diff --git a/doc/api/bundle.md b/doc/api/bundle.md
index b769dee..071e9ce 100644
--- a/doc/api/bundle.md
+++ b/doc/api/bundle.md
@@ -15,7 +15,7 @@ $bundle = ProBundleReader::read('path/to/presentation.probundle');
 // Access
 $bundle->getName();           // Presentation name
 $bundle->getSong();           // Song wrapper
-$bundle->getMediaFiles();     // ['path' => bytes, ...]
+$bundle->getMediaFiles();     // ['filename' => bytes, ...]
 
 // Write
 ProBundleWriter::write($bundle, 'output.probundle');
@@ -65,22 +65,22 @@ The `Song` object returned by `getSong()` has the same API as songs from `ProFil
 ## Media Files
 
 ```php
-// All media files: path => raw bytes
+// All media files: filename => raw bytes
 $mediaFiles = $bundle->getMediaFiles();
-foreach ($mediaFiles as $path => $bytes) {
-    echo "$path: " . strlen($bytes) . " bytes\n";
+foreach ($mediaFiles as $filename => $bytes) {
+    echo "$filename: " . strlen($bytes) . " bytes\n";
 }
 
 // Check if a specific media file exists
-if ($bundle->hasMediaFile('/Users/me/Downloads/Media/image.png')) {
-    $bytes = $bundle->getMediaFile('/Users/me/Downloads/Media/image.png');
+if ($bundle->hasMediaFile('background.png')) {
+    $bytes = $bundle->getMediaFile('background.png');
 }
 
 // Count
 $bundle->getMediaFileCount();  // 0, 1, 2, ...
 ```
 
-Media file paths are stored as absolute paths with a leading `/` (matching PP7 export format).
+Media files are stored as flat filenames (no directories). The writer automatically flattens any paths to `basename()`.
 
 ---
 
@@ -93,7 +93,7 @@ use ProPresenter\Parser\PresentationBundle;
 use ProPresenter\Parser\ProFileGenerator;
 use ProPresenter\Parser\ProBundleWriter;
 
-// Generate a song with a media slide
+// Generate a song with a media slide (bundleRelative for portable bundles)
 $song = ProFileGenerator::generate(
     'My Presentation',
     [
@@ -102,9 +102,10 @@ $song = ProFileGenerator::generate(
             'color' => [0.2, 0.2, 0.2, 1.0],
             'slides' => [
                 [
-                    'media' => 'file:///Users/me/Downloads/Media/background.png',
+                    'media' => 'background.png',
                     'format' => 'png',
                     'label' => 'background.png',
+                    'bundleRelative' => true,
                 ],
             ],
         ],
@@ -113,13 +114,13 @@ $song = ProFileGenerator::generate(
 );
 
 // Read the media file
-$imageBytes = file_get_contents('/Users/me/Downloads/Media/background.png');
+$imageBytes = file_get_contents('/path/to/background.png');
 
-// Create the bundle
+// Create the bundle (flat filenames)
 $bundle = new PresentationBundle(
     $song,
     'My Presentation.pro',
-    ['/Users/me/Downloads/Media/background.png' => $imageBytes],
+    ['background.png' => $imageBytes],
 );
 
 // Write to disk
@@ -128,16 +129,28 @@ ProBundleWriter::write($bundle, 'output.probundle');
 
 ### Media Path Convention
 
-Media entries use **absolute paths with a leading `/`**:
+Media entries use **flat filenames** (no directories):
 
 ```php
 $mediaFiles = [
-    '/Users/me/Downloads/Media/background.png' => $pngBytes,
-    '/Users/me/Downloads/Media/intro.mp4' => $mp4Bytes,
+    'background.png' => $pngBytes,
+    'intro.mp4' => $mp4Bytes,
 ];
 ```
 
-This matches PP7's export format. The `file:///` URL in the `.pro` protobuf maps to these paths (strip `file://` prefix).
+The writer flattens any paths to `basename()` automatically. The `.pro` protobuf uses `ROOT_CURRENT_RESOURCE` so PP7 resolves media relative to the bundle — no absolute paths needed.
+
+### `bundleRelative` Slide Option
+
+Set `'bundleRelative' => true` on media slides to use `ROOT_CURRENT_RESOURCE` instead of absolute filesystem paths:
+
+```php
+// For bundles (portable — works on any machine)
+['media' => 'image.png', 'format' => 'png', 'bundleRelative' => true]
+
+// For standalone .pro files (uses absolute path with filesystem root detection)
+['media' => 'file:///Users/me/Downloads/image.png', 'format' => 'png']
+```
 
 ---
 
@@ -151,6 +164,7 @@ ProBundleWriter::write($bundle, 'output.probundle');
 
 The writer:
 - Creates a standard ZIP archive (deflate compression)
+- **Flattens media entries to `basename()`** — no directories in the ZIP
 - Writes media entries first, `.pro` file last
 - Uses atomic write (temp file + rename) for safety
 
diff --git a/doc/formats/pp_bundle_spec.md b/doc/formats/pp_bundle_spec.md
index e1f5ede..7afbd41 100644
--- a/doc/formats/pp_bundle_spec.md
+++ b/doc/formats/pp_bundle_spec.md
@@ -19,9 +19,13 @@
 ### Container Structure
 - **Archive Type:** Standard ZIP with deflate compression (default)
 - **ZIP64 EOCD Quirk:** ProPresenter 7 exports have the same 98-byte EOCD discrepancy as `.proplaylist` files
-- **Entry Layout:**
-  - Media files at **absolute paths with leading `/`** (e.g., `/Users/me/Downloads/Media/image.png`)
+- **Entry Layout (library output — flat, portable):**
+  - Media files as **flat filenames** at ZIP root (e.g., `background.png`)
   - Single `.pro` file at root (filename only, no directory)
+  - Protobuf uses `ROOT_CURRENT_RESOURCE` to resolve media relative to the bundle
+- **Entry Layout (PP7 export — absolute paths):**
+  - Media files at **absolute paths with leading `/`** (e.g., `/Users/me/Downloads/Media/image.png`)
+  - Single `.pro` file at root
 
 ### Purpose
 A `.probundle` packages a single ProPresenter presentation (`.pro` file) together with all its referenced media assets (images, videos, audio) into a single portable archive. This enables sharing presentations between machines without losing media references.
@@ -35,22 +39,28 @@ A `.probundle` packages a single ProPresenter presentation (`.pro` file) togethe
 
 ## 2. Archive Structure
 
-### Entry Layout
+### Library Output (Flat — Portable)
 
 ```
-/Users/me/Downloads/pp-test/Media/background.png   <-- Media file (absolute path with leading /)
+background.png    <-- Media file (flat filename, no directories)
+SongName.pro      <-- Protobuf-encoded presentation
+```
+
+Media entries use **flat filenames only** (no directories, no absolute paths). The `.pro` protobuf references media via `ROOT_CURRENT_RESOURCE`, which PP7 resolves relative to the bundle. This makes bundles fully portable across machines.
+
+### PP7 Export (Absolute Paths)
+
+```
+/Users/me/Downloads/pp-test/Media/background.png   <-- Absolute path with leading /
 SongName.pro                                         <-- Protobuf-encoded presentation
 ```
 
+PP7's own exports use absolute filesystem paths as ZIP entry names. The reader handles both formats.
+
 ### Entry Order
 - **Media files first**, then the `.pro` file last
 - ProPresenter does not enforce order, but this matches PP7 export behavior
 
-### Media Entry Naming
-- Media entries use **absolute filesystem paths with a leading `/`**
-- Standard unzip tools strip the leading `/` with a warning: `warning: stripped absolute path spec from /Users/.../image.png`
-- This is intentional and matches PP7 export behavior
-
 ### Compression
 - **ProPresenter exports:** Standard deflate compression
 - **Writer output:** Standard deflate compression (ZipArchive defaults)
@@ -62,44 +72,30 @@ SongName.pro                                         <-- Protobuf-encoded presen
 
 ### Media URL Format
 
-Media references in the `.pro` protobuf must use `file:///` absolute URLs with a `LocalRelativePath` in `URL.local`.
+#### Bundle-Relative (Library Output — Portable)
 
-#### URL Structure
+For bundles, media references use `ROOT_CURRENT_RESOURCE` with just the filename. PP7 resolves this relative to the bundle itself.
 
 ```protobuf
 message URL {
-  string absolute_string = 1;       // "file:///Users/me/Downloads/Media/image.png"
-  LocalRelativePath local = 4;      // Root + relative path
+  string absolute_string = 1;       // "background.png" (just the filename)
+  LocalRelativePath local = 4;      // ROOT_CURRENT_RESOURCE + filename
   Platform platform = 5;            // PLATFORM_MACOS
 }
 ```
 
-#### LocalRelativePath
-
-```protobuf
-message LocalRelativePath {
-  Root root = 1;     // Enum mapping to macOS directory
-  string path = 2;   // Relative path from root directory
-}
+```
+URL.absolute_string = "background.png"
+URL.local.root      = ROOT_CURRENT_RESOURCE (12)
+URL.local.path      = "background.png"
+URL.platform        = PLATFORM_MACOS
 ```
 
-### Root Type Mappings
+Both `url` and `image.file.localUrl` use the same structure.
 
-| Root Enum | Value | macOS Directory |
-|-----------|-------|-----------------|
-| `ROOT_BOOT_VOLUME` | 0 | `/` (fallback) |
-| `ROOT_USER_HOME` | 2 | `~/` |
-| `ROOT_USER_DOWNLOADS` | 4 | `~/Downloads/` |
-| `ROOT_USER_DOCUMENTS` | 5 | `~/Documents/` |
-| `ROOT_USER_DESKTOP` | 6 | `~/Desktop/` |
-| `ROOT_USER_MUSIC` | 7 | `~/Music/` |
-| `ROOT_USER_PICTURES` | 8 | `~/Pictures/` |
-| `ROOT_USER_VIDEOS` | 9 | `~/Movies/` |
-| `ROOT_SHOW` | 10 | ProPresenter library directory |
+#### Absolute Paths (PP7 Export / Standalone `.pro`)
 
-### Path Construction Example
-
-For media at `file:///Users/thorsten/Downloads/pp-test/Media/background.png`:
+PP7's own exports and standalone `.pro` files use absolute `file:///` URLs with filesystem-based root mappings:
 
 ```
 URL.absolute_string = "file:///Users/thorsten/Downloads/pp-test/Media/background.png"
@@ -108,6 +104,33 @@ URL.local.path      = "pp-test/Media/background.png"
 URL.platform        = PLATFORM_MACOS
 ```
 
+#### LocalRelativePath
+
+```protobuf
+message LocalRelativePath {
+  Root root = 1;     // Enum mapping to macOS directory or bundle context
+  string path = 2;   // Relative path from root
+}
+```
+
+### Root Type Mappings
+
+| Root Enum | Value | macOS Directory |
+|-----------|-------|-----------------|
+| `ROOT_UNKNOWN` | 0 | Unknown |
+| `ROOT_BOOT_VOLUME` | 1 | `/` (fallback) |
+| `ROOT_USER_HOME` | 2 | `~/` |
+| `ROOT_USER_DOCUMENTS` | 3 | `~/Documents/` |
+| `ROOT_USER_DOWNLOADS` | 4 | `~/Downloads/` |
+| `ROOT_USER_MUSIC` | 5 | `~/Music/` |
+| `ROOT_USER_PICTURES` | 6 | `~/Pictures/` |
+| `ROOT_USER_VIDEOS` | 7 | `~/Movies/` |
+| `ROOT_USER_APP_SUPPORT` | 8 | `~/Library/Application Support/` |
+| `ROOT_SHARED` | 9 | `/Users/Shared/` |
+| `ROOT_SHOW` | 10 | ProPresenter library directory |
+| `ROOT_USER_DESKTOP` | 11 | `~/Desktop/` |
+| **`ROOT_CURRENT_RESOURCE`** | **12** | **Relative to current bundle/document** |
+
 ### Media Metadata
 
 | Field | Expected Value | Notes |
@@ -133,14 +156,15 @@ The writer produces standard ZIPs without the bug. PHP's `ZipArchive` creates cl
 
 ## 5. Differences from `.proplaylist`
 
-| Aspect | `.proplaylist` | `.probundle` |
-|--------|---------------|-------------|
-| **Purpose** | Playlist with multiple songs | Single presentation with media |
-| **Compression** | Store only (method 0) | Deflate (default) |
-| **Metadata entry** | `data` file (protobuf `rv.data.Playlist`) | None (`.pro` file IS the data) |
-| **Song entries** | Multiple `.pro` files | Single `.pro` file |
-| **Media paths** | Absolute minus leading `/` | Absolute **with** leading `/` |
-| **ZIP64** | Always ZIP64 | Standard ZIP (PP7 exports as ZIP64) |
+| Aspect | `.proplaylist` | `.probundle` (library) | `.probundle` (PP7 export) |
+|--------|---------------|----------------------|--------------------------|
+| **Purpose** | Playlist with multiple songs | Single presentation with media | Single presentation with media |
+| **Compression** | Store only (method 0) | Deflate (default) | Deflate |
+| **Metadata entry** | `data` file (protobuf `rv.data.Playlist`) | None (`.pro` file IS the data) | None |
+| **Song entries** | Multiple `.pro` files | Single `.pro` file | Single `.pro` file |
+| **Media paths** | Absolute minus leading `/` | **Flat filenames** | Absolute with leading `/` |
+| **Media URL root** | Filesystem-based roots | `ROOT_CURRENT_RESOURCE (12)` | Filesystem-based roots |
+| **ZIP64** | Always ZIP64 | Standard ZIP | ZIP64 |
 
 ---
 
@@ -151,8 +175,8 @@ The writer produces standard ZIPs without the bug. PHP's `ZipArchive` creates cl
 - **Use case:** Sharing a lyrics-only presentation.
 
 ### Multiple Media Files
-- **Valid.** Each media file gets its own ZIP entry at its absolute path.
-- **Deduplication:** Same path stored once.
+- **Valid.** Each media file gets its own ZIP entry (flat filename).
+- **Deduplication:** Same filename stored once.
 
 ### Non-Image Media
 - **Videos** (`.mp4`, `.mov`): Same URL format, different `Metadata.format`.
@@ -171,17 +195,19 @@ The writer produces standard ZIPs without the bug. PHP's `ZipArchive` creates cl
 - **RestBildExportFromPP.probundle:** Exported by PP7 after import, used as comparison reference
 
 ### Key Discoveries
-1. **Absolute paths with leading `/`:** PP7 stores media at full absolute filesystem paths in the ZIP, including the leading `/`
+1. **`ROOT_CURRENT_RESOURCE` (12) enables portable bundles:** PP7 resolves this root relative to the bundle, so media stored as flat filenames in the ZIP are found on any machine
 2. **`URL.local` is required:** PP7 cannot find media without the `LocalRelativePath` in `URL.local`
-3. **`file:///` prefix required:** `URL.absolute_string` must use the `file:///` protocol prefix
+3. **Flat filenames work:** ZIP entries like `image.png` (no directories) with `ROOT_CURRENT_RESOURCE` in the protobuf — PP7 finds the media
 4. **Lowercase format:** PP7 uses lowercase format strings (`"png"` not `"PNG"`)
-5. **Standard ZIP is fine:** PP7 imports standard deflate-compressed ZIPs without issues — the ZIP64/store/permission quirks in PP7 exports are artifacts, not requirements
+5. **Standard ZIP is fine:** PP7 imports standard deflate-compressed ZIPs without issues
 6. **ZIP64 EOCD bug:** PP7 exports have the same 98-byte offset quirk as `.proplaylist` files
+7. **PP7 exports use absolute paths:** PP7's own exports use `file:///` absolute paths — but these only work on the same machine. The library uses `ROOT_CURRENT_RESOURCE` for portability instead.
 
 ### What Didn't Work (Rejected Approaches)
-- **Relative media paths:** PP7 cannot resolve `Media/image.png` — needs absolute paths
+- **`file:///filename.png` with `ROOT_BOOT_VOLUME`:** PP7 cannot resolve bare filenames with filesystem roots
+- **`file:///Users/.../filename.png` with flat ZIP entry:** PP7 needs the URL root to match the ZIP structure
+- **`ROOT_SHOW` with bare filename:** PP7 looks in its library dir, not the bundle
 - **Missing `URL.local`:** PP7 shows "image not found" without `LocalRelativePath`
-- **Missing `file:///`:** Plain paths like `/Users/me/image.png` are not recognized
 - **Uppercase format:** `"PNG"` works but doesn't match PP7's own output
 - **Forced store compression / 000 permissions:** Unnecessary hacks that don't affect import
 
diff --git a/php/bin/regen-test-bundles.php b/php/bin/regen-test-bundles.php
index 7894cfe..842aff1 100644
--- a/php/bin/regen-test-bundles.php
+++ b/php/bin/regen-test-bundles.php
@@ -17,7 +17,6 @@ $imageBytes = file_get_contents($tmpPng);
 unlink($tmpPng);
 
 $refDir = dirname(__DIR__, 2) . '/ref';
-$mediaAbsPath = '/Users/thorsten/AI/propresenter/ref/Media/test-background.png';
 
 $song = ProFileGenerator::generate(
     'TestBild',
@@ -27,8 +26,10 @@ $song = ProFileGenerator::generate(
             'color' => [0.0, 0.0, 0.0, 1.0],
             'slides' => [
                 [
-                    'media' => 'file://' . $mediaAbsPath,
+                    'media' => 'test-background.png',
                     'format' => 'png',
+                    'label' => 'test-background.png',
+                    'bundleRelative' => true,
                 ],
             ],
         ],
@@ -36,6 +37,6 @@ $song = ProFileGenerator::generate(
     [['name' => 'normal', 'groupNames' => ['Verse 1']]],
 );
 
-$bundle = new PresentationBundle($song, 'TestBild.pro', [$mediaAbsPath => $imageBytes]);
+$bundle = new PresentationBundle($song, 'TestBild.pro', ['test-background.png' => $imageBytes]);
 ProBundleWriter::write($bundle, $refDir . '/TestBild.probundle');
 echo "TestBild.probundle written\n";
diff --git a/php/src/PresentationBundle.php b/php/src/PresentationBundle.php
index 4c6ce24..9d1dbe8 100644
--- a/php/src/PresentationBundle.php
+++ b/php/src/PresentationBundle.php
@@ -13,16 +13,16 @@ use Rv\Data\Presentation;
  * together with all its referenced media assets (images, videos, audio).
  * This is the Pro7 successor to the Pro6 .pro6x format.
  *
- * Archive layout:
+ * Archive layout (flat — no directories):
+ *   image.jpg             ← Media files (basename only)
+ *   video.mp4
  *   SongName.pro          ← Protobuf-encoded presentation
- *   Media/image.jpg       ← Referenced media files
- *   Media/video.mp4
  */
 class PresentationBundle
 {
     private Song $song;
 
-    /** @var array<string, string> relative path => raw bytes */
+    /** @var array<string, string> filename => raw bytes */
     private array $mediaFiles;
 
     private string $proFilename;
@@ -74,7 +74,7 @@ class PresentationBundle
     /**
      * All media files in the bundle.
      *
-     * @return array<string, string> relative path => raw bytes
+     * @return array<string, string> filename => raw bytes
      */
     public function getMediaFiles(): array
     {
diff --git a/php/src/ProBundleWriter.php b/php/src/ProBundleWriter.php
index d9ce66f..a3075c3 100644
--- a/php/src/ProBundleWriter.php
+++ b/php/src/ProBundleWriter.php
@@ -33,7 +33,7 @@ final class ProBundleWriter
             $isOpen = true;
 
             foreach ($bundle->getMediaFiles() as $entryName => $contents) {
-                self::addEntry($zip, $entryName, $contents, $filePath);
+                self::addEntry($zip, basename($entryName), $contents, $filePath);
             }
 
             $proBytes = $bundle->getPresentation()->serializeToString();
diff --git a/php/src/ProFileGenerator.php b/php/src/ProFileGenerator.php
index cd579ff..d2b462d 100644
--- a/php/src/ProFileGenerator.php
+++ b/php/src/ProFileGenerator.php
@@ -228,6 +228,7 @@ final class ProFileGenerator
                 $mediaName,
                 (int) ($slideData['mediaWidth'] ?? 0),
                 (int) ($slideData['mediaHeight'] ?? 0),
+                (bool) ($slideData['bundleRelative'] ?? false),
             );
         }
 
@@ -281,17 +282,27 @@ final class ProFileGenerator
         return $action;
     }
 
-    private static function buildMediaAction(string $absoluteUrl, string $format, ?string $name = null, int $imageWidth = 0, int $imageHeight = 0): Action
+    private static function buildMediaAction(string $absoluteUrl, string $format, ?string $name = null, int $imageWidth = 0, int $imageHeight = 0, bool $bundleRelative = false): Action
     {
-        $url = new URL();
-        $url->setAbsoluteString($absoluteUrl);
-        $url->setLocal(self::buildLocalRelativePath($absoluteUrl));
-        $url->setPlatform(UrlPlatform::PLATFORM_MACOS);
+        if ($bundleRelative) {
+            $filename = basename($absoluteUrl);
+            $url = self::buildBundleRelativeUrl($filename);
+            $fileLocalUrl = self::buildBundleRelativeUrl($filename);
+        } else {
+            $url = new URL();
+            $url->setAbsoluteString($absoluteUrl);
+            $url->setLocal(self::buildLocalRelativePath($absoluteUrl));
+            $url->setPlatform(UrlPlatform::PLATFORM_MACOS);
+
+            $fileLocalUrl = new URL();
+            $fileLocalUrl->setAbsoluteString($absoluteUrl);
+            $fileLocalUrl->setLocal(self::buildLocalRelativePath($absoluteUrl));
+            $fileLocalUrl->setPlatform(UrlPlatform::PLATFORM_MACOS);
+        }
 
         $metadata = new Metadata();
         $metadata->setFormat($format);
 
-        // Build the image type properties with drawing + file
         $naturalSize = new Size();
         $naturalSize->setWidth($imageWidth);
         $naturalSize->setHeight($imageHeight);
@@ -310,11 +321,6 @@ final class ProFileGenerator
         $drawing->setCropInsets($cropInsets);
         $drawing->setAlphaType(AlphaType::ALPHA_TYPE_STRAIGHT);
 
-        $fileLocalUrl = new URL();
-        $fileLocalUrl->setAbsoluteString($absoluteUrl);
-        $fileLocalUrl->setLocal(self::buildLocalRelativePath($absoluteUrl));
-        $fileLocalUrl->setPlatform(UrlPlatform::PLATFORM_MACOS);
-
         $fileProperties = new FileProperties();
         $fileProperties->setLocalUrl($fileLocalUrl);
 
@@ -346,6 +352,20 @@ final class ProFileGenerator
         return $action;
     }
 
+    private static function buildBundleRelativeUrl(string $filename): URL
+    {
+        $local = new LocalRelativePath();
+        $local->setRoot(LocalRelativePath\Root::ROOT_CURRENT_RESOURCE);
+        $local->setPath($filename);
+
+        $url = new URL();
+        $url->setAbsoluteString($filename);
+        $url->setLocal($local);
+        $url->setPlatform(UrlPlatform::PLATFORM_MACOS);
+
+        return $url;
+    }
+
     private static function buildSlideElement(string $name, string $text, ?Rect $bounds = null): SlideElement
     {
         $graphicsElement = new GraphicsElement();
diff --git a/php/tests/ProBundleTest.php b/php/tests/ProBundleTest.php
index 4dc6752..5459eac 100644
--- a/php/tests/ProBundleTest.php
+++ b/php/tests/ProBundleTest.php
@@ -105,7 +105,7 @@ class ProBundleTest extends TestCase
         $bundle = new PresentationBundle(
             $song,
             'Bundle Test Song.pro',
-            ['Media/test-background.png' => $imageBytes],
+            ['test-background.png' => $imageBytes],
         );
 
         $bundlePath = $this->tmpDir . '/BundleTestSong.probundle';
@@ -117,7 +117,7 @@ class ProBundleTest extends TestCase
         $zip = new ZipArchive();
         $this->assertTrue($zip->open($bundlePath) === true);
         $this->assertNotFalse($zip->locateName('Bundle Test Song.pro'));
-        $this->assertNotFalse($zip->locateName('Media/test-background.png'));
+        $this->assertNotFalse($zip->locateName('test-background.png'));
         $this->assertSame(2, $zip->numFiles);
         $zip->close();
 
@@ -126,8 +126,8 @@ class ProBundleTest extends TestCase
         $this->assertSame('Bundle Test Song', $readBundle->getName());
         $this->assertSame('Bundle Test Song.pro', $readBundle->getProFilename());
         $this->assertSame(1, $readBundle->getMediaFileCount());
-        $this->assertTrue($readBundle->hasMediaFile('Media/test-background.png'));
-        $this->assertSame($imageBytes, $readBundle->getMediaFile('Media/test-background.png'));
+        $this->assertTrue($readBundle->hasMediaFile('test-background.png'));
+        $this->assertSame($imageBytes, $readBundle->getMediaFile('test-background.png'));
 
         $readSong = $readBundle->getSong();
         $this->assertSame('Bundle Test Song', $readSong->getName());
@@ -168,8 +168,8 @@ class ProBundleTest extends TestCase
             $song,
             'Multi Media Song.pro',
             [
-                'Media/slide1.png' => $image1Bytes,
-                'Media/slide2.png' => $image2Bytes,
+                'slide1.png' => $image1Bytes,
+                'slide2.png' => $image2Bytes,
             ],
         );
 
@@ -179,10 +179,10 @@ class ProBundleTest extends TestCase
         $readBundle = ProBundleReader::read($bundlePath);
 
         $this->assertSame(2, $readBundle->getMediaFileCount());
-        $this->assertTrue($readBundle->hasMediaFile('Media/slide1.png'));
-        $this->assertTrue($readBundle->hasMediaFile('Media/slide2.png'));
-        $this->assertSame($image1Bytes, $readBundle->getMediaFile('Media/slide1.png'));
-        $this->assertSame($image2Bytes, $readBundle->getMediaFile('Media/slide2.png'));
+        $this->assertTrue($readBundle->hasMediaFile('slide1.png'));
+        $this->assertTrue($readBundle->hasMediaFile('slide2.png'));
+        $this->assertSame($image1Bytes, $readBundle->getMediaFile('slide1.png'));
+        $this->assertSame($image2Bytes, $readBundle->getMediaFile('slide2.png'));
     }
 
     #[Test]
@@ -238,15 +238,13 @@ class ProBundleTest extends TestCase
     }
 
     #[Test]
-    public function writeProducesStandardZipWithAbsoluteMediaPaths(): void
+    public function writeProducesStandardZipWithFlatMediaPaths(): void
     {
         $imagePath = $this->tmpDir . '/bg.png';
         $this->createTestPngImage($imagePath, 100, 100);
         $imageBytes = file_get_contents($imagePath);
         $this->assertNotFalse($imageBytes);
 
-        $mediaAbsPath = '/Users/test/Media/bg.png';
-
         $song = ProFileGenerator::generate(
             'ZipFormatTest',
             [
@@ -255,8 +253,9 @@ class ProBundleTest extends TestCase
                     'color' => [0, 0, 0, 1],
                     'slides' => [
                         [
-                            'media' => 'file://' . $mediaAbsPath,
+                            'media' => 'bg.png',
                             'format' => 'png',
+                            'bundleRelative' => true,
                         ],
                     ],
                 ],
@@ -267,7 +266,7 @@ class ProBundleTest extends TestCase
         $bundle = new PresentationBundle(
             $song,
             'ZipFormatTest.pro',
-            [$mediaAbsPath => $imageBytes],
+            ['bg.png' => $imageBytes],
         );
 
         $bundlePath = $this->tmpDir . '/ZipFormatTest.probundle';
@@ -277,8 +276,8 @@ class ProBundleTest extends TestCase
         $this->assertTrue($zip->open($bundlePath) === true);
         $this->assertSame(2, $zip->numFiles);
 
-        $mediaIdx = $zip->locateName($mediaAbsPath);
-        $this->assertNotFalse($mediaIdx, 'Media entry should use absolute path with leading /');
+        $mediaIdx = $zip->locateName('bg.png');
+        $this->assertNotFalse($mediaIdx, 'Media entry should use flat filename');
 
         $proIdx = $zip->locateName('ZipFormatTest.pro');
         $this->assertNotFalse($proIdx);
@@ -288,8 +287,8 @@ class ProBundleTest extends TestCase
 
         $readBundle = ProBundleReader::read($bundlePath);
         $this->assertSame('ZipFormatTest', $readBundle->getName());
-        $this->assertTrue($readBundle->hasMediaFile($mediaAbsPath));
-        $this->assertSame($imageBytes, $readBundle->getMediaFile($mediaAbsPath));
+        $this->assertTrue($readBundle->hasMediaFile('bg.png'));
+        $this->assertSame($imageBytes, $readBundle->getMediaFile('bg.png'));
     }
 
     #[Test]
@@ -310,7 +309,7 @@ class ProBundleTest extends TestCase
         $bundle = new PresentationBundle(
             $song,
             'Wrapper Test.pro',
-            ['Media/bg.jpg' => 'fake-jpeg-bytes'],
+            ['bg.jpg' => 'fake-jpeg-bytes'],
         );
 
         $this->assertSame('Wrapper Test', $bundle->getName());
@@ -318,9 +317,9 @@ class ProBundleTest extends TestCase
         $this->assertSame($song, $bundle->getSong());
         $this->assertSame($song->getPresentation(), $bundle->getPresentation());
         $this->assertSame(1, $bundle->getMediaFileCount());
-        $this->assertTrue($bundle->hasMediaFile('Media/bg.jpg'));
-        $this->assertSame('fake-jpeg-bytes', $bundle->getMediaFile('Media/bg.jpg'));
-        $this->assertSame(['Media/bg.jpg' => 'fake-jpeg-bytes'], $bundle->getMediaFiles());
+        $this->assertTrue($bundle->hasMediaFile('bg.jpg'));
+        $this->assertSame('fake-jpeg-bytes', $bundle->getMediaFile('bg.jpg'));
+        $this->assertSame(['bg.jpg' => 'fake-jpeg-bytes'], $bundle->getMediaFiles());
     }
 
     private function createTestPngImage(string $path, int $width, int $height): void
diff --git a/php/tests/ProFileGeneratorTest.php b/php/tests/ProFileGeneratorTest.php
index 7671d97..ba48bd1 100644
--- a/php/tests/ProFileGeneratorTest.php
+++ b/php/tests/ProFileGeneratorTest.php
@@ -1133,7 +1133,7 @@ class ProFileGeneratorTest extends TestCase
         $bundle = new PresentationBundle(
             $song,
             'TestBild.pro',
-            ['Media/test-background.png' => $fakeImageBytes],
+            ['test-background.png' => $fakeImageBytes],
         );
 
         $path = $this->tmpDir . '/TestBild.probundle';
@@ -1145,7 +1145,7 @@ class ProFileGeneratorTest extends TestCase
         $this->assertSame('TestBild', $read->getName());
         $this->assertSame('TestBild.pro', $read->getProFilename());
         $this->assertSame(1, $read->getMediaFileCount());
-        $this->assertTrue($read->hasMediaFile('Media/test-background.png'));
+        $this->assertTrue($read->hasMediaFile('test-background.png'));
 
         // UUID preserved through serialization
         $this->assertSame(
diff --git a/ref/TestBild.probundle b/ref/TestBild.probundle
index bfcf631..ead643b 100644
Binary files a/ref/TestBild.probundle and b/ref/TestBild.probundle differ