Add concat edit timeline rendering

docs/cinematic-video-editing-service-plan.md

@@ -798,7 +798,7 @@ It writes the script only and requires an imported audio file.
 15. [x] Add strict JSON edit plan schema and validation.
 16. [x] Add `PUT /v1/edit-projects/{projectId}/plan`.
 17. [x] Add simple segment rendering without transitions.
-18. [ ] Add concat-based final timeline rendering.
+18. [x] Add concat-based final timeline rendering.
 19. [ ] Add music and voiceover audio mixing.
 20. [ ] Add render manifest with command metadata and output details.
 21. [ ] Add basic transition support: cut, crossfade, fade in, fade out.

src/main/java/org/example/videoclips/editing/FfmpegEditRenderer.java

@@ -10,6 +10,7 @@ import java.io.IOException;
 import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
 import java.nio.file.Path;
+import java.nio.file.StandardCopyOption;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Map;
@@ -51,11 +52,20 @@ public class FfmpegEditRenderer implements EditRenderer {
         createDirectory(work);
         Map<String, ClipAnalysis> clips = analysis.clips().stream()
                 .collect(Collectors.toMap(ClipAnalysis::clipId, Function.identity()));
+        List<Path> segments = new ArrayList<>();
         for (int index = 0; index < plan.decisions().size(); index++) {
             EditDecision decision = plan.decisions().get(index);
             Path output = work.resolve("segment_%04d.mp4".formatted(index + 1));
             run(segmentCommand(clips.get(decision.clipId()).sourcePath(), decision, output));
+            segments.add(output);
         }
+        Path concatFile = work.resolve("concat.txt");
+        writeConcatFile(concatFile, segments);
+        Path timeline = work.resolve("timeline-video.mp4");
+        run(concatCommand(concatFile, timeline));
+        Path output = store.projectDirectory(projectId).resolve("final.mp4");
+        copy(timeline, output);
+        projectService.updateProject(projectId, EditProjectStatus.RENDERED, Path.of(project.inputDirectory()), null);
     }
 
     List<String> segmentCommand(String source, EditDecision decision, Path output) {
@@ -76,6 +86,30 @@ public class FfmpegEditRenderer implements EditRenderer {
         return List.copyOf(command);
     }
 
+    List<String> concatCommand(Path concatFile, Path output) {
+        return List.of(properties.getFfmpegBinary(), "-hide_banner", "-y", "-f", "concat", "-safe", "0",
+                "-i", concatFile.toString(), "-c", "copy", output.toString());
+    }
+
+    private void writeConcatFile(Path file, List<Path> segments) {
+        String content = segments.stream()
+                .map(path -> "file '" + path.toAbsolutePath().toString().replace("'", "'\\''") + "'")
+                .collect(Collectors.joining(System.lineSeparator(), "", System.lineSeparator()));
+        try {
+            Files.writeString(file, content);
+        } catch (IOException ex) {
+            throw new IllegalStateException("Unable to write FFmpeg concat file", ex);
+        }
+    }
+
+    private void copy(Path source, Path target) {
+        try {
+            Files.copy(source, target, StandardCopyOption.REPLACE_EXISTING);
+        } catch (IOException ex) {
+            throw new IllegalStateException("Unable to publish final edit", ex);
+        }
+    }
+
     private void createDirectory(Path directory) {
         try {
             Files.createDirectories(directory);

src/test/java/org/example/videoclips/editing/FfmpegEditRendererTest.java

@@ -26,4 +26,16 @@ class FfmpegEditRendererTest {
         assertThat(command).containsSubsequence("-c:v", "libx264", "-c:a", "aac");
         assertThat(command).endsWith("segment.mp4");
     }
+
+    @Test
+    void buildsConcatCommandWithoutReencoding() {
+        VideoClippingProperties properties = new VideoClippingProperties();
+        FfmpegEditRenderer renderer = new FfmpegEditRenderer(properties, mock(EditProjectStore.class),
+                mock(EditProjectService.class), mock(EditPlanValidator.class), command -> null);
+
+        var command = renderer.concatCommand(Path.of("concat.txt"), Path.of("timeline-video.mp4"));
+
+        assertThat(command).containsSubsequence("-f", "concat", "-safe", "0", "-i", "concat.txt");
+        assertThat(command).containsSubsequence("-c", "copy", "timeline-video.mp4");
+    }
 }