feat:mp3 (#3)

---------

Co-authored-by: intelligence <intelligence@debian.local>
Reviewed-on: #3

macos/Sources/Transui/AppModel.swift

@@ -145,8 +145,12 @@ final class AppModel: ObservableObject {
     Task {
       defer { try? FileManager.default.removeItem(at: recording) }
       do {
+        let encoded = try await Task.detached(priority: .userInitiated) {
+          try MP3Encoder.encode(wav: recording)
+        }.value
+        defer { try? FileManager.default.removeItem(at: encoded) }
         let text = try await transcriptionClient.transcribe(
-          recording: recording,
+          recording: encoded,
           plan: transcriptionPlan,
           prompt: settings.prompt
         )

macos/Sources/Transui/MP3Encoder.swift

@@ -0,0 +1,90 @@
+import Foundation
+
+enum MP3EncodingError: LocalizedError {
+  case invalidRecording
+  case encodingFailed
+
+  var errorDescription: String? {
+    switch self {
+    case .invalidRecording: "The recording could not be read."
+    case .encodingFailed: "The recording could not be compressed."
+    }
+  }
+}
+
+enum MP3Encoder {
+  static func encode(wav url: URL) throws -> URL {
+    let wav = try Data(contentsOf: url, options: .mappedIfSafe)
+    let pcm = try pcmData(fromWAV: wav)
+    var encodedBytes: UnsafeMutablePointer<UInt8>?
+    var encodedSize = 0
+    let result = pcm.withUnsafeBytes { bytes in
+      transui_mp3_encode_mono_16k_32kbps(
+        bytes.bindMemory(to: UInt8.self).baseAddress,
+        bytes.count,
+        &encodedBytes,
+        &encodedSize
+      )
+    }
+    guard result == TRANSUI_MP3_OK, let encodedBytes, encodedSize > 0 else {
+      transui_mp3_free(encodedBytes)
+      throw MP3EncodingError.encodingFailed
+    }
+    defer { transui_mp3_free(encodedBytes) }
+
+    let output = FileManager.default.temporaryDirectory
+      .appendingPathComponent("transui-\(UUID().uuidString).mp3")
+    try Data(bytes: encodedBytes, count: encodedSize).write(to: output, options: .atomic)
+    return output
+  }
+
+  static func pcmData(fromWAV wav: Data) throws -> Data {
+    guard wav.count >= 12,
+      String(decoding: wav[0..<4], as: UTF8.self) == "RIFF",
+      String(decoding: wav[8..<12], as: UTF8.self) == "WAVE"
+    else { throw MP3EncodingError.invalidRecording }
+
+    var formatIsSupported = false
+    var audio: Data?
+    var offset = 12
+    while offset <= wav.count - 8 {
+      let chunkName = String(decoding: wav[offset..<(offset + 4)], as: UTF8.self)
+      let chunkSize = Int(readUInt32(wav, at: offset + 4))
+      let contentOffset = offset + 8
+      guard chunkSize >= 0, contentOffset <= wav.count,
+        chunkSize <= wav.count - contentOffset
+      else { throw MP3EncodingError.invalidRecording }
+
+      if chunkName == "fmt ", chunkSize >= 16 {
+        formatIsSupported = readUInt16(wav, at: contentOffset) == 1
+          && readUInt16(wav, at: contentOffset + 2) == 1
+          && readUInt32(wav, at: contentOffset + 4) == 16_000
+          && readUInt16(wav, at: contentOffset + 14) == 16
+      } else if chunkName == "data" {
+        audio = wav.subdata(in: contentOffset..<(contentOffset + chunkSize))
+      }
+
+      let paddedSize = chunkSize + (chunkSize & 1)
+      guard paddedSize <= Int.max - contentOffset else {
+        throw MP3EncodingError.invalidRecording
+      }
+      offset = contentOffset + paddedSize
+    }
+
+    guard formatIsSupported, let audio, !audio.isEmpty, audio.count.isMultiple(of: 2) else {
+      throw MP3EncodingError.invalidRecording
+    }
+    return audio
+  }
+
+  private static func readUInt16(_ data: Data, at offset: Int) -> UInt16 {
+    UInt16(data[offset]) | UInt16(data[offset + 1]) << 8
+  }
+
+  private static func readUInt32(_ data: Data, at offset: Int) -> UInt32 {
+    UInt32(data[offset])
+      | UInt32(data[offset + 1]) << 8
+      | UInt32(data[offset + 2]) << 16
+      | UInt32(data[offset + 3]) << 24
+  }
+}

macos/Sources/Transui/TranscriptionClient.swift

@@ -146,8 +146,8 @@ struct TranscriptionClient {
     if !model.isEmpty { field("model", model) }
     if !prompt.isEmpty { field("prompt", prompt) }
     data.append("--\(boundary)\r\n")
-    data.append("Content-Disposition: form-data; name=\"file\"; filename=\"recording.wav\"\r\n")
-    data.append("Content-Type: audio/wav\r\n\r\n")
+    data.append("Content-Disposition: form-data; name=\"file\"; filename=\"recording.mp3\"\r\n")
+    data.append("Content-Type: audio/mpeg\r\n\r\n")
     data.append(try Data(contentsOf: recording))
     data.append("\r\n--\(boundary)--\r\n")
     return data

macos/Sources/Transui/Transui-Bridging-Header.h

@@ -0,0 +1 @@
+#include "transui_mp3.h"

macos/Tests/TransuiTests/MP3EncoderTests.swift

@@ -0,0 +1,45 @@
+import XCTest
+
+@testable import Transui
+
+final class MP3EncoderTests: XCTestCase {
+  func testExtractsSupportedPCMDataFromWAV() throws {
+    let samples = Data([0x01, 0x02, 0x03, 0x04])
+    let wav = makeWAV(samples: samples)
+
+    XCTAssertEqual(try MP3Encoder.pcmData(fromWAV: wav), samples)
+  }
+
+  func testRejectsWrongSampleRate() {
+    XCTAssertThrowsError(try MP3Encoder.pcmData(fromWAV: makeWAV(sampleRate: 44_100)))
+  }
+
+  private func makeWAV(sampleRate: UInt32 = 16_000, samples: Data = Data([0, 0])) -> Data {
+    var data = Data("RIFF".utf8)
+    append(UInt32(36 + samples.count), to: &data)
+    data.append(Data("WAVEfmt ".utf8))
+    append(UInt32(16), to: &data)
+    append(UInt16(1), to: &data)
+    append(UInt16(1), to: &data)
+    append(sampleRate, to: &data)
+    append(sampleRate * 2, to: &data)
+    append(UInt16(2), to: &data)
+    append(UInt16(16), to: &data)
+    data.append(Data("data".utf8))
+    append(UInt32(samples.count), to: &data)
+    data.append(samples)
+    return data
+  }
+
+  private func append(_ value: UInt16, to data: inout Data) {
+    data.append(UInt8(value & 0xff))
+    data.append(UInt8(value >> 8))
+  }
+
+  private func append(_ value: UInt32, to data: inout Data) {
+    data.append(UInt8(value & 0xff))
+    data.append(UInt8((value >> 8) & 0xff))
+    data.append(UInt8((value >> 16) & 0xff))
+    data.append(UInt8((value >> 24) & 0xff))
+  }
+}

macos/project.yml

@@ -24,6 +24,8 @@ targets:
     deploymentTarget: "15.0"
     sources:
       - path: Sources/Transui
+      - path: ../third_party/transui_mp3
+      - path: ../third_party/shine/src/lib
     settings:
       base:
         CODE_SIGN_ENTITLEMENTS: Transui.entitlements
@@ -32,6 +34,11 @@ targets:
         INFOPLIST_FILE: Info.plist
         PRODUCT_BUNDLE_IDENTIFIER: io.github.transui.macos
         PRODUCT_NAME: Transui
+        GCC_C_LANGUAGE_STANDARD: c11
+        HEADER_SEARCH_PATHS:
+          - "$(SRCROOT)/../third_party/transui_mp3"
+          - "$(SRCROOT)/../third_party/shine/src/lib"
+        SWIFT_OBJC_BRIDGING_HEADER: Sources/Transui/Transui-Bridging-Header.h
 
   TransuiTests:
     type: bundle.unit-test