HLD: Design YouTube - Video Streaming Platform

public class VideoUploadService {
    public UploadResponse uploadVideo(MultipartFile file, VideoMetadata metadata, String userId) {
        String videoId = generateId();
        
        String rawPath = s3Client.upload(file, "raw-videos/" + videoId);
        
        Video video = new Video(videoId, userId, metadata, VideoStatus.PROCESSING);
        videoRepository.save(video);
        
        kafkaTemplate.send("video-processing", new VideoUploadedEvent(videoId, rawPath));
        
        return new UploadResponse(videoId, "Processing started");
    }
}
public class VideoProcessingService {
    private static final int[] RESOLUTIONS = {360, 480, 720, 1080, 1440, 2160};
    
    public void processVideo(String videoId, String rawPath) {
        File rawFile = downloadFromS3(rawPath);
        
        for (int resolution : RESOLUTIONS) {
            String outputPath = transcodeToResolution(rawFile, resolution);
            s3Client.upload(outputPath, "processed/" + videoId + "/" + resolution + ".mp4");
        }
        
        String thumbnailPath = generateThumbnail(rawFile);
        s3Client.upload(thumbnailPath, "thumbnails/" + videoId + ".jpg");
        
        videoRepository.updateStatus(videoId, VideoStatus.READY);
    }
}

public class StreamingService {
    public StreamingUrl getStreamUrl(String videoId, String userId, int quality) {
        Video video = videoRepository.findById(videoId);
        
        int bestQuality = selectQuality(quality, getUserBandwidth(userId));
        
        String cdnUrl = cdnService.getSignedUrl(
            "processed/" + videoId + "/" + bestQuality + ".mp4",
            Duration.ofHours(4)
        );
        
        analyticsService.trackView(videoId, userId);
        
        return new StreamingUrl(cdnUrl, bestQuality);
    }
}

public class RecommendationService {
    public List<Video> getRecommendations(String userId, int limit) {
        List<Video> recommendations = new ArrayList<>();
        
        List<String> watchHistory = userService.getWatchHistory(userId, 100);
        Map<String, Double> categoryScores = calculateCategoryPreferences(watchHistory);
        
        List<Video> trending = getTrendingVideos(limit / 3);
        recommendations.addAll(trending);
        
        List<Video> collaborative = collaborativeFilter(userId, limit / 3);
        recommendations.addAll(collaborative);
        
        List<Video> contentBased = contentBasedFilter(categoryScores, limit / 3);
        recommendations.addAll(contentBased);
        
        return rankAndDeduplicate(recommendations, limit);
    }
}

CREATE TABLE videos (
    video_id VARCHAR(50) PRIMARY KEY,
    user_id VARCHAR(50),
    title VARCHAR(200),
    description TEXT,
    duration_seconds INT,
    status VARCHAR(20),
    view_count BIGINT DEFAULT 0,
    like_count BIGINT DEFAULT 0,
    created_at TIMESTAMP
);
CREATE TABLE video_views (
    view_id BIGINT PRIMARY KEY,
    video_id VARCHAR(50),
    user_id VARCHAR(50),
    watched_duration INT,
    quality INT,
    viewed_at TIMESTAMP
);