Swift: Retrieve audio file marker list from url? - ios

Question

I just want to get a list of the markers in an audio file. I thought this would be an easy common task that wouldn't be too difficult. However, I can barely find any example code or documentation, so I ended up with this:
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
}
Sadly, this doesn't work: error: memory read failed for 0x0.
I just can't figure out the problem. I checked the url and the size (which are both valid), but it always fails to retrieve the markers. Any help with this would be fantastic!
EDIT:
This sort of works, but all the data is completely wrong, and I can't understand how a single audio file can have multiple AudioFileMarkerLists of markers:
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
}
EDIT 2: According to most answers I've seen so far, this should work, but it returns an empty array:
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
}
EDIT 3:
I got rid of a bunch of error checking and useful stuff from Ryan's code for anyone wanting to quickly try and find the problem:
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
}
I just hope Apple actually tested AudioFileMarkerList in the first place.
EDIT 4:
SOLVED thanks to Rhythmic Fistman and Ryan Francesconi! Final result:
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

Looks like you need to use UnsafeBufferPointer to access variable length arrays (like mMarkers). So instead of
out.append(markerList.mMarkers)
which only adds the first element, do this
let markersBuffer = UnsafeBufferPointer<AudioFileMarker>(start: &data.pointee.mMarkers,
count: Int(data.pointee.mNumberMarkers))
for marker in markersBuffer {
markers.append(marker)
}
Modeled on this answer

Answer 2

EDIT: Simplest solution is to use AudioKit's version of EZAudioFile.markers. Note this is not the same as the original EZAudio framework as I had added this marker code to AudioKit's version only.
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)")
}
}
}
If you REALLY want to try in Swift, it would look something like the below. I'm not an expert in this, but as far as I can tell, there is some issue translating the 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
But for the record here is the Swift code in progress! Note it's hard coded to WAVE files for the moment... Perhaps someone else can finish this?
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
}