本文继续探讨 AudioToolBox 与 wav 播放器的那些事情
播放套路三步走:
先读数据,文件还原采样数据
对于音频资源文件,使用 Audio File Services, 和 Audio File Stream Services
这一步,下面两篇博客,都重点探讨了,
从 wav 播放器,学习 AudioToolBox 的 services
从 pcm 播放器,继续学习 AudioToolBox 的 services 与非压缩格式
采样数据,集中为音频缓冲
把 pcm buffer 交给 AVAudioPlayerNode ,就可以播放了
第三步,比较简单
本篇重点,探讨第二步,采样数据,转 buffer
本篇中,把第一步合并入了第二步
采样数据,转音频缓冲的常规做法
弄一个计时器,不停的调用下面的方法,通过 AVAudioPCMBuffer
走回调,产生新的 buffer,
直到读完数据,抛出异常 reachedEndOfFile
走到底,let isEndOfData = packetIndex >= packets.count - 1
,
就返回
public func read(_ frames: AVAudioFrameCount) throws -> AVAudioPCMBuffer {
let framesPerPacket = readFormat.streamDescription.pointee.mFramesPerPacket
var packets = frames / framesPerPacket
// 新建 buffer
guard let buffer = AVAudioPCMBuffer(pcmFormat: readFormat, frameCapacity: frames) else {
throw ReaderError.failedToCreatePCMBuffer
}
buffer.frameLength = frames
// 填充数据
try queue.sync {
let context = unsafeBitCast(self, to: UnsafeMutableRawPointer.self)
let status = AudioConverterFillComplexBuffer(converter!, ReaderConverterCallback, context, &packets, buffer.mutableAudioBufferList, nil)
guard status == noErr else {
// ...
throw ReaderError.reachedEndOfFile
}
}
return buffer
}
通过 AVAudioPCMBuffer
走下面的回调,
重点是这一行 reader.currentPacket = reader.currentPacket + 1
,
这里是数据源 reader.parser.packetsX
, 从数据源中拿一个数据,进一位,
func ReaderConverterCallback(_ converter: AudioConverterRef,
_ packetCount: UnsafeMutablePointer<UInt32>,
_ ioData: UnsafeMutablePointer<AudioBufferList>,
_ outPacketDescriptions: UnsafeMutablePointer<UnsafeMutablePointer<AudioStreamPacketDescription>?>?,
_ context: UnsafeMutableRawPointer?) -> OSStatus {
let reader = Unmanaged<Reader>.fromOpaque(context!).takeUnretainedValue()
guard let _ = reader.parser.dataFormatD else {
return ReaderMissingSourceFormatError
}
let packetIndex = Int(reader.currentPacket)
let packets = reader.parser.packetsX
let isEndOfData = packetIndex >= packets.count - 1
if isEndOfData {
packetCount.pointee = 0
return ReaderReachedEndOfDataError
}
var data = packets[packetIndex]
let dataCount = data.count
ioData.pointee.mNumberBuffers = 1
ioData.pointee.mBuffers.mData = UnsafeMutableRawPointer.allocate(byteCount: dataCount, alignment: 0)
_ = data.withUnsafeMutableBytes { (bytes: UnsafeMutablePointer<UInt8>) in
memcpy((ioData.pointee.mBuffers.mData?.assumingMemoryBound(to: UInt8.self))!, bytes, dataCount)
}
ioData.pointee.mBuffers.mDataByteSize = UInt32(dataCount)
packetCount.pointee = 1
reader.currentPacket = reader.currentPacket + 1
return noErr
}
重点是 seek
拖动进度条,跳转时间,
我们拿到一个时刻,先用方法 frameOffset
算出当前是哪一帧,
对于 pcm, 一个包 packet 里面就一帧 frame,
方法 packetOffset
, 没做什么事
调用播放节点的停止方法,playerNode.stop()
,清空分配给播放节点的音频缓冲 buffer,
拿到包的序号,指定给上面代码中的 currentPacket ,
这样跳转播放时间,就是清空播放节点的音频缓冲,再从需要时刻的音频数据开始读取,分配相应的音频缓冲 buffer
给播放节点 playerNode
本文 github repo 中, 音频文件持续时间为 63.158 秒,有 1010528 帧 frame,
一秒钟 16000 帧 frame, 对应该音频文件 16000 Hz 的采样率
这种做法,缓存采样数据,seek 可以精确到具体的帧,seek 的精度很高,是 1/16000, 达到了 0.0000625 秒
guard let frameOffset = parser.frameOffset(forTime: time),
let packetOffset = parser.packetOffset(forFrame: frameOffset) else {
return
}
// ...
// 栈,排空
playerNode.stop()
volume = 0
// Perform the seek to the proper packet offset
do {
try reader.seek(packetOffset)
} catch {
os_log("Failed to seek: %@", log: Streamer.logger, type: .error, error.localizedDescription)
return
}
换一种做法,缓冲 AVAudioPCMBuffer
初始化的时候,读取音频文件,获取全部的采样数据,跟之前一样,
然后把采样数据,全部转化为音频 buffer,
上一种做法是,根据需要,拿对应的采样数据,去临时转化,产生想要的音频 buffer,
现在的做法是,根据需要,拿对应的音频 buffer,不需要去临时转化
先还原所有的采样数据,对应前面的 parser
再获取所有的 buffer
public required init(src path: URL, readFormat readF: AVAudioFormat, bufferSize size: AVAudioFrameCount) throws {
readFormat = readF
readBufferSize = size
Utility.check(error: AudioFileOpenURL(path as CFURL, .readPermission, 0, &playbackFile) , // set on output to the AudioFileID
operation: "AudioFileOpenURL failed")
guard let file = playbackFile else {
return
}
var numPacketsToRead: UInt32 = 0
GetPropertyValue(val: &numPacketsToRead, file: file, prop: kAudioFilePropertyAudioDataPacketCount)
var asbdFormat = AudioStreamBasicDescription()
GetPropertyValue(val: &asbdFormat, file: file, prop: kAudioFilePropertyDataFormat)
dataFormatD = AVAudioFormat(streamDescription: &asbdFormat)
/// At this point we should definitely have a data format
var bytesRead: UInt32 = 0
GetPropertyValue(val: &bytesRead, file: file, prop: kAudioFilePropertyAudioDataByteCount)
guard let dataFormat = dataFormatD else {
return
}
let format = dataFormat.streamDescription.pointee
let bytesPerPacket = Int(format.mBytesPerPacket)
for i in 0 ..< Int(numPacketsToRead) {
var packetSize = UInt32(bytesPerPacket)
let packetStart = Int64(i * bytesPerPacket)
let dataPt: UnsafeMutableRawPointer = malloc(MemoryLayout<UInt8>.size * bytesPerPacket)
AudioFileReadBytes(file, false, packetStart, &packetSize, dataPt)
let startPt = dataPt.bindMemory(to: UInt8.self, capacity: bytesPerPacket)
let buffer = UnsafeBufferPointer(start: startPt, count: bytesPerPacket)
let array = Array(buffer)
packetsX.append(Data(array))
}
print("packetsX.count = \(packetsX.count)")
// 前面是合并的 parser
// 后面是获取所有的 buffer
let sourceFormat = dataFormat.streamDescription
let commonFormat = readF.streamDescription
let result = AudioConverterNew(sourceFormat, commonFormat, &converter)
guard result == noErr else {
throw ReaderError.unableToCreateConverter(result)
}
let framesPerPacket = readFormat.streamDescription.pointee.mFramesPerPacket
var packets = readBufferSize / framesPerPacket
// print("frames: \(frames)")
// print("framesPerPacket: \(framesPerPacket)")
totalPacketCount = AVAudioPacketCount(packetsX.count)
while true {
/// Allocate a buffer to hold the target audio data in the Read format
guard let buffer = AVAudioPCMBuffer(pcmFormat: readFormat, frameCapacity: readBufferSize) else {
throw ReaderError.failedToCreatePCMBuffer
}
buffer.frameLength = readBufferSize
// Try to read the frames from the parser
let context = unsafeBitCast(self, to: UnsafeMutableRawPointer.self)
let status = AudioConverterFillComplexBuffer(converter!, ReaderConverterCallback, context, &packets, buffer.mutableAudioBufferList, nil)
guard status == noErr else {
switch status {
case ReaderMissingSourceFormatError:
print("parserMissingDataFormat")
throw ReaderError.parserMissingDataFormat
case ReaderReachedEndOfDataError:
print("reachedEndOfFile: buffers.count = \(buffers.count)")
packetsX.removeAll()
return
case ReaderNotEnoughDataError:
print("notEnoughData")
throw ReaderError.notEnoughData
default:
print("converterFailed")
throw ReaderError.converterFailed(status)
}
}
buffers.append(buffer)
}
}
后面拿 buffer, 播放就简单了,
不需要转化
public func read() throws -> AVAudioPCMBuffer {
guard currentBuffer < buffers.count else {
throw ReaderError.reachedEndOfFile
}
let buff = buffers[currentBuffer]
currentBuffer += 1
return buff
}
重点还是 seek
拖动进度条,调整播放时间
这里没有精确到某一帧 Frame,
因 pcm 数据中 framesPerPacket
= 1, 一个包 packet = 一帧 frame
本文 github repo 中, 音频文件持续时间为 63.158 秒,有 1359 个音频 buffer,
( 本文当前采用的 buffer size 为 2 KB, 2048 )
一秒钟 21.517 个 音频 buffer,
一个音频 buffer, 对应 0.0465 秒
这种做法,缓存采样数据,seek 只能精确到具体的 buffer ,seek 的精度到了 0.0465 秒
上文 packet ( 也就是 pcm 下的 frame )的精度为 0.0000625 秒。
这个就看业务了,高保真音质应该不可接受,人声听听歌可接受
public func seek(buffer ratio: TimeInterval) throws {
currentBuffer = Int(TimeInterval(buffers.count) * ratio)
}
如本文采用 buffer size 为 4 KB, 4096,
则有 679 个 buffer, 音频持续时间 63.158 秒
一秒对应 10.75 个 buffer,
一个音频 buffer, 对应 0.093 秒
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