压缩，但得到一个损坏的文件。我完全不确定，任何帮助都会受到赞赏。 Pleeeeeeeeease。
答案 0 :(得分：17)
想出来！ 好吧有2个问题：1个问题出在videoWriter.finishWritingWithCompletionHandler函数调用上。当这个完成块被执行时，它并不意味着视频编写器已完成写入输出URL。因此，在上传实际视频文件之前，我必须检查状态是否已完成。这是一种黑客攻击，但这就是我做的事情
videoWriter.finishWritingWithCompletionHandler({() -> Void in
while true
{
if videoWriter.status == .Completed
{
var data = NSData(contentsOfURL: outputURL)!
println("Finished: Byte Size After Compression: \(data.length / 1048576) mb")
Networking().uploadVideo(data, fileName: "Video")
self.dismissViewControllerAnimated(true, completion: nil)
break
}
}
})
我遇到的第二个问题是失败状态，这是因为我一直写在同一个临时目录中，如我的问题中UIImagePickerController didFinishSelectingMediaWithInfo方法的代码所示。所以我只使用当前日期作为目录名称，因此它将是唯一的。
var uploadUrl = NSURL.fileURLWithPath(NSTemporaryDirectory().stringByAppendingPathComponent("\(NSDate())").stringByAppendingString(".mov"))
[编辑]：更好的解决方案
好的，经过大量的实验和几个月之后，我发现了一个非常好的，更简单的解决方案，可以将视频从45 mb降低到1.42 mb，质量非常好。
以下是调用的函数，而不是原始的convertVideo函数。请注意，我必须编写自己的完成处理程序参数，该参数在异步导出完成后调用。我只是称它为处理程序。
func compressVideo(inputURL: NSURL, outputURL: NSURL, handler:(session: AVAssetExportSession)-> Void)
{
var urlAsset = AVURLAsset(URL: inputURL, options: nil)
var exportSession = AVAssetExportSession(asset: urlAsset, presetName: AVAssetExportPresetMediumQuality)
exportSession.outputURL = outputURL
exportSession.outputFileType = AVFileTypeQuickTimeMovie
exportSession.shouldOptimizeForNetworkUse = true
exportSession.exportAsynchronouslyWithCompletionHandler { () -> Void in
handler(session: exportSession)
}
}
这是uiimagepickercontrollerDidFinisPickingMediaWithInfo函数中的代码。
self.compressVideo(inputURL!, outputURL: uploadUrl!, handler: { (handler) -> Void in
if handler.status == AVAssetExportSessionStatus.Completed
{
var data = NSData(contentsOfURL: uploadUrl!)
println("File size after compression: \(Double(data!.length / 1048576)) mb")
self.picker.dismissViewControllerAnimated(true, completion: nil)
}
else if handler.status == AVAssetExportSessionStatus.Failed
{
let alert = UIAlertView(title: "Uh oh", message: " There was a problem compressing the video maybe you can try again later. Error: \(handler.error.localizedDescription)", delegate: nil, cancelButtonTitle: "Okay")
alert.show()
})
}
})
答案 1 :(得分：17)
此答案已完全重写并注释为支持 Swift 4.0 。请注意，更改dateStr和AVFileType值可让您根据尺寸和质量调整最终输出。
presetName以下是为Swift 3.0编写的原始答案：
import AVFoundation
extension ViewController: AVCaptureFileOutputRecordingDelegate {
// Delegate function has been updated
func fileOutput(_ output: AVCaptureFileOutput, didFinishRecordingTo outputFileURL: URL, from connections: [AVCaptureConnection], error: Error?) {
// This code just exists for getting the before size. You can remove it from production code
do {
let data = try Data(contentsOf: outputFileURL)
print("File size before compression: \(Double(data.count / 1048576)) mb")
} catch {
print("Error: \(error)")
}
// This line creates a generic filename based on UUID, but you may want to use your own
// The extension must match with the AVFileType enum
let path = NSTemporaryDirectory() + UUID().uuidString + ".m4v"
let outputURL = URL.init(fileURLWithPath: path)
let urlAsset = AVURLAsset(url: outputURL)
// You can change the presetName value to obtain different results
if let exportSession = AVAssetExportSession(asset: urlAsset,
presetName: AVAssetExportPresetMediumQuality) {
exportSession.outputURL = outputURL
// Changing the AVFileType enum gives you different options with
// varying size and quality. Just ensure that the file extension
// aligns with your choice
exportSession.outputFileType = AVFileType.mov
exportSession.exportAsynchronously {
switch exportSession.status {
case .unknown: break
case .waiting: break
case .exporting: break
case .completed:
// This code only exists to provide the file size after compression. Should remove this from production code
do {
let data = try Data(contentsOf: outputFileURL)
print("File size after compression: \(Double(data.count / 1048576)) mb")
} catch {
print("Error: \(error)")
}
case .failed: break
case .cancelled: break
}
}
}
}
}
答案 2 :(得分：1)
您的转换方法是异步的，但没有完成块。那么你的代码怎么知道文件什么时候准备好了？也许你在完全编写之前就使用了该文件。
转换本身看起来也很奇怪 - 音频和视频通常是并行编写的，而不是串行编写的。
你的神奇压缩率可能表明你写出的帧数比实际想象的要少。
答案 3 :(得分：0)
以下是与Swift 4.0 Compress video size before attach to an email in swift兼容的代码，您还可以跟踪视频压缩的进度