使用AVAssetWriter

时间：2015-11-24 21:02:44

标签： ios swift avfoundation avassetwriter

我正在尝试录制音频片段并重新组合它们而不会产生音频差距。

最终的目标是也有视频，但我发现音频本身与ffmpeg -f concat -i list.txt -c copy out.mp4

结合后会产生差距

如果我将音频放在HLS播放列表中，也有间隙，所以我认为这不是ffmpeg独有的。

这个想法是样本连续进入，我的控制器将样本路由到正确的AVAssetWriter。如何消除音频中的差距？

import Foundation
import UIKit
import AVFoundation

class StreamController: UIViewController, AVCaptureAudioDataOutputSampleBufferDelegate, AVCaptureVideoDataOutputSampleBufferDelegate {
    var closingAudioInput: AVAssetWriterInput?
    var closingAssetWriter: AVAssetWriter?

    var currentAudioInput: AVAssetWriterInput?
    var currentAssetWriter: AVAssetWriter?

    var nextAudioInput: AVAssetWriterInput?
    var nextAssetWriter: AVAssetWriter?

    var videoHelper: VideoHelper?

    var startTime: NSTimeInterval = 0
    let closeAssetQueue: dispatch_queue_t = dispatch_queue_create("closeAssetQueue", nil);

    override func viewDidLoad() {
        super.viewDidLoad()
        startTime = NSDate().timeIntervalSince1970
        createSegmentWriter()
        videoHelper = VideoHelper()
        videoHelper!.delegate = self
        videoHelper!.startSession()
        NSTimer.scheduledTimerWithTimeInterval(1, target: self, selector: "createSegmentWriter", userInfo: nil, repeats: true)
    }

    func createSegmentWriter() {
        print("Creating segment writer at t=\(NSDate().timeIntervalSince1970 - self.startTime)")
        let outputPath = OutputFileNameHelper.instance.pathForOutput()
        OutputFileNameHelper.instance.incrementSegmentIndex()
        try? NSFileManager.defaultManager().removeItemAtPath(outputPath)
        nextAssetWriter = try! AVAssetWriter(URL: NSURL(fileURLWithPath: outputPath), fileType: AVFileTypeMPEG4)
        nextAssetWriter!.shouldOptimizeForNetworkUse = true

        let audioSettings: [String:AnyObject] = EncodingSettings.AUDIO
        nextAudioInput = AVAssetWriterInput(mediaType: AVMediaTypeAudio, outputSettings: audioSettings)
        nextAudioInput!.expectsMediaDataInRealTime = true
        nextAssetWriter?.addInput(nextAudioInput!)

        nextAssetWriter!.startWriting()
    }

    func closeWriterIfNecessary() {
        if closing && audioFinished {
            closing = false
            audioFinished = false
            let outputFile = closingAssetWriter?.outputURL.pathComponents?.last
            closingAssetWriter?.finishWritingWithCompletionHandler() {
                let delta = NSDate().timeIntervalSince1970 - self.startTime
                print("segment \(outputFile!) finished at t=\(delta)")
            }
            self.closingAudioInput = nil
            self.closingAssetWriter = nil
        }
    }

    var audioFinished = false
    var closing = false

    func captureOutput(captureOutput: AVCaptureOutput!, didOutputSampleBuffer sampleBuffer: CMSampleBufferRef, fromConnection connection: AVCaptureConnection!) {
        if let nextWriter = nextAssetWriter {
            if nextWriter.status.rawValue != 0 {
                if (currentAssetWriter != nil) {
                    closing = true
                }

                var sampleTiming: CMSampleTimingInfo = kCMTimingInfoInvalid
                CMSampleBufferGetSampleTimingInfo(sampleBuffer, 0, &sampleTiming)

                print("Switching asset writers at t=\(NSDate().timeIntervalSince1970 - self.startTime)")
                closingAssetWriter = currentAssetWriter
                closingAudioInput = currentAudioInput

                currentAssetWriter = nextAssetWriter
                currentAudioInput = nextAudioInput

                nextAssetWriter = nil
                nextAudioInput = nil

                currentAssetWriter?.startSessionAtSourceTime(sampleTiming.presentationTimeStamp)
            }
        }

        if let _ = captureOutput as? AVCaptureVideoDataOutput {
        } else if let _ = captureOutput as? AVCaptureAudioDataOutput {
            captureAudioSample(sampleBuffer)
        }

        dispatch_async(closeAssetQueue) {
            self.closeWriterIfNecessary()
        }
    }

    func printTimingInfo(sampleBuffer: CMSampleBufferRef, prefix: String) {
        var sampleTiming: CMSampleTimingInfo = kCMTimingInfoInvalid
        CMSampleBufferGetSampleTimingInfo(sampleBuffer, 0, &sampleTiming)
        let presentationTime = Double(sampleTiming.presentationTimeStamp.value) / Double(sampleTiming.presentationTimeStamp.timescale)
        print("\(prefix):\(presentationTime)")
    }

    func captureAudioSample(sampleBuffer: CMSampleBufferRef) {
        printTimingInfo(sampleBuffer, prefix: "A")
        if (closing && !audioFinished) {
            if closingAudioInput?.readyForMoreMediaData == true {
                closingAudioInput?.appendSampleBuffer(sampleBuffer)
            }
            closingAudioInput?.markAsFinished()
            audioFinished = true
        } else {
            if currentAudioInput?.readyForMoreMediaData == true {
                currentAudioInput?.appendSampleBuffer(sampleBuffer)
            }
        }
    }
}

2 个答案:

答案 0 :(得分：5)

对于像AAC这样的数据包格式，您在开始时有静音启动帧（a.k.a编码器延迟），在结尾处有剩余帧（当您的音频长度不是数据包大小的倍数时）。在你的情况下，它们在每个文件的开头是2112。启动和剩余帧会破坏连接文件而不对其进行转码的可能性，因此您无法真正责备<?php $orderProv = 1; //$QueryProvinces = Query Province; foreach ($QueryProvinces as $QueryProvince) { ?> <tr> <td> <?php echo $orderProv; ?></td> <td> <?php echo $QueryProvince->nameProv; ?></td> <?php //$QueryDistricts = Query District; foreach ($QueryDistricts as $QueryDistrict ) { ?> <td> <?php echo $QueryDistrict ->nameDist; ?></td> <?php } ?> </tr> <?php } ?> 无法生成无缝输出。

我不知道这会给你留下什么视频 - 显然音频会同步到视频，即使有启动帧也是如此。

这完全取决于你打算如何连接最终的音频（最终是视频）。如果您使用ffmpeg -c copy自行执行此操作，则可以使用

检测并计算启动/余数帧 
AVFoundation

作为短期解决方案，您可以切换到非＆＃34;分组化的＆＃34;获得无间隙，可连接（使用ffmpeg）文件。

e.g。

CMGetAttachment(buffer, kCMSampleBufferAttachmentKey_TrimDurationAtStart, NULL) CMGetAttachment(audioBuffer, kCMSampleBufferAttachmentKey_TrimDurationAtEnd, NULL) ，AVFormatIDKey: kAudioFormatAppleIMA4，后缀＆＃34; .aifc＆＃34;要么 fileType: AVFileTypeAIFC，AVFormatIDKey: kAudioFormatLinearPCM，后缀＆＃34; .wav＆＃34;

P.S。你可以看到启动＆amp;使用无处不在的fileType: AVFileTypeWAVE工具的剩余帧和数据包大小。

afinfo
  

数据格式：2 ch，44100 Hz，＆＃39; aac＆＃39; （0x00000000）0比特/信道，0字节/分组，1024帧/分组，0字节/帧
  ...
  音频39596有效帧+ 2112启动+ 276余数= 41984
  ......

答案 1 :(得分：0)

不确定这是否对您有所帮助，但如果您有一堆MP4，则可以使用此代码将它们组合起来：

func mergeAudioFiles(audioFileUrls: NSArray, callback: (url: NSURL?, error: NSError?)->()) {

    // Create the audio composition
    let composition = AVMutableComposition()

    // Merge
    for (var i = 0; i < audioFileUrls.count; i++) {

        let compositionAudioTrack :AVMutableCompositionTrack = composition.addMutableTrackWithMediaType(AVMediaTypeAudio, preferredTrackID: CMPersistentTrackID())

        let asset = AVURLAsset(URL: audioFileUrls[i] as! NSURL)

        let track = asset.tracksWithMediaType(AVMediaTypeAudio)[0]

        let timeRange = CMTimeRange(start: CMTimeMake(0, 600), duration: track.timeRange.duration)

        try! compositionAudioTrack.insertTimeRange(timeRange, ofTrack: track, atTime: composition.duration)
    }

    // Create output url
    let format = NSDateFormatter()
    format.dateFormat="yyyy-MM-dd-HH-mm-ss"
    let currentFileName = "recording-\(format.stringFromDate(NSDate()))-merge.m4a"
    print(currentFileName)

    let documentsDirectory = NSFileManager.defaultManager().URLsForDirectory(.DocumentDirectory, inDomains: .UserDomainMask)[0]
    let outputUrl = documentsDirectory.URLByAppendingPathComponent(currentFileName)
    print(outputUrl.absoluteString)

    // Export it
    let assetExport = AVAssetExportSession(asset: composition, presetName: AVAssetExportPresetAppleM4A)
    assetExport?.outputFileType = AVFileTypeAppleM4A
    assetExport?.outputURL = outputUrl

    assetExport?.exportAsynchronouslyWithCompletionHandler({ () -> Void in
        switch assetExport!.status {
            case AVAssetExportSessionStatus.Failed:
                callback(url: nil, error: assetExport?.error)
            default:
                callback(url: assetExport?.outputURL, error: nil)
        }
    })

}
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