Swift: 从 url 中检索音频文件标记列表？

Question

我只想获取音频文件中的标记列表。我认为这将是一个简单的常见任务，不会太困难。但是，我几乎找不到任何示例代码或文档，所以我最终得到了这个：

private func getMarkers(_ url: CFURL) -> AudioFileMarkerList {

  var file: AudioFileID?
  var size: UInt32 = 0
  var markers = AudioFileMarkerList()

  AudioFileOpenURL(url, .readPermission, kAudioFileWAVEType, &file)
  AudioFileGetPropertyInfo(file!, kAudioFilePropertyMarkerList, &size, nil)
  AudioFileGetProperty(file!, kAudioFilePropertyMarkerList, &size, &markers)

  return markers
}

遗憾的是，这不起作用：error: memory read failed for 0x0。

我就是想不通这个问题。我检查了 url 和大小（均有效），但始终无法检索标记。任何对此的帮助都会很棒！

编辑： 这种作品，但所有数据都是完全错误的，我无法理解单个音频文件如何具有多个 AudioFileMarkerLists 标记：

private func getMarkers(_ url: CFURL) -> [AudioFileMarkerList] {

  var file: AudioFileID?
  var size: UInt32 = 0

  AudioFileOpenURL(url, .readPermission, kAudioFileWAVEType, &file)
  AudioFileGetPropertyInfo(file!, kAudioFilePropertyMarkerList, &size, nil)

  let length = NumBytesToNumAudioFileMarkers(Int(size))
  var markers = [AudioFileMarkerList](repeating: AudioFileMarkerList(), count: length)
  AudioFileGetProperty(file!, kAudioFilePropertyMarkerList, &size, &markers)
  return markers
}

编辑 2： 根据我目前看到的大多数答案，这应该可行，但它 returns 是一个空数组：

private func getMarkers(_ url: CFURL) -> [AudioFileMarkerList] {

  var file: AudioFileID?
  var size: UInt32 = 0

  AudioFileOpenURL(url, .readPermission, kAudioFileWAVEType, &file)
  AudioFileGetPropertyInfo(file!, kAudioFilePropertyMarkerList, &size, nil)
  let length = NumBytesToNumAudioFileMarkers(Int(size))

  var markers = [AudioFileMarkerList]()
  markers.reserveCapacity(length)
  AudioFileGetProperty(file!, kAudioFilePropertyMarkerList, &size, &markers)

  return markers

}

编辑 3： 我从 Ryan 的代码中删除了一堆错误检查和有用的东西，供任何想快速尝试找出问题的人使用：

private func getMarkers(_ url: CFURL) -> [AudioFileMarker]? {

    var file: AudioFileID?
    var size: UInt32 = 0
    var markers: [AudioFileMarker] = []

    AudioFileOpenURL(url, .readPermission, kAudioFileWAVEType, &file)

    AudioFileGetPropertyInfo(file!, kAudioFilePropertyMarkerList, &size, nil)

    let length = NumBytesToNumAudioFileMarkers(Int(size))

    let data = UnsafeMutablePointer<AudioFileMarkerList>.allocate(capacity: length)

    AudioFileGetProperty(file!, kAudioFilePropertyMarkerList, &size, data)

    markers.append(data.pointee.mMarkers)

    data.deallocate(capacity: length)

    return markers
}

我只是希望 Apple 真的首先测试了 AudioFileMarkerList。

编辑 4： 感谢 Rhythmic Fistman 和 Ryan Francesconi 解决了！最终结果：

private func getMarkers(_ url: CFURL) -> [AudioFileMarker]? {

  var file: AudioFileID?
  var size: UInt32 = 0
  var markerList: [AudioFileMarker] = []

  AudioFileOpenURL(url, .readPermission, kAudioFileWAVEType, &file)

  AudioFileGetPropertyInfo(file!, kAudioFilePropertyMarkerList, &size, nil)

  let length = NumBytesToNumAudioFileMarkers(Int(size))

  let data = UnsafeMutablePointer<AudioFileMarkerList>.allocate(capacity: length)

  AudioFileGetProperty(file!, kAudioFilePropertyMarkerList, &size, data)

  let markers = UnsafeBufferPointer<AudioFileMarker>(start: &data.pointee.mMarkers, count: length)
  for marker in markers {
    markerList.append(marker)
  }

  data.deallocate(capacity: length)

  return markerList
}

Answer 1

编辑： 最简单的解决方案是使用 AudioKit 版本的 EZAudioFile.markers。请注意，这与原始 EZAudio 框架不同，因为我仅将此标记代码添加到 AudioKit 的版本中。

import AudioKit
...

if let file = EZAudioFile(url: url) {
    if let markers = file.markers as? [EZAudioFileMarker] {
        for m in markers {
            Swift.print("NAME: \(m.name) FRAME: \(m.framePosition)")
        }
    }
}

如果您真的想在Swift中尝试，它看起来像下面这样。我不是这方面的专家，但据我所知，翻译 AudioFileMarkerList struct to Swift. This may be solvable, but it seems to me it's best to just use Objective C to accomplish these calls. Here is the almost finished function in Swift. I recommend using AudioKit to accomplish what you need as I have added the marker code to EZAudioFile there. Check: https://github.com/AudioKit/AudioKit/blob/master/AudioKit/Common/Internals/EZAudio/EZAudioFile.m

时存在一些问题

但这里要记录的是 Swift 代码正在进行中！请注意，目前它被硬编码为 WAVE 文件......也许其他人可以完成这个？

class func getAudioFileMarkers(_ url: URL) -> [AudioFileMarker]? {
    Swift.print("getAudioFileMarkers() \(url)")

    var err: OSStatus = noErr
    var audioFileID: AudioFileID?

    err = AudioFileOpenURL(url as CFURL,
                           .readPermission,
                           kAudioFileWAVEType,
                           &audioFileID)

    if err != noErr {
        Swift.print("AudioFileOpenURL FAILED, Error: \(err)")
        return nil
    }

    guard audioFileID != nil else {
        return nil
    }

    Swift.print("audioFileID: \(audioFileID)")

    var outSize: UInt32 = 0
    var writable: UInt32 = 0

    err = AudioFileGetPropertyInfo(audioFileID!, kAudioFilePropertyMarkerList, &outSize, &writable)
    if err != noErr {
        Swift.print("AudioFileGetPropertyInfo kAudioFilePropertyMarkerList FAILED, Error: \(err)")
        return nil
    }

    Swift.print("outSize: \(outSize), writable: \(writable)")

    guard outSize != 0 else { return nil }

    let length = NumBytesToNumAudioFileMarkers( Int(outSize) )

    Swift.print("Found \(length) markers")

    let theData = UnsafeMutablePointer<AudioFileMarkerList>.allocate(capacity: length)

    if length == 0 {
        return nil
    }

    // pull marker list
    err = AudioFileGetProperty(audioFileID!, kAudioFilePropertyMarkerList, &outSize, theData)

    if err != noErr {
        Swift.print("AudioFileGetProperty kAudioFilePropertyMarkerList FAILED, Error: \(err)")
        return nil
    }

    let markerList: AudioFileMarkerList = theData.pointee

    Swift.print("markerList.mMarkers: \(markerList.mMarkers)")
    // this is only showing up as a single AudioFileMarker, not an array of them.
    // I DON'T KNOW WHY. It works in Obj-C. I'm obviously missing something, or there is a problem in translation

    var out = [AudioFileMarker]()

    let mirror = Mirror(reflecting: markerList.mMarkers)
    for m in mirror.children {
        Swift.print( "label: \(m.label) value: \(m.value)" )
    }

    // for now just append the first one.
    // :(
    out.append(markerList.mMarkers)

    // done with this now
    theData.deallocate(capacity: length)

    return out
}

Answer 2

看起来您需要使用 UnsafeBufferPointer 来访问可变长度数组（例如 mMarkers）。所以而不是

out.append(markerList.mMarkers)

只添加第一个元素，这样做

let markersBuffer = UnsafeBufferPointer<AudioFileMarker>(start: &data.pointee.mMarkers,
                                               count: Int(data.pointee.mNumberMarkers))

for marker in markersBuffer {
    markers.append(marker)
}

仿照this answer

Swift: 从 url 中检索音频文件标记列表？

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