将问题中的源代码更新为 Swift 4 并将其包装在一个类中。信用去往Castles and 节奏拳手获取原始源代码和答案。留下作者的评论，添加一些断言和打印语句以进行调试。在 iOS 上测试。
输出文件的比特率硬编码为 96kb/s，您可以轻松覆盖该值。我要转换的大多数音频文件都是 320kb/s，因此我使用此类来压缩文件以供离线存储。压缩结果位于此答案的底部。
Usage:
let inputFilePath = URL(fileURLWithPath: "/path/to/file.mp3")
let outputFileURL = URL(fileURLWithPath: "/path/to/output/compressed.mp4")
if let audioConverter = AVAudioFileConverter(inputFileURL: inputFilePath, outputFileURL: outputFileURL) {
audioConverter.convert()
}
Class
import AVFoundation
final class AVAudioFileConverter {
var rwAudioSerializationQueue: DispatchQueue!
var asset:AVAsset!
var assetReader:AVAssetReader!
var assetReaderAudioOutput:AVAssetReaderTrackOutput!
var assetWriter:AVAssetWriter!
var assetWriterAudioInput:AVAssetWriterInput!
var outputURL:URL
var inputURL:URL
init?(inputFileURL: URL, outputFileURL: URL) {
inputURL = inputFileURL
outputURL = outputFileURL
if (FileManager.default.fileExists(atPath: inputURL.absoluteString)) {
print("Input file does not exist at file path \(inputURL.absoluteString)")
return nil
}
}
func convert() {
let rwAudioSerializationQueueDescription = " rw audio serialization queue"
// Create the serialization queue to use for reading and writing the audio data.
rwAudioSerializationQueue = DispatchQueue(label: rwAudioSerializationQueueDescription)
assert(rwAudioSerializationQueue != nil, "Failed to initialize Dispatch Queue")
asset = AVAsset(url: inputURL)
assert(asset != nil, "Error creating AVAsset from input URL")
print("Output file path -> ", outputURL.absoluteString)
asset.loadValuesAsynchronously(forKeys: ["tracks"], completionHandler: {
var success = true
var localError:NSError?
success = (self.asset.statusOfValue(forKey: "tracks", error: &localError) == AVKeyValueStatus.loaded)
// Check for success of loading the assets tracks.
if (success) {
// If the tracks loaded successfully, make sure that no file exists at the output path for the asset writer.
let fm = FileManager.default
let localOutputPath = self.outputURL.path
if (fm.fileExists(atPath: localOutputPath)) {
do {
try fm.removeItem(atPath: localOutputPath)
success = true
} catch {
print("Error trying to remove output file at path -> \(localOutputPath)")
}
}
}
if (success) {
success = self.setupAssetReaderAndAssetWriter()
} else {
print("Failed setting up Asset Reader and Writer")
}
if (success) {
success = self.startAssetReaderAndWriter()
return
} else {
print("Failed to start Asset Reader and Writer")
}
})
}
func setupAssetReaderAndAssetWriter() -> Bool {
do {
assetReader = try AVAssetReader(asset: asset)
} catch {
print("Error Creating AVAssetReader")
}
do {
assetWriter = try AVAssetWriter(outputURL: outputURL, fileType: AVFileType.m4a)
} catch {
print("Error Creating AVAssetWriter")
}
var assetAudioTrack:AVAssetTrack? = nil
let audioTracks = asset.tracks(withMediaType: AVMediaType.audio)
if (audioTracks.count > 0) {
assetAudioTrack = audioTracks[0]
}
if (assetAudioTrack != nil) {
let decompressionAudioSettings:[String : Any] = [
AVFormatIDKey:Int(kAudioFormatLinearPCM)
]
assetReaderAudioOutput = AVAssetReaderTrackOutput(track: assetAudioTrack!, outputSettings: decompressionAudioSettings)
assert(assetReaderAudioOutput != nil, "Failed to initialize AVAssetReaderTrackOutout")
assetReader.add(assetReaderAudioOutput)
var channelLayout = AudioChannelLayout()
memset(&channelLayout, 0, MemoryLayout<AudioChannelLayout>.size);
channelLayout.mChannelLayoutTag = kAudioChannelLayoutTag_Stereo;
let outputSettings:[String : Any] = [
AVFormatIDKey: Int(kAudioFormatMPEG4AAC),
AVSampleRateKey: 44100,
AVEncoderBitRateKey: 96000,
AVNumberOfChannelsKey: 2,
AVChannelLayoutKey: NSData(bytes:&channelLayout, length:MemoryLayout<AudioChannelLayout>.size)]
assetWriterAudioInput = AVAssetWriterInput(mediaType: AVMediaType.audio, outputSettings: outputSettings)
assert(rwAudioSerializationQueue != nil, "Failed to initialize AVAssetWriterInput")
assetWriter.add(assetWriterAudioInput)
}
print("Finsihed Setup of AVAssetReader and AVAssetWriter")
return true
}
func startAssetReaderAndWriter() -> Bool {
print("STARTING ASSET WRITER")
assetWriter.startWriting()
assetReader.startReading()
assetWriter.startSession(atSourceTime: kCMTimeZero)
assetWriterAudioInput.requestMediaDataWhenReady(on: rwAudioSerializationQueue, using: {
while(self.assetWriterAudioInput.isReadyForMoreMediaData ) {
var sampleBuffer = self.assetReaderAudioOutput.copyNextSampleBuffer()
if(sampleBuffer != nil) {
self.assetWriterAudioInput.append(sampleBuffer!)
sampleBuffer = nil
} else {
self.assetWriterAudioInput.markAsFinished()
self.assetReader.cancelReading()
self.assetWriter.finishWriting {
print("Asset Writer Finished Writing")
}
break
}
}
})
return true
}
}
输入文件：17.3 MB
// generated with afinfo on mac
File: D290A73C37B777F1.mp3
File type ID: MPG3
Num Tracks: 1
----
Data format: 2 ch, 44100 Hz, '.mp3' (0x00000000) 0 bits/channel, 0 bytes/packet, 1152 frames/packet, 0 bytes/frame
no channel layout.
estimated duration: 424.542025 sec
audio bytes: 16981681
audio packets: 16252
bit rate: 320000 bits per second
packet size upper bound: 1052
maximum packet size: 1045
audio data file offset: 322431
optimized
audio 18720450 valid frames + 576 priming + 1278 remainder = 18722304
----
输出文件：5.1 MB
// generated with afinfo on Mac
File: compressed.m4a
File type ID: m4af
Num Tracks: 1
----
Data format: 2 ch, 44100 Hz, 'aac ' (0x00000000) 0 bits/channel, 0 bytes/packet, 1024 frames/packet, 0 bytes/frame
Channel layout: Stereo (L R)
estimated duration: 424.542041 sec
audio bytes: 5019294
audio packets: 18286
bit rate: 94569 bits per second
packet size upper bound: 763
maximum packet size: 763
audio data file offset: 44
not optimized
audio 18722304 valid frames + 2112 priming + 448 remainder = 18724864
format list:
[ 0] format: 2 ch, 44100 Hz, 'aac ' (0x00000000) 0 bits/channel, 0 bytes/packet, 1024 frames/packet, 0 bytes/frame
Channel layout: Stereo (L R)
----
