我正在使用 TinySoundFont 在 watchOS 上使用 SF2 文件。我想实时播放框架生成的原始音频（这意味着按下相应按钮后立即调用
tsf_note_ontsf_render_short尽管当我将其渲染到文件中时声音渲染得很好，但使用 AVAudioSourceNode 播放时确实很吵。 （根据 Rob Napier 的答案，这可能是因为我忽略了时间戳属性 - 我正在寻找解决该问题的解决方案。）是什么导致了此问题以及如何修复它？
我正在寻找一种实时渲染音频而不是预先计算音频的解决方案，因为我也想正确处理循环声音。
import SwiftUI
import AVFoundation
struct ContentView: View {
@ObservedObject var settings = Settings.shared
init() {
settings.prepare()
}
var body: some View {
Button("Play Sound") {
Settings.shared.playSound()
if !settings.engine.isRunning {
do {
try settings.engine.start()
} catch {
print(error)
}
}
}
}
}
import SwiftUI
import AVFoundation
class Settings: ObservableObject {
static let shared = Settings()
var engine: AVAudioEngine!
var sourceNode: AVAudioSourceNode!
var tinySoundFont: OpaquePointer!
func prepare() {
let soundFontPath = Bundle.main.path(forResource: "GMGSx", ofType: "sf2")
tinySoundFont = tsf_load_filename(soundFontPath)
tsf_set_output(tinySoundFont, TSF_MONO, 44100, 0)
setUpSound()
}
func setUpSound() {
if let engine = engine,
let sourceNode = sourceNode {
engine.detach(sourceNode)
}
engine = .init()
let mixerNode = engine.mainMixerNode
let audioFormat = AVAudioFormat(
commonFormat: .pcmFormatInt16,
sampleRate: 44100,
channels: 1,
interleaved: false
)
guard let audioFormat = audioFormat else {
return
}
sourceNode = AVAudioSourceNode(format: audioFormat) { silence, timeStamp, frameCount, audioBufferList in
guard let data = self.getSound(length: Int(frameCount)) else {
return 1
}
let ablPointer = UnsafeMutableAudioBufferListPointer(audioBufferList)
data.withUnsafeBytes { (intPointer: UnsafePointer<Int16>) in
for index in 0 ..< Int(frameCount) {
let value = intPointer[index]
// Set the same value on all channels (due to the inputFormat, there's only one channel though).
for buffer in ablPointer {
let buf: UnsafeMutableBufferPointer<Int16> = UnsafeMutableBufferPointer(buffer)
buf[index] = value
}
}
}
return noErr
}
engine.attach(sourceNode)
engine.connect(sourceNode, to: mixerNode, format: audioFormat)
do {
try AVAudioSession.sharedInstance().setCategory(.playback)
} catch {
print(error)
}
}
func playSound() {
tsf_note_on(tinySoundFont, 0, 60, 1)
}
func getSound(length: Int) -> Data? {
let array = [Int16]()
var storage = UnsafeMutablePointer<Int16>.allocate(capacity: length)
storage.initialize(from: array, count: length)
tsf_render_short(tinySoundFont, storage, Int32(length), 0)
let data = Data(bytes: storage, count: length)
storage.deallocate()
return data
}
}
AVAudioSourceNode在您的块中，您在每个渲染周期重新计算整个 WAV，然后将其写入磁盘，然后从磁盘读取它，然后填充所请求的块。您忽略请求的时间戳，并始终从样本零开始填充缓冲区。不匹配是引起嗡嗡声的原因。事实上，你的速度太慢可能是导致音调下降的原因。
根据文件的大小，实现此目的的最简单方法是首先将所有内容解码到内存中，然后填充请求的时间戳和长度的缓冲区。看起来您的 C 代码已经生成了 PCM 数据，因此无需将其转换为 WAV 文件。它似乎已经是正确的格式了。
Apple 为 Signal Generator 提供了一个很好的示例项目，您应该将其用作起点。下载它并确保它按预期工作。然后交换您的 SF2 代码。您可能还会发现这方面的视频很有帮助：AVAudioEngine 中的新增功能。
这里使用的最简单的工具可能是 AVAudioPlayerNode。您的 SoundFontHelper 使事情变得更加复杂，因此我将其删除并直接从 Swift 调用 TSF。为此，请创建一个名为
tsf.c#define TSF_IMPLEMENTATION
#include "tsf.h"
并将其添加到
BridgingHeader.h#import "tsf.h"
将 ContentView 简化为：
import SwiftUI
struct ContentView: View {
@ObservedObject var settings = Settings.shared
init() {
// You'll want error handling here.
try! settings.prepare()
}
var body: some View {
Button("Play Sound") {
settings.play()
}
}
}
剩下新版本的“设置”，这就是它的核心：
import SwiftUI
import AVFoundation
class Settings: ObservableObject {
static let shared = Settings()
var engine = AVAudioEngine()
let playerNode = AVAudioPlayerNode()
var tsf: OpaquePointer
var outputFormat = AVAudioFormat()
init() {
let soundFontPath = Bundle.main.path(forResource: "GMGSx", ofType: "sf2")
tsf = tsf_load_filename(soundFontPath)
engine.attach(playerNode)
engine.connect(playerNode, to: engine.mainMixerNode, format: nil)
updateOutputFormat()
}
// For simplicity, this object assumes the outputFormat does not change during its lifetime.
// It's important to watch for route changes, and recreate this object if they occur. For details, see:
// https://developer.apple.com/documentation/avfaudio/avaudiosession/responding_to_audio_session_route_changes
func updateOutputFormat() {
outputFormat = engine.mainMixerNode.outputFormat(forBus: 0)
}
func prepare() throws {
// Start the engine
try AVAudioSession.sharedInstance().setCategory(.playback)
try engine.start()
playerNode.play()
updateOutputFormat()
// Configure TSF. The only important thing here is the sample rate, which can be different on different hardware.
// Core Audio has a defined format of "deinterleaved 32-bit floating point."
tsf_set_output(tsf,
TSF_STEREO_UNWEAVED, // mode
Int32(outputFormat.sampleRate), // sampleRate
0) // gain
}
func play() {
tsf_note_on(tsf,
0, // preset_index
60, // key (middle C)
1.0) // velocity
// These tones have a long falloff, so you want a lot of source data. This is 10s.
let frameCount = 10 * Int(outputFormat.sampleRate)
// Create a buffer for the samples
let buffer = AVAudioPCMBuffer(pcmFormat: outputFormat, frameCapacity: AVAudioFrameCount(frameCount))!
buffer.frameLength = buffer.frameCapacity
// Render the samples. Do not mix. This buffer has been extended to
// the needed size by the assignment to `frameLength` above. The call to
// `assumingMemoryBound` is known to be correct because the format is Float32.
let ptr = buffer.audioBufferList.pointee.mBuffers.mData?.assumingMemoryBound(to: Float.self)
tsf_render_float(tsf,
ptr, // buffer
Int32(frameCount), // samples
0) // mixing (do not mix)
// All done. Play the buffer, interrupting whatever is currently playing
playerNode.scheduleBuffer(buffer, at: nil, options: .interrupts)
}
}
您可以在我的叉子找到完整版本。您还可以看到第一个提交，这是维护 SoundFontHelper 并进行转换来处理它的另一种方法，但首先正确渲染音频要简单得多。