如何在iOS Swift中为CMSampleBufferGetFormatDescription创建anAudioSampleBuffer [英] How to create a anAudioSampleBuffer for CMSampleBufferGetFormatDescription in iOS Swift
问题描述
我一直在研究iOS Swift中的视频压缩，并遵循这 SO的回答.在我将这段代码的文件格式更改为 .mp4
I have been working on video compression in iOS Swift, and following this SO's answer. It is working fine until I change this piece of code's file format to .mp4
let videoWriter = try! AVAssetWriter(outputURL: outputURL as URL, fileType: AVFileType.mov)
出于某些原因，我需要使用 .mp4 文件格式的输出.因此，当我这样做时，它会使应用程序崩溃.并给了我这个错误，
There are reasons that I need the output in .mp4 file format. So when I do that it crashes the app. And gives me this error,
2020-04-27 18:20:52.573614+0500 BrightCaster[7847:1513728] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[AVAssetWriter addInput:] In order to perform passthrough to file type public.mpeg-4, please provide a format hint in the AVAssetWriterInput initializer'
*** First throw call stack:
(0x1b331d5f0 0x1b303fbcc 0x1bd53b2b0 0x102383c0c 0x102382164 0x1021897cc 0x1b6ca73bc 0x1b6caba7c 0x1b6daec94 0x1b7835080 0x1b7834d30 0x1e9d077b4 0x1b786a764 0x1b783eb68 0x1b783f070 0x1e9d468f4 0x1b783f1c0 0x1e9d468f4 0x1b9e21d9c 0x105173730 0x105181710 0x1b329b748 0x1b329661c 0x1b3295c34 0x1bd3df38c 0x1b73c822c 0x10230f8a0 0x1b311d800)
libc++abi.dylib: terminating with uncaught exception of type NSException
因此，我在SO上进行搜索，发现了与我的问题有关的此问题. 但是现在的问题是，当我尝试将其 answer 添加到我的函数中时，它给我错误 anAudioSampleBuffer未定义.由于我是音频/视频领域的新手，所以我无法理解为什么它给了我这个.以及如何解决这个问题. 我在函数中添加的答案中的代码如下.
So I searched on SO and found this question relevant to my problem. but now the issue is when I try to add its answer to my function it gives me error anAudioSampleBuffer not defined. As I am totally new to audio/video domain, I am unable to understand why it is giving me this. And how to resolve this. The piece of code from answer that I am adding with my function is below.
//setup audio writer
//let formatDesc = CMSampleBufferGetFormatDescription(anAudioSampleBuffer)
//let audioWriterInput = AVAssetWriterInput(mediaType: AVMediaType.audio, outputSettings: nil, sourceFormatHint: formatDesc)
let audioWriterInput = AVAssetWriterInput(mediaType: AVMediaType.audio, outputSettings: nil)
audioWriterInput.expectsMediaDataInRealTime = false
videoWriter.add(audioWriterInput)
被注释的部分不起作用.任何帮助将不胜感激.
The commented part is not working. Any help would be appreciated Thanks.
以下是用于转换的整个功能
Whole function for conversion is following
func convertVideoToLowQuailtyWithInputURL(inputURL: URL, outputURL: URL, completion: @escaping (Bool , _ url: String) -> Void) {
let videoAsset = AVURLAsset(url: inputURL as URL, options: nil)
let videoTrack = videoAsset.tracks(withMediaType: AVMediaType.video)[0]
let videoSize = videoTrack.naturalSize
let videoWriterCompressionSettings = [
AVVideoAverageBitRateKey : Int(125000)
]
let videoWriterSettings:[String : AnyObject] = [
AVVideoCodecKey : AVVideoCodecH264 as AnyObject,
AVVideoCompressionPropertiesKey : videoWriterCompressionSettings as AnyObject,
AVVideoWidthKey : Int(videoSize.width) as AnyObject,
AVVideoHeightKey : Int(videoSize.height) as AnyObject
]
let videoWriterInput = AVAssetWriterInput(mediaType: AVMediaType.video, outputSettings: videoWriterSettings)
videoWriterInput.expectsMediaDataInRealTime = true
videoWriterInput.transform = videoTrack.preferredTransform
let videoWriter = try! AVAssetWriter(outputURL: outputURL as URL, fileType: AVFileType.mov) // for now its converting in .mov I THINK SO.
videoWriter.add(videoWriterInput)
//setup video reader
let videoReaderSettings:[String : AnyObject] = [
kCVPixelBufferPixelFormatTypeKey as String: Int(kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange) as AnyObject
]
let videoReaderOutput = AVAssetReaderTrackOutput(track: videoTrack, outputSettings: videoReaderSettings)
var videoReader: AVAssetReader!
do{
videoReader = try AVAssetReader(asset: videoAsset)
}
catch {
print("video reader error: \(error)")
completion(false, "")
}
videoReader.add(videoReaderOutput)
//setup audio writer
//let formatDesc = CMSampleBufferGetFormatDescription(anAudioSampleBuffer) // this is giving me error here of un initilize, which I didn't I know.
//let audioWriterInput = AVAssetWriterInput(mediaType: AVMediaType.audio, outputSettings: nil, sourceFormatHint: formatDesc)
let audioWriterInput = AVAssetWriterInput(mediaType: AVMediaType.audio, outputSettings: nil)
audioWriterInput.expectsMediaDataInRealTime = false
videoWriter.add(audioWriterInput)
//setup audio reader
let audioTrack = videoAsset.tracks(withMediaType: AVMediaType.audio)[0]
let audioReaderOutput = AVAssetReaderTrackOutput(track: audioTrack, outputSettings: nil)
let audioReader = try! AVAssetReader(asset: videoAsset)
audioReader.add(audioReaderOutput)
videoWriter.startWriting()
//start writing from video reader
videoReader.startReading()
videoWriter.startSession(atSourceTime: CMTime.zero)
let processingQueue = DispatchQueue(label: "processingQueue1")
videoWriterInput.requestMediaDataWhenReady(on: processingQueue, using: {() -> Void in
while videoWriterInput.isReadyForMoreMediaData {
let sampleBuffer:CMSampleBuffer? = videoReaderOutput.copyNextSampleBuffer();
if videoReader.status == .reading && sampleBuffer != nil {
videoWriterInput.append(sampleBuffer!)
}
else {
videoWriterInput.markAsFinished()
if videoReader.status == .completed {
//start writing from audio reader
audioReader.startReading()
videoWriter.startSession(atSourceTime: CMTime.zero)
let processingQueue = DispatchQueue(label: "processingQueue2")
audioWriterInput.requestMediaDataWhenReady(on: processingQueue, using: {() -> Void in
while audioWriterInput.isReadyForMoreMediaData {
let sampleBuffer:CMSampleBuffer? = audioReaderOutput.copyNextSampleBuffer()
if audioReader.status == .reading && sampleBuffer != nil {
audioWriterInput.append(sampleBuffer!)
}
else {
audioWriterInput.markAsFinished()
if audioReader.status == .completed {
videoWriter.finishWriting(completionHandler: {() -> Void in
completion(true, "\(videoWriter.outputURL)")
})
}
}
}
})
}
}
}
})
}
推荐答案
您可以将mp4输出为mp4，通过提供格式提示来传递音频(无转码)，如下所示:
You can output as mp4, passing audio through (no transcode) by providing that format hint like so:
let audioTrack = videoAsset.tracks(withMediaType: AVMediaType.audio)[0]
let audioWriterInput = AVAssetWriterInput(mediaType: AVMediaType.audio, outputSettings: nil, sourceFormatHint: audioTrack.formatDescriptions[0] as! CMFormatDescription)
请注意audioTrack定义的新位置.
我想苹果的.mov和.mp4实现都需要知道压缩的音频格式才能写入文件，但是我想.mov可以在初始化后推断该信息，而.mp4不是.也许是另一个AVFoundation Surprise!.
I imagine both of Apple's .mov and .mp4 implementations need to know the the compressed audio format to write the file, but I guess .mov is ok with inferring that information after initialisation, where .mp4 is not. Maybe it's another AVFoundation Surprise!.
在您的情况下，我看到重新编写代码以从第一个样本缓冲区中获取音频格式会很麻烦，但是后来我想起了从输入音频轨道中可以使用的格式.
In your case I saw that it would be tiresome to rework the code to get the audio format from the first sample buffer, but then I remembered that the format is available from the input audio track.
这篇关于如何在iOS Swift中为CMSampleBufferGetFormatDescription创建anAudioSampleBuffer的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
