diff --git a/server/utils/ffmpegHelpers.js b/server/utils/ffmpegHelpers.js
index 28c6e618..2a242504 100644
--- a/server/utils/ffmpegHelpers.js
+++ b/server/utils/ffmpegHelpers.js
@@ -5,6 +5,7 @@ const os = require('os')
 const Path = require('path')
 const Logger = require('../Logger')
 const { filePathToPOSIX } = require('./fileUtils')
+const LibraryItem = require('../objects/LibraryItem')
 
 function escapeSingleQuotes(path) {
   // return path.replace(/'/g, '\'\\\'\'')
@@ -220,6 +221,14 @@ function generateFFMetadata(metadata, chapters) {
 
 module.exports.generateFFMetadata = generateFFMetadata
 
+/**
+ * Writes FFmpeg metadata file with the given metadata and chapters.
+ *
+ * @param {Object} metadata - The metadata object.
+ * @param {Array} chapters - The array of chapter objects.
+ * @param {string} ffmetadataPath - The path to the FFmpeg metadata file.
+ * @returns {Promise<boolean>} - A promise that resolves to true if the file was written successfully, false otherwise.
+ */
 async function writeFFMetadataFile(metadata, chapters, ffmetadataPath) {
   try {
     await fs.writeFile(ffmetadataPath, generateFFMetadata(metadata, chapters))
@@ -235,23 +244,25 @@ module.exports.writeFFMetadataFile = writeFFMetadataFile
 
 /**
  * Adds an ffmetadata and optionally a cover image to an audio file using fluent-ffmpeg.
+ *
  * @param {string} audioFilePath - Path to the input audio file.
  * @param {string|null} coverFilePath - Path to the cover image file.
  * @param {string} metadataFilePath - Path to the ffmetadata file.
  * @param {number} track - The track number to embed in the audio file.
  * @param {string} mimeType - The MIME type of the audio file.
+ * @param {Ffmpeg} ffmpeg - The Ffmpeg instance to use (optional). Used for dependency injection in tests.
+ * @returns {Promise<boolean>} A promise that resolves to true if the operation is successful, false otherwise.
  */
-async function addCoverAndMetadataToFile(audioFilePath, coverFilePath, metadataFilePath, track, mimeType) {
+async function addCoverAndMetadataToFile(audioFilePath, coverFilePath, metadataFilePath, track, mimeType, ffmpeg = Ffmpeg()) {
   const isMp4 = mimeType === 'audio/mp4'
   const isMp3 = mimeType === 'audio/mpeg'
 
   const audioFileDir = Path.dirname(audioFilePath)
   const audioFileExt = Path.extname(audioFilePath)
   const audioFileBaseName = Path.basename(audioFilePath, audioFileExt)
-  const tempFilePath = Path.join(audioFileDir, `${audioFileBaseName}.tmp${audioFileExt}`)
+  const tempFilePath = filePathToPOSIX(Path.join(audioFileDir, `${audioFileBaseName}.tmp${audioFileExt}`))
 
   return new Promise((resolve) => {
-    let ffmpeg = Ffmpeg()
     ffmpeg.input(audioFilePath).input(metadataFilePath).outputOptions([
       '-map 0:a', // map audio stream from input file
       '-map_metadata 1', // map metadata tags from metadata file first
@@ -318,6 +329,13 @@ function escapeFFMetadataValue(value) {
   return value.replace(/([;=\n\\#])/g, '\\$1')
 }
 
+/**
+ * Retrieves the FFmpeg metadata object for a given library item.
+ *
+ * @param {LibraryItem} libraryItem - The library item containing the media metadata.
+ * @param {number} audioFilesLength - The length of the audio files.
+ * @returns {Object} - The FFmpeg metadata object.
+ */
 function getFFMetadataObject(libraryItem, audioFilesLength) {
   const metadata = libraryItem.media.metadata
 
diff --git a/test/server/utils/ffmpegHelpers.test.js b/test/server/utils/ffmpegHelpers.test.js
new file mode 100644
index 00000000..82daf1ba
--- /dev/null
+++ b/test/server/utils/ffmpegHelpers.test.js
@@ -0,0 +1,249 @@
+const { expect } = require('chai')
+const sinon = require('sinon')
+const { generateFFMetadata, addCoverAndMetadataToFile } = require('../../../server/utils/ffmpegHelpers')
+const fs = require('../../../server/libs/fsExtra')
+const EventEmitter = require('events')
+
+global.isWin = process.platform === 'win32'
+
+describe('generateFFMetadata', () => {
+  function createTestSetup() {
+    const metadata = {
+      title: 'My Audiobook',
+      artist: 'John Doe',
+      album: 'Best Audiobooks'
+    }
+
+    const chapters = [
+      { start: 0, end: 1000, title: 'Chapter 1' },
+      { start: 1000, end: 2000, title: 'Chapter 2' }
+    ]
+
+    return { metadata, chapters }
+  }
+
+  let metadata = null
+  let chapters = null
+  beforeEach(() => {
+    const input = createTestSetup()
+    metadata = input.metadata
+    chapters = input.chapters
+  })
+
+  it('should generate ffmetadata content with chapters', () => {
+    const result = generateFFMetadata(metadata, chapters)
+
+    expect(result).to.equal(';FFMETADATA1\ntitle=My Audiobook\nartist=John Doe\nalbum=Best Audiobooks\n\n[CHAPTER]\nTIMEBASE=1/1000\nSTART=0\nEND=1000000\ntitle=Chapter 1\n\n[CHAPTER]\nTIMEBASE=1/1000\nSTART=1000000\nEND=2000000\ntitle=Chapter 2\n')
+  })
+
+  it('should generate ffmetadata content without chapters', () => {
+    chapters = null
+
+    const result = generateFFMetadata(metadata, chapters)
+
+    expect(result).to.equal(';FFMETADATA1\ntitle=My Audiobook\nartist=John Doe\nalbum=Best Audiobooks\n')
+  })
+
+  it('should handle chapters with no title', () => {
+    chapters = [
+      { start: 0, end: 1000 },
+      { start: 1000, end: 2000 }
+    ]
+
+    const result = generateFFMetadata(metadata, chapters)
+
+    expect(result).to.equal(';FFMETADATA1\ntitle=My Audiobook\nartist=John Doe\nalbum=Best Audiobooks\n\n[CHAPTER]\nTIMEBASE=1/1000\nSTART=0\nEND=1000000\n\n[CHAPTER]\nTIMEBASE=1/1000\nSTART=1000000\nEND=2000000\n')
+  })
+
+  it('should handle metadata escaping special characters (=, ;, #,  and a newline)', () => {
+    metadata.title = 'My Audiobook; with = special # characters\n'
+    chapters[0].title = 'Chapter #1'
+
+    const result = generateFFMetadata(metadata, chapters)
+
+    expect(result).to.equal(';FFMETADATA1\ntitle=My Audiobook\\; with \\= special \\# characters\\\n\nartist=John Doe\nalbum=Best Audiobooks\n\n[CHAPTER]\nTIMEBASE=1/1000\nSTART=0\nEND=1000000\ntitle=Chapter \\#1\n\n[CHAPTER]\nTIMEBASE=1/1000\nSTART=1000000\nEND=2000000\ntitle=Chapter 2\n')
+  })
+})
+
+describe('addCoverAndMetadataToFile', () => {
+  function createTestSetup() {
+    const audioFilePath = '/path/to/audio/file.mp3'
+    const coverFilePath = '/path/to/cover/image.jpg'
+    const metadataFilePath = '/path/to/metadata/file.txt'
+    const track = 1
+    const mimeType = 'audio/mpeg'
+
+    const ffmpegStub = new EventEmitter()
+    ffmpegStub.input = sinon.stub().returnsThis()
+    ffmpegStub.outputOptions = sinon.stub().returnsThis()
+    ffmpegStub.output = sinon.stub().returnsThis()
+    ffmpegStub.input = sinon.stub().returnsThis()
+    ffmpegStub.run = sinon.stub().callsFake(() => {
+      ffmpegStub.emit('end')
+    })
+    const fsCopyFileSyncStub = sinon.stub(fs, 'copyFileSync')
+    const fsUnlinkSyncStub = sinon.stub(fs, 'unlinkSync')
+
+    return { audioFilePath, coverFilePath, metadataFilePath, track, mimeType, ffmpegStub, fsCopyFileSyncStub, fsUnlinkSyncStub }
+  }
+
+  let audioFilePath = null
+  let coverFilePath = null
+  let metadataFilePath = null
+  let track = null
+  let mimeType = null
+  let ffmpegStub = null
+  let fsCopyFileSyncStub = null
+  let fsUnlinkSyncStub = null
+  beforeEach(() => {
+    const input = createTestSetup()
+    audioFilePath = input.audioFilePath
+    coverFilePath = input.coverFilePath
+    metadataFilePath = input.metadataFilePath
+    track = input.track
+    mimeType = input.mimeType
+    ffmpegStub = input.ffmpegStub
+    fsCopyFileSyncStub = input.fsCopyFileSyncStub
+    fsUnlinkSyncStub = input.fsUnlinkSyncStub
+  })
+
+  it('should add cover image and metadata to audio file', async () => {
+    // Act
+    const result = await addCoverAndMetadataToFile(audioFilePath, coverFilePath, metadataFilePath, track, mimeType, ffmpegStub)
+
+    // Assert
+    expect(result).to.be.true
+    expect(ffmpegStub.input.calledThrice).to.be.true
+    expect(ffmpegStub.input.getCall(0).args[0]).to.equal(audioFilePath)
+    expect(ffmpegStub.input.getCall(1).args[0]).to.equal(metadataFilePath)
+    expect(ffmpegStub.input.getCall(2).args[0]).to.equal(coverFilePath)
+
+    expect(ffmpegStub.outputOptions.callCount).to.equal(4)
+    expect(ffmpegStub.outputOptions.getCall(0).args[0]).to.deep.equal(['-map 0:a', '-map_metadata 1', '-map_metadata 0', '-map_chapters 1', '-c copy'])
+    expect(ffmpegStub.outputOptions.getCall(1).args[0]).to.deep.equal(['-metadata track=1'])
+    expect(ffmpegStub.outputOptions.getCall(2).args[0]).to.deep.equal(['-id3v2_version 3'])
+    expect(ffmpegStub.outputOptions.getCall(3).args[0]).to.deep.equal(['-map 2:v', '-disposition:v:0 attached_pic', '-metadata:s:v', 'title=Cover', '-metadata:s:v', 'comment=Cover'])
+
+    expect(ffmpegStub.output.calledOnce).to.be.true
+    expect(ffmpegStub.output.firstCall.args[0]).to.equal('/path/to/audio/file.tmp.mp3')
+
+    expect(ffmpegStub.run.calledOnce).to.be.true
+
+    expect(fsCopyFileSyncStub.calledOnce).to.be.true
+    expect(fsCopyFileSyncStub.firstCall.args[0]).to.equal('/path/to/audio/file.tmp.mp3')
+    expect(fsCopyFileSyncStub.firstCall.args[1]).to.equal('/path/to/audio/file.mp3')
+
+    expect(fsUnlinkSyncStub.calledOnce).to.be.true
+    expect(fsUnlinkSyncStub.firstCall.args[0]).to.equal('/path/to/audio/file.tmp.mp3')
+
+    // Restore the stub
+    sinon.restore()
+  })
+
+  it('should handle missing cover image', async () => {
+    // Arrange
+    coverFilePath = null
+
+    // Act
+    const result = await addCoverAndMetadataToFile(audioFilePath, coverFilePath, metadataFilePath, track, mimeType, ffmpegStub)
+
+    // Assert
+    expect(result).to.be.true
+    expect(ffmpegStub.input.calledTwice).to.be.true
+    expect(ffmpegStub.input.getCall(0).args[0]).to.equal(audioFilePath)
+    expect(ffmpegStub.input.getCall(1).args[0]).to.equal(metadataFilePath)
+
+    expect(ffmpegStub.outputOptions.callCount).to.equal(4)
+    expect(ffmpegStub.outputOptions.getCall(0).args[0]).to.deep.equal(['-map 0:a', '-map_metadata 1', '-map_metadata 0', '-map_chapters 1', '-c copy'])
+    expect(ffmpegStub.outputOptions.getCall(1).args[0]).to.deep.equal(['-metadata track=1'])
+    expect(ffmpegStub.outputOptions.getCall(2).args[0]).to.deep.equal(['-id3v2_version 3'])
+    expect(ffmpegStub.outputOptions.getCall(3).args[0]).to.deep.equal(['-map 0:v?'])
+
+    expect(ffmpegStub.output.calledOnce).to.be.true
+    expect(ffmpegStub.output.firstCall.args[0]).to.equal('/path/to/audio/file.tmp.mp3')
+
+    expect(ffmpegStub.run.calledOnce).to.be.true
+
+    expect(fsCopyFileSyncStub.calledOnce).to.be.true
+    expect(fsCopyFileSyncStub.firstCall.args[0]).to.equal('/path/to/audio/file.tmp.mp3')
+    expect(fsCopyFileSyncStub.firstCall.args[1]).to.equal('/path/to/audio/file.mp3')
+
+    expect(fsUnlinkSyncStub.calledOnce).to.be.true
+    expect(fsUnlinkSyncStub.firstCall.args[0]).to.equal('/path/to/audio/file.tmp.mp3')
+
+    // Restore the stub
+    sinon.restore()
+  })
+
+  it('should handle error during ffmpeg execution', async () => {
+    // Arrange
+    ffmpegStub.run = sinon.stub().callsFake(() => {
+      ffmpegStub.emit('error', new Error('FFmpeg error'))
+    })
+
+    // Act
+    const result = await addCoverAndMetadataToFile(audioFilePath, coverFilePath, metadataFilePath, track, mimeType, ffmpegStub)
+
+    // Assert
+    expect(result).to.be.false
+    expect(ffmpegStub.input.calledThrice).to.be.true
+    expect(ffmpegStub.input.getCall(0).args[0]).to.equal(audioFilePath)
+    expect(ffmpegStub.input.getCall(1).args[0]).to.equal(metadataFilePath)
+    expect(ffmpegStub.input.getCall(2).args[0]).to.equal(coverFilePath)
+
+    expect(ffmpegStub.outputOptions.callCount).to.equal(4)
+    expect(ffmpegStub.outputOptions.getCall(0).args[0]).to.deep.equal(['-map 0:a', '-map_metadata 1', '-map_metadata 0', '-map_chapters 1', '-c copy'])
+    expect(ffmpegStub.outputOptions.getCall(1).args[0]).to.deep.equal(['-metadata track=1'])
+    expect(ffmpegStub.outputOptions.getCall(2).args[0]).to.deep.equal(['-id3v2_version 3'])
+    expect(ffmpegStub.outputOptions.getCall(3).args[0]).to.deep.equal(['-map 2:v', '-disposition:v:0 attached_pic', '-metadata:s:v', 'title=Cover', '-metadata:s:v', 'comment=Cover'])
+
+    expect(ffmpegStub.output.calledOnce).to.be.true
+    expect(ffmpegStub.output.firstCall.args[0]).to.equal('/path/to/audio/file.tmp.mp3')
+
+    expect(ffmpegStub.run.calledOnce).to.be.true
+
+    expect(fsCopyFileSyncStub.called).to.be.false
+
+    expect(fsUnlinkSyncStub.called).to.be.false
+
+    // Restore the stub
+    sinon.restore()
+  })
+
+  it('should handle m4b embedding', async () => {
+    // Arrange
+    mimeType = 'audio/mp4'
+    audioFilePath = '/path/to/audio/file.m4b'
+
+    // Act
+    const result = await addCoverAndMetadataToFile(audioFilePath, coverFilePath, metadataFilePath, track, mimeType, ffmpegStub)
+
+    // Assert
+    expect(result).to.be.true
+    expect(ffmpegStub.input.calledThrice).to.be.true
+    expect(ffmpegStub.input.getCall(0).args[0]).to.equal(audioFilePath)
+    expect(ffmpegStub.input.getCall(1).args[0]).to.equal(metadataFilePath)
+    expect(ffmpegStub.input.getCall(2).args[0]).to.equal(coverFilePath)
+
+    expect(ffmpegStub.outputOptions.callCount).to.equal(4)
+    expect(ffmpegStub.outputOptions.getCall(0).args[0]).to.deep.equal(['-map 0:a', '-map_metadata 1', '-map_metadata 0', '-map_chapters 1', '-c copy'])
+    expect(ffmpegStub.outputOptions.getCall(1).args[0]).to.deep.equal(['-metadata track=1'])
+    expect(ffmpegStub.outputOptions.getCall(2).args[0]).to.deep.equal(['-f mp4'])
+    expect(ffmpegStub.outputOptions.getCall(3).args[0]).to.deep.equal(['-map 2:v', '-disposition:v:0 attached_pic', '-metadata:s:v', 'title=Cover', '-metadata:s:v', 'comment=Cover'])
+
+    expect(ffmpegStub.output.calledOnce).to.be.true
+    expect(ffmpegStub.output.firstCall.args[0]).to.equal('/path/to/audio/file.tmp.m4b')
+
+    expect(ffmpegStub.run.calledOnce).to.be.true
+
+    expect(fsCopyFileSyncStub.calledOnce).to.be.true
+    expect(fsCopyFileSyncStub.firstCall.args[0]).to.equal('/path/to/audio/file.tmp.m4b')
+    expect(fsCopyFileSyncStub.firstCall.args[1]).to.equal('/path/to/audio/file.m4b')
+
+    expect(fsUnlinkSyncStub.calledOnce).to.be.true
+    expect(fsUnlinkSyncStub.firstCall.args[0]).to.equal('/path/to/audio/file.tmp.m4b')
+
+    // Restore the stub
+    sinon.restore()
+  })
+})