怎样在 AVAssetReader 中应用数字信号处理来过滤高频声音
在 AVAssetReader
中应用数字信号处理(DSP)来过滤高频声音,通常需要以下几个步骤:
AVAssetReader
�� AVAssetReaderTrackOutput
:从媒体文件中读取音频数据。AVAssetReaderTrackOutput
中提取音频样本。以下是一个基本的示例代码,展示了如何使用 AVAssetReader
读取音频数据并应用高频滤波器:
import AVFoundation
import Accelerate
func applyHighFrequencyFilter(to asset: AVAsset, cutoffFrequency: Float) {
guard let audioTrack = asset.tracks(withMediaType: .audio).first else {
print("No audio track found")
return
}
do {
let assetReader = try AVAssetReader(asset: asset)
let outputSettings: [String: Any] = [
AVFormatIDKey: kAudioFormatLinearPCM,
AVLinearPCMIsFloatKey: true,
AVLinearPCMBitDepthKey: 32,
AVLinearPCMIsNonInterleaved: false
]
let trackOutput = AVAssetReaderTrackOutput(track: audioTrack, outputSettings: outputSettings)
assetReader.add(trackOutput)
assetReader.startReading()
var audioBufferList = AudioBufferList()
var audioBuffer = AudioBuffer()
audioBufferList.mNumberBuffers = 1
audioBufferList.mBuffers = audioBuffer
while assetReader.status == .reading {
if let sampleBuffer = trackOutput.copyNextSampleBuffer(),
let blockBuffer = CMSampleBufferGetDataBuffer(sampleBuffer) {
var length = 0
var dataPointer: UnsafeMutablePointer<Int8>?
CMBlockBufferGetDataPointer(blockBuffer, atOffset: 0, lengthAtOffsetOut: &length, totalLengthOut: &length, dataPointerOut: &dataPointer)
if let dataPointer = dataPointer {
let data = UnsafeMutableRawPointer(dataPointer).assumingMemoryBound(to: Float.self)
let frameCount = length / MemoryLayout<Float>.size
// Apply high-frequency filter
var filterState = [Float](repeating: 0, count: 2)
let nyquist = 0.5 * 44100.0
let normalizedCutoff = cutoffFrequency / Float(nyquist)
var coefficients = [Float](repeating: 0, count: 5)
vDSP_biquad_CreateLowPass(&coefficients, normalizedCutoff, 0.707)
vDSP_biquad(&coefficients, &filterState, data, 1, data, 1, vDSP_Length(frameCount))
// Processed data is now in `data`
// You can save or play the processed data here
}
CMSampleBufferInvalidate(sampleBuffer)
}
}
if assetReader.status == .completed {
print("Processing completed")
} else {
print("Processing failed with status: \(assetReader.status)")
}
} catch {
print("Error: \(error)")
}
}
创建 AVAssetReader
和 AVAssetReaderTrackOutput
:
AVAsset
中获取音频轨道,并创建 AVAssetReader
和 AVAssetReaderTrackOutput
来读取音频数据。读取音频样本:
copyNextSampleBuffer
方法从 AVAssetReaderTrackOutput
中提取音频样本。应用数字信号处理:
vDSP_biquad
函数应用高频滤波器。这里使用了双二阶滤波器(biquad filter),你可以根据需要调整滤波器的类型和参数。输出处理后的音频数据:
data
中,你可以将其保存到文件或进行播放。请