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zero-alloc audio pipeline: pointer-based IO from ring buffer to stdout

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Replace Data/AudioPacket allocations with raw pointer callbacks through
the entire audio pipeline. Ring buffer hands out direct pointers (or
linearizes into a pre-allocated scratch buffer on wrap-around), converter
accepts/emits pointers via its cached buffers, and output handler writes
to stdout via write(2) with EINTR handling.

Remove AudioPacket (dead code), --flush flag (no-op with raw write(2)).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
This commit is contained in:
Nick Payne
2026-03-07 07:14:16 +00:00
parent 65c2d58c82
commit a1eb465142
9 changed files with 122 additions and 174 deletions
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Sources/AudioTeeCore/Core/AudioFormatConverter.swift
+20 -26
View File
@@ -126,27 +126,28 @@ public class AudioFormatConverter {
return (inputBuf, outputBuf)
}
public func transform(_ packet: AudioPacket) -> AudioPacket {
let inputData = packet.data
// Calculate frame count from the input data size
/// Converts audio data in-place through the pre-allocated converter buffers.
/// Calls `handler` with a pointer to the converted output, valid only for
/// the duration of that call. Returns false on failure (caller should
/// pass through the original data or drop it).
@discardableResult
public func transform(
from source: UnsafeRawPointer, count: Int,
handler: (UnsafeRawPointer, Int) -> Void
) -> Bool {
let bytesPerFrame = Int(sourceFormat.streamDescription.pointee.mBytesPerFrame)
let inputFrameCount = AVAudioFrameCount(inputData.count / bytesPerFrame)
let inputFrameCount = AVAudioFrameCount(count / bytesPerFrame)
// Get or create pre-allocated buffers
guard let (inputBuffer, outputBuffer) = getBuffers(inputFrameCount: inputFrameCount) else {
return packet
return false
}
// Copy input data into the reusable input buffer
inputData.withUnsafeBytes { bytes in
let dest = inputBuffer.audioBufferList.pointee.mBuffers.mData!
dest.copyMemory(from: bytes.baseAddress!, byteCount: inputData.count)
}
// Copy source data into the reusable input buffer
let dest = inputBuffer.audioBufferList.pointee.mBuffers.mData!
dest.copyMemory(from: source, byteCount: count)
inputBuffer.frameLength = inputFrameCount
// Perform conversion — the block-based API lets AVAudioConverter pull
// input data as needed. We do NOT call avConverter.reset() between
// Perform conversion — we do NOT call avConverter.reset() between
// calls because the resampler maintains internal state for continuity
// across chunks (avoiding discontinuity artifacts).
var error: NSError?
@@ -157,7 +158,6 @@ public class AudioFormatConverter {
return inputBuffer
}
// Check if conversion produced output (regardless of status code)
guard outputBuffer.frameLength > 0 else {
AudioTeeLogging.logger.error(
"Audio conversion produced no output",
@@ -167,19 +167,13 @@ public class AudioFormatConverter {
"input_frames": String(inputBuffer.frameLength),
"output_capacity": String(outputBuffer.frameCapacity),
])
return packet
return false
}
// Extract converted data from the reusable output buffer
let outputData = Data(
bytes: outputBuffer.audioBufferList.pointee.mBuffers.mData!,
count: Int(outputBuffer.frameLength * targetFormat.streamDescription.pointee.mBytesPerFrame))
return AudioPacket(
timestamp: packet.timestamp,
duration: packet.duration,
data: outputData
)
let outputCount = Int(
outputBuffer.frameLength * targetFormat.streamDescription.pointee.mBytesPerFrame)
handler(outputBuffer.audioBufferList.pointee.mBuffers.mData!, outputCount)
return true
}
public static func toSampleRate(