Add basic edit transitions

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

@@ -801,7 +801,7 @@ It writes the script only and requires an imported audio file.
 18. [x] Add concat-based final timeline rendering.
 19. [x] Add music and voiceover audio mixing.
 20. [x] Add render manifest with command metadata and output details.
-21. [ ] Add basic transition support: cut, crossfade, fade in, fade out.
+21. [x] Add basic transition support: cut, crossfade, fade in, fade out.
 22. [ ] Add SFX cue support.
 23. [ ] Add optional generated voiceover adapter interface.
 24. [ ] Add structured logs and metrics for analysis, planning, and rendering durations.

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

@@ -84,15 +84,26 @@ public class FfmpegEditRenderer implements EditRenderer {
     }
 
     List<String> segmentCommand(String source, EditDecision decision, Path output) {
-        String filter = "scale=%d:%d:force_original_aspect_ratio=decrease,".formatted(
+        double outputDuration = (decision.sourceEndSeconds() - decision.sourceStartSeconds()) / decision.playbackSpeed();
+        StringBuilder filter = new StringBuilder("scale=%d:%d:force_original_aspect_ratio=decrease,".formatted(
                 properties.getOutputWidth(), properties.getOutputHeight())
                 + "pad=%d:%d:(ow-iw)/2:(oh-ih)/2,format=yuv420p".formatted(
-                properties.getOutputWidth(), properties.getOutputHeight());
+                properties.getOutputWidth(), properties.getOutputHeight()));
+        filter.append(",setpts=PTS/").append(decision.playbackSpeed());
+        double fadeDuration = Math.min(0.5, outputDuration / 2);
+        if ("fade-in".equals(decision.transitionIn()) || "crossfade".equals(decision.transitionIn())) {
+            filter.append(",fade=t=in:st=0:d=").append(fadeDuration);
+        }
+        if ("fade-out".equals(decision.transitionOut()) || "crossfade".equals(decision.transitionOut())) {
+            filter.append(",fade=t=out:st=").append(Math.max(0, outputDuration - fadeDuration))
+                    .append(":d=").append(fadeDuration);
+        }
         List<String> command = new ArrayList<>(List.of(
                 properties.getFfmpegBinary(), "-hide_banner", "-y",
                 "-ss", Double.toString(decision.sourceStartSeconds()),
                 "-to", Double.toString(decision.sourceEndSeconds()),
-                "-i", source, "-vf", filter,
+                "-i", source, "-vf", filter.toString(),
+                "-af", "atempo=" + decision.playbackSpeed(),
                 "-r", Integer.toString(properties.getOutputFrameRate()),
                 "-map", "0:v:0", "-map", "0:a?",
                 "-c:v", "libx264", "-preset", "veryfast", "-crf", "18",

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

@@ -21,8 +21,9 @@ class FfmpegEditRendererTest {
         var command = renderer.segmentCommand("source.mp4", decision, Path.of("segment.mp4"));
 
         assertThat(command).containsSubsequence("-ss", "1.25", "-to", "5.5", "-i", "source.mp4");
-        assertThat(command).contains("scale=1920:1080:force_original_aspect_ratio=decrease,"
+        assertThat(command).anyMatch(argument -> argument.startsWith(
-                + "pad=1920:1080:(ow-iw)/2:(oh-ih)/2,format=yuv420p");
+                "scale=1920:1080:force_original_aspect_ratio=decrease,"
+                        + "pad=1920:1080:(ow-iw)/2:(oh-ih)/2,format=yuv420p"));
         assertThat(command).containsSubsequence("-c:v", "libx264", "-c:a", "aac");
         assertThat(command).endsWith("segment.mp4");
     }
@@ -53,4 +54,20 @@ class FfmpegEditRendererTest {
                 + "[0:a][music][voice]amix=inputs=3:duration=first:dropout_transition=2[a]");
         assertThat(command).containsSubsequence("-c:v", "copy", "-c:a", "aac");
     }
+
+    @Test
+    void appliesFadeAndPlaybackTreatmentsToSegments() {
+        VideoClippingProperties properties = new VideoClippingProperties();
+        FfmpegEditRenderer renderer = new FfmpegEditRenderer(properties, mock(EditProjectStore.class),
+                mock(EditProjectService.class), mock(EditPlanValidator.class), command -> null);
+        EditDecision decision = new EditDecision("clip-1", 0, 4, 0, 2,
+                "fade-in", "crossfade", 2, "grade", "reason");
+
+        var command = renderer.segmentCommand("source.mp4", decision, Path.of("segment.mp4"));
+
+        assertThat(command).contains("scale=1920:1080:force_original_aspect_ratio=decrease,"
+                + "pad=1920:1080:(ow-iw)/2:(oh-ih)/2,format=yuv420p,setpts=PTS/2.0,"
+                + "fade=t=in:st=0:d=0.5,fade=t=out:st=1.5:d=0.5");
+        assertThat(command).containsSubsequence("-af", "atempo=2.0");
+    }
 }