iOS|iOS 使用CoreAudio生成白噪音频数据
【iOS|iOS 使用CoreAudio生成白噪音频数据】iOS 使用CoreAudio生成白噪音频数据（空白音频）
/// 生成一段白噪音频数据
/// - Parameters:
///- startFrm: 开始frame
///- nFrames: 持续的frame
///- sampleRate: fps
///- numChannels: 声道数量
/// - Returns: 静音音频数据
static func createSilentAudio(startFrm: Int64, nFrames: Int, sampleRate: Float64, numChannels: UInt32) -> CMSampleBuffer? {
let bytesPerFrame = UInt32(2 * numChannels)
let blockSize = nFrames*Int(bytesPerFrame)var block: CMBlockBuffer?
var status = CMBlockBufferCreateWithMemoryBlock(
allocator: kCFAllocatorDefault,
memoryBlock: nil,
blockLength: blockSize,// blockLength
blockAllocator: nil,// blockAllocator
customBlockSource: nil,// customBlockSource
offsetToData: 0,// offsetToData
dataLength: blockSize,// dataLength
flags: 0,// flags
blockBufferOut: &block
)
assert(status == kCMBlockBufferNoErr)// we seem to get zeros from the above, but I can't find it documented. so... memset:
status = CMBlockBufferFillDataBytes(with: 0, blockBuffer: block!, offsetIntoDestination: 0, dataLength: blockSize)
assert(status == kCMBlockBufferNoErr)var asbd = AudioStreamBasicDescription(
mSampleRate: sampleRate,
mFormatID: kAudioFormatLinearPCM,
mFormatFlags: kLinearPCMFormatFlagIsSignedInteger,
mBytesPerPacket: bytesPerFrame,
mFramesPerPacket: 1,
mBytesPerFrame: bytesPerFrame,
mChannelsPerFrame: numChannels,
mBitsPerChannel: 16,
mReserved: 0
)var formatDesc: CMAudioFormatDescription?
status = CMAudioFormatDescriptionCreate(allocator: kCFAllocatorDefault, asbd: &asbd, layoutSize: 0, layout: nil, magicCookieSize: 0, magicCookie: nil, extensions: nil, formatDescriptionOut: &formatDesc)
assert(status == noErr)var sampleBuffer: CMSampleBuffer?// born ready
status = CMAudioSampleBufferCreateReadyWithPacketDescriptions(
allocator: kCFAllocatorDefault,
dataBuffer: block!,// dataBuffer
formatDescription: formatDesc!,
sampleCount: nFrames,// numSamples
presentationTimeStamp: CMTimeMake(value: startFrm, timescale: Int32(sampleRate)),// sbufPTS
packetDescriptions: nil,// packetDescriptions
sampleBufferOut: &sampleBuffer
)
assert(status == noErr)return sampleBuffer
}
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