fix: resolve compositor crash for H.264 MP4 files with container duration issues

CHANGELOG.md

@@ -1,3 +1,6 @@
+## 1.16.1
+- **FIX**(iOS, macOS): Fix crash `No source tracks available for compositing` when rendering H.264 MP4 files whose container duration slightly exceeds the video track's actual frame duration. The compositor time range is now clamped to the video track's real `timeRange` before inserting into the composition, preventing AVFoundation from requesting frames that have no pixel buffer. A black-frame fallback was also added as a safety net.
+
 ## 1.16.0
 - **FEAT**(android, iOS, macOS): Add per-clip `playbackSpeed` to `VideoSegment`, allowing each segment in a multi-clip composition to have its own playback speed (e.g. `2.0` for fast-forward, `0.5` for slow-motion).
 - **DEPRECATED**: `VideoRenderData.playbackSpeed` is deprecated. Use `VideoSegment.playbackSpeed` instead.

example/integration_test/video_render_test.dart

@@ -1800,4 +1800,82 @@ void main() {
       );
     }, skip: true);
   });
+
+  // ===========================================================================
+  // Regression Tests
+  // ===========================================================================
+  group('Regression tests', () {
+    // Issue #131 – reported by @rabble
+    // Certain H.264 MP4 files have a container duration that is slightly longer
+    // than the video track's actual decoded frames. This caused AVFoundation to
+    // call the custom compositor for a time slot where no pixel buffer was
+    // available (sourceTrackIDs empty), resulting in the crash:
+    //   PlatformException(RENDER_ERROR,
+    //     No source tracks available for compositing
+    // (sourceTrackIDs: 0, configTrackID: 1))
+    // Fix: clamp ClipInstruction.timeRange to the video track's actual
+    // timeRange in VideoSequenceBuilder before inserting into the composition.
+    group('#131 – H.264 MP4 with container duration > track duration', () {
+      final divineVideo = EditorVideo.asset(kVideoEditorExampleDivinePath);
+
+      testWidgets('plain export succeeds (no effects)', (_) async {
+        final result = await ProVideoEditor.instance.renderVideo(
+          VideoRenderData(
+            videoSegments: [VideoSegment(video: divineVideo)],
+            outputFormat: VideoOutputFormat.mp4,
+            shouldOptimizeForNetworkUse: true,
+          ),
+        );
+        expect(result.lengthInBytes, greaterThan(10000));
+      }, skip: !isIOS && !isMacOS);
+
+      testWidgets(
+        'export with image layer (original crash scenario)',
+        (_) async {
+          final watermark = await createTestOverlayImage(
+            width: 200,
+            height: 100,
+          );
+          final result = await ProVideoEditor.instance.renderVideo(
+            VideoRenderData(
+              videoSegments: [VideoSegment(video: divineVideo)],
+              outputFormat: VideoOutputFormat.mp4,
+              shouldOptimizeForNetworkUse: true,
+              imageLayers: [
+                ImageLayer(image: EditorLayerImage.memory(watermark)),
+              ],
+            ),
+          );
+          expect(result.lengthInBytes, greaterThan(10000));
+        },
+        skip: !isIOS && !isMacOS,
+      );
+
+      testWidgets('export with color filter + image layer', (_) async {
+        final watermark = await createTestOverlayImage(width: 200, height: 100);
+        final result = await ProVideoEditor.instance.renderVideo(
+          VideoRenderData(
+            videoSegments: [VideoSegment(video: divineVideo)],
+            outputFormat: VideoOutputFormat.mp4,
+            colorFilters: kBasicFilterMatrix,
+            imageLayers: [
+              ImageLayer(image: EditorLayerImage.memory(watermark)),
+            ],
+          ),
+        );
+        expect(result.lengthInBytes, greaterThan(10000));
+      }, skip: !isIOS && !isMacOS);
+
+      testWidgets('export with blur', (_) async {
+        final result = await ProVideoEditor.instance.renderVideo(
+          VideoRenderData(
+            videoSegments: [VideoSegment(video: divineVideo)],
+            outputFormat: VideoOutputFormat.mp4,
+            blur: 3,
+          ),
+        );
+        expect(result.lengthInBytes, greaterThan(10000));
+      }, skip: !isIOS && !isMacOS);
+    });
+  });
 }

example/lib/core/constants/example_constants.dart

@@ -10,6 +10,12 @@ const String kVideoEditorExampleH264Path = 'assets/demo.mp4';
 /// examples.
 const String kVideoEditorExampleAssetWorldPath = 'assets/demo_world.mp4';
 
+/// A local path to a H.264 MP4 where the container duration slightly exceeds
+/// the video track's actual frame duration. Used to reproduce issue #131
+/// (compositor crash: "No source tracks available") reported by @rabble.
+const String kVideoEditorExampleDivinePath =
+    'assets/tests/divine_transcribed.mp4';
+
 /// A local path to the first example audio track used in video editor demos.
 const String kVideoEditorExampleAudio1Path = 'assets/audio1.mp3';
 

ios/Classes/src/features/render/helpers/VideoSequenceBuilder.swift

@@ -173,7 +173,22 @@ internal class VideoSequenceBuilder {
             }
 
             // Calculate time range for this clip
-            let clipTimeRange = await calculateTimeRange(for: clip, from: asset)
+            let rawClipTimeRange = await calculateTimeRange(for: clip, from: asset)
+
+            // Clamp clip range to the video track's actual available range.
+            // Some MP4 files have a container duration slightly longer than the video
+            // track's decoded frames. Without clamping, insertTimeRange silently truncates
+            // the insert but the ClipInstruction keeps the longer duration, creating a gap
+            // where AVFoundation calls the compositor with no source frame available
+            // (sourceTrackIDs empty), causing a RENDER_ERROR crash.
+            let videoTrackTimeRange: CMTimeRange
+            if #available(iOS 15.0, *) {
+                videoTrackTimeRange = (try? await videoTrack.load(.timeRange)) ?? videoTrack.timeRange
+            } else {
+                videoTrackTimeRange = videoTrack.timeRange
+            }
+            let clampedRange = CMTimeRangeGetIntersection(rawClipTimeRange, otherRange: videoTrackTimeRange)
+            let clipTimeRange = clampedRange.duration > .zero ? clampedRange : rawClipTimeRange
             let clipDuration = clipTimeRange.duration
             let insertStart = totalDuration
 

ios/Classes/src/features/render/utils/VideoCompositor.swift

@@ -175,7 +175,11 @@ class VideoCompositor: NSObject, AVVideoCompositing {
         kCVPixelBufferPixelFormatTypeKey as String: Int(kCVPixelFormatType_32BGRA)
     ]
 
-    func renderContextChanged(_ newRenderContext: AVVideoCompositionRenderContext) {}
+    private var renderContext: AVVideoCompositionRenderContext?
+
+    func renderContextChanged(_ newRenderContext: AVVideoCompositionRenderContext) {
+        renderContext = newRenderContext
+    }
 
     func startRequest(_ request: AVAsynchronousVideoCompositionRequest) {
         // Try to get source buffer from the first available track
@@ -205,13 +209,26 @@ class VideoCompositor: NSObject, AVVideoCompositing {
         }
 
         guard let sourceBuffer = sourceBuffer else {
-            request.finish(
-                with: NSError(
-                    domain: "VideoCompositor", code: 0,
-                    userInfo: [
-                        NSLocalizedDescriptionKey:
-                            "No source tracks available for compositing (sourceTrackIDs: \(request.sourceTrackIDs.count), configTrackID: \(sourceTrackID))"
-                    ]))
+            // Last-resort fallback: output a black frame rather than aborting the entire render.
+            // This can happen for certain MP4 files where the container duration slightly exceeds
+            // the video track's actual decoded frames, causing AVFoundation to call the compositor
+            // for a time slot where no pixel buffer is available.
+            if let ctx = renderContext, let blackBuffer = ctx.newPixelBuffer() {
+                CVPixelBufferLockBaseAddress(blackBuffer, [])
+                if let addr = CVPixelBufferGetBaseAddress(blackBuffer) {
+                    memset(addr, 0, CVPixelBufferGetDataSize(blackBuffer))
+                }
+                CVPixelBufferUnlockBaseAddress(blackBuffer, [])
+                request.finish(withComposedVideoFrame: blackBuffer)
+            } else {
+                request.finish(
+                    with: NSError(
+                        domain: "VideoCompositor", code: 0,
+                        userInfo: [
+                            NSLocalizedDescriptionKey:
+                                "No source tracks available for compositing (sourceTrackIDs: \(request.sourceTrackIDs.count), configTrackID: \(sourceTrackID))"
+                        ]))
+            }
             return
         }
         var outputImage = CIImage(cvPixelBuffer: sourceBuffer)

macos/Classes/src/features/render/helpers/VideoSequenceBuilder.swift

@@ -173,7 +173,17 @@ internal class VideoSequenceBuilder {
             }
 
             // Calculate time range for this clip
-            let clipTimeRange = await calculateTimeRange(for: clip, from: asset)
+            let rawClipTimeRange = await calculateTimeRange(for: clip, from: asset)
+
+            // Clamp clip range to the video track's actual available range.
+            // Some MP4 files have a container duration slightly longer than the video
+            // track's decoded frames. Without clamping, insertTimeRange silently truncates
+            // the insert but the ClipInstruction keeps the longer duration, creating a gap
+            // where AVFoundation calls the compositor with no source frame available
+            // (sourceTrackIDs empty), causing a RENDER_ERROR crash.
+            let videoTrackTimeRange = videoTrack.timeRange
+            let clampedRange = CMTimeRangeGetIntersection(rawClipTimeRange, otherRange: videoTrackTimeRange)
+            let clipTimeRange = clampedRange.duration > .zero ? clampedRange : rawClipTimeRange
             let clipDuration = clipTimeRange.duration
             let insertStart = totalDuration
 

macos/Classes/src/features/render/utils/VideoCompositor.swift

@@ -173,7 +173,11 @@ class VideoCompositor: NSObject, AVVideoCompositing {
         kCVPixelBufferPixelFormatTypeKey as String: Int(kCVPixelFormatType_32BGRA)
     ]
 
-    func renderContextChanged(_ newRenderContext: AVVideoCompositionRenderContext) {}
+    private var renderContext: AVVideoCompositionRenderContext?
+
+    func renderContextChanged(_ newRenderContext: AVVideoCompositionRenderContext) {
+        renderContext = newRenderContext
+    }
 
     func startRequest(_ request: AVAsynchronousVideoCompositionRequest) {
         // Try to get source buffer from the first available track
@@ -203,13 +207,26 @@ class VideoCompositor: NSObject, AVVideoCompositing {
         }
 
         guard let sourceBuffer = sourceBuffer else {
-            request.finish(
-                with: NSError(
-                    domain: "VideoCompositor", code: 0,
-                    userInfo: [
-                        NSLocalizedDescriptionKey:
-                            "No source tracks available for compositing (sourceTrackIDs: \(request.sourceTrackIDs.count), configTrackID: \(sourceTrackID))"
-                    ]))
+            // Last-resort fallback: output a black frame rather than aborting the entire render.
+            // This can happen for certain MP4 files where the container duration slightly exceeds
+            // the video track's actual decoded frames, causing AVFoundation to call the compositor
+            // for a time slot where no pixel buffer is available.
+            if let ctx = renderContext, let blackBuffer = ctx.newPixelBuffer() {
+                CVPixelBufferLockBaseAddress(blackBuffer, [])
+                if let addr = CVPixelBufferGetBaseAddress(blackBuffer) {
+                    memset(addr, 0, CVPixelBufferGetDataSize(blackBuffer))
+                }
+                CVPixelBufferUnlockBaseAddress(blackBuffer, [])
+                request.finish(withComposedVideoFrame: blackBuffer)
+            } else {
+                request.finish(
+                    with: NSError(
+                        domain: "VideoCompositor", code: 0,
+                        userInfo: [
+                            NSLocalizedDescriptionKey:
+                                "No source tracks available for compositing (sourceTrackIDs: \(request.sourceTrackIDs.count), configTrackID: \(sourceTrackID))"
+                        ]))
+            }
             return
         }
         var outputImage = CIImage(cvPixelBuffer: sourceBuffer)

pubspec.yaml

@@ -1,6 +1,6 @@
 name: pro_video_editor
 description: "A Flutter video editor: Seamlessly enhance your videos with user-friendly editing features."
-version: 1.16.0
+version: 1.16.1
 homepage: https://github.com/hm21/pro_video_editor/
 repository: https://github.com/hm21/pro_video_editor/
 documentation: https://github.com/hm21/pro_video_editor/