Add cinematic contact sheet generation

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

@@ -788,7 +788,7 @@ It writes the script only and requires an imported audio file.
 5. [x] Add clip discovery for project input directories.
 6. [x] Add `ffprobe` analysis and validation for all input clips.
 7. [x] Add thumbnail extraction.
-8. [ ] Add contact sheet generation.
+8. [x] Add contact sheet generation.
 9. [ ] Add optional proxy generation.
 10. [ ] Add `analysis.json` writing and reading.
 11. [ ] Add storyboard prompt generation from `analysis.json`.

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

@@ -0,0 +1,75 @@
+package org.example.videoclips.editing;
+
+import org.example.videoclips.config.VideoClippingProperties;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
+import org.springframework.stereotype.Component;
+
+import java.io.IOException;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.List;
+
+@Component
+@ConditionalOnProperty(name = "video-clipping.editing.enabled", havingValue = "true", matchIfMissing = true)
+public class ContactSheetGenerator {
+
+    private final VideoClippingProperties.Editing properties;
+    private final ProcessExecutor processExecutor;
+
+    @Autowired
+    public ContactSheetGenerator(VideoClippingProperties properties) {
+        this(properties, ContactSheetGenerator::execute);
+    }
+
+    ContactSheetGenerator(VideoClippingProperties properties, ProcessExecutor processExecutor) {
+        this.properties = properties.getEditing();
+        this.processExecutor = processExecutor;
+    }
+
+    public String generate(ClipAnalysis clip, Path contactSheetDirectory) {
+        try {
+            Files.createDirectories(contactSheetDirectory);
+        } catch (IOException ex) {
+            throw new IllegalStateException("Unable to create contact sheet directory", ex);
+        }
+        Path output = contactSheetDirectory.resolve(clip.clipId() + ".jpg");
+        int columns = Math.max(1, properties.getContactSheetColumns());
+        List<String> command = List.of(
+                properties.getFfmpegBinary(),
+                "-hide_banner", "-y",
+                "-i", clip.sourcePath(),
+                "-vf", "fps=1/2,scale=320:-1,tile=%dx%d".formatted(columns, columns),
+                "-frames:v", "1",
+                output.toString()
+        );
+        ProcessResult result;
+        try {
+            result = processExecutor.execute(command);
+        } catch (InterruptedException ex) {
+            Thread.currentThread().interrupt();
+            throw new IllegalStateException("Interrupted while generating contact sheet", ex);
+        } catch (IOException ex) {
+            throw new IllegalStateException("Unable to run FFmpeg for contact sheet generation", ex);
+        }
+        if (result.exitCode() != 0) {
+            throw new IllegalStateException("FFmpeg contact sheet generation exited with code " + result.exitCode());
+        }
+        return output.toString();
+    }
+
+    private static ProcessResult execute(List<String> command) throws IOException, InterruptedException {
+        Process process = new ProcessBuilder(command).redirectErrorStream(true).start();
+        String output = new String(process.getInputStream().readAllBytes(), StandardCharsets.UTF_8);
+        return new ProcessResult(process.waitFor(), output);
+    }
+
+    record ProcessResult(int exitCode, String output) {
+    }
+
+    @FunctionalInterface
+    interface ProcessExecutor {
+        ProcessResult execute(List<String> command) throws IOException, InterruptedException;
+    }
+}

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

@@ -0,0 +1,88 @@
+package org.example.videoclips.editing;
+
+import org.example.videoclips.config.VideoClippingProperties;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
+
+import java.io.IOException;
+import java.nio.file.Path;
+import java.util.List;
+import java.util.concurrent.atomic.AtomicReference;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+class ContactSheetGeneratorTest {
+
+    @TempDir
+    Path tempDir;
+
+    @Test
+    void generatesContactSheetWithConfiguredTileColumns() {
+        AtomicReference<List<String>> command = new AtomicReference<>();
+        VideoClippingProperties properties = new VideoClippingProperties();
+        properties.getEditing().setContactSheetColumns(4);
+        ContactSheetGenerator generator = new ContactSheetGenerator(properties, arguments -> {
+            command.set(arguments);
+            return new ContactSheetGenerator.ProcessResult(0, "ok");
+        });
+
+        String contactSheet = generator.generate(clip(), tempDir.resolve("contact-sheets"));
+
+        assertThat(contactSheet).isEqualTo(tempDir.resolve("contact-sheets/clip_00001.jpg").toString());
+        assertCommandPair(command.get(), "-i", "./clips/clip_00001.mp4");
+        assertCommandPair(command.get(), "-vf", "fps=1/2,scale=320:-1,tile=4x4");
+        assertCommandPair(command.get(), "-frames:v", "1");
+        assertThat(command.get().getLast()).endsWith("clip_00001.jpg");
+    }
+
+    @Test
+    void rejectsFfmpegFailures() {
+        ContactSheetGenerator generator = new ContactSheetGenerator(new VideoClippingProperties(), command ->
+                new ContactSheetGenerator.ProcessResult(1, "failed"));
+
+        assertThrows(IllegalStateException.class, () -> generator.generate(clip(), tempDir.resolve("contact-sheets")));
+    }
+
+    @Test
+    void reportsProcessStartupAndInterruptionFailures() {
+        assertThrows(IllegalStateException.class, () -> new ContactSheetGenerator(new VideoClippingProperties(), command -> {
+            throw new IOException("missing executable");
+        }).generate(clip(), tempDir.resolve("io")));
+
+        try {
+            assertThrows(IllegalStateException.class, () -> new ContactSheetGenerator(new VideoClippingProperties(), command -> {
+                throw new InterruptedException("stopped");
+            }).generate(clip(), tempDir.resolve("interrupted")));
+            assertTrue(Thread.currentThread().isInterrupted());
+        } finally {
+            Thread.interrupted();
+        }
+    }
+
+    private ClipAnalysis clip() {
+        return new ClipAnalysis(
+                "clip_00001",
+                "./clips/clip_00001.mp4",
+                8.0,
+                "h264",
+                "aac",
+                1920,
+                1080,
+                30.0,
+                List.of(),
+                null,
+                null,
+                0,
+                0,
+                0
+        );
+    }
+
+    private void assertCommandPair(List<String> command, String option, String value) {
+        int index = command.indexOf(option);
+        assertThat(index).isGreaterThanOrEqualTo(0);
+        assertThat(command.get(index + 1)).isEqualTo(value);
+    }
+}