添加视频帧提取功能和阿里云OSS存储支持

- 新增从视频素材提取首帧/尾帧的功能，支持画面连续性编辑
- 添加阿里云OSS存储支持，可配置本地或OSS存储方式
- 导入视频素材时自动探测并更新视频时长信息
- 前端添加从素材提取尾帧的UI界面
- 添加FramePrompt模型的数据库迁移

Co-Authored-By: Claude <noreply@anthropic.com>

infrastructure/external/ffmpeg/ffmpeg.go

@@ -853,3 +853,72 @@ func (f *FFmpeg) generateSilence(outputPath string, duration float64) (string, e
 	f.log.Infow("Silence audio generated successfully", "output", outputPath)
 	return outputPath, nil
 }
+
+// ExtractFrame 从视频中提取指定位置的帧
+// position: "first" 提取首帧, "last" 提取尾帧
+// 返回提取的图片文件路径
+func (f *FFmpeg) ExtractFrame(videoURL, outputPath, position string) (string, error) {
+	f.log.Infow("Extracting frame from video", "url", videoURL, "position", position, "output", outputPath)
+
+	// 下载视频文件
+	downloadPath := filepath.Join(f.tempDir, fmt.Sprintf("video_%d.mp4", time.Now().Unix()))
+	localVideoPath, err := f.downloadVideo(videoURL, downloadPath)
+	if err != nil {
+		return "", fmt.Errorf("failed to download video: %w", err)
+	}
+	defer os.Remove(localVideoPath)
+
+	// 确保输出目录存在
+	outputDir := filepath.Dir(outputPath)
+	if err := os.MkdirAll(outputDir, 0755); err != nil {
+		return "", fmt.Errorf("failed to create output directory: %w", err)
+	}
+
+	var cmd *exec.Cmd
+
+	if position == "last" {
+		// 提取尾帧：先获取视频时长，然后提取最后一帧
+		duration, err := f.GetVideoDuration(localVideoPath)
+		if err != nil {
+			return "", fmt.Errorf("failed to get video duration: %w", err)
+		}
+
+		// 提取最后一帧（时长减去0.1秒的位置）
+		seekTime := duration - 0.1
+		if seekTime < 0 {
+			seekTime = 0
+		}
+
+		cmd = exec.Command("ffmpeg",
+			"-ss", fmt.Sprintf("%.2f", seekTime),
+			"-i", localVideoPath,
+			"-vframes", "1",
+			"-q:v", "2",
+			"-y",
+			outputPath,
+		)
+	} else {
+		// 默认提取首帧
+		cmd = exec.Command("ffmpeg",
+			"-i", localVideoPath,
+			"-vframes", "1",
+			"-q:v", "2",
+			"-y",
+			outputPath,
+		)
+	}
+
+	output, err := cmd.CombinedOutput()
+	if err != nil {
+		f.log.Errorw("FFmpeg frame extraction failed", "error", err, "output", string(output))
+		return "", fmt.Errorf("ffmpeg frame extraction failed: %w, output: %s", err, string(output))
+	}
+
+	// 检查输出文件是否存在
+	if _, err := os.Stat(outputPath); os.IsNotExist(err) {
+		return "", fmt.Errorf("frame extraction failed: output file not created")
+	}
+
+	f.log.Infow("Frame extracted successfully", "output", outputPath, "position", position)
+	return outputPath, nil
+}