feat: add /render/mp4 endpoint with FFmpeg encoding

- Add MP4Request type with fps param
- Render frames in parallel, encode via ffmpeg
- Add ffmpeg to Docker image

internal/render/mp4.go

@@ -0,0 +1,102 @@
+package render
+
+import (
+	"fmt"
+	"image/png"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"sync"
+
+	"github.com/hytale-tools/blockymodel-merger/pkg/texture"
+)
+
+// RenderMP4 renders a GLB model to an MP4 video rotating 360 degrees
+func RenderMP4(glbBytes []byte, atlas *texture.Atlas, background string, frames, width, height, fps int) ([]byte, error) {
+	// Parse background color
+	bgColor, err := ParseHexColor(background)
+	if err != nil {
+		return nil, fmt.Errorf("invalid background color: %w", err)
+	}
+
+	// Get atlas image
+	var atlasImage = atlas.Image
+
+	// Convert GLB to mesh
+	mesh, err := GLBToMesh(glbBytes, atlasImage)
+	if err != nil {
+		return nil, fmt.Errorf("converting GLB to mesh: %w", err)
+	}
+
+	// Create temp directory for frames
+	tempDir, err := os.MkdirTemp("", "blockyserver-mp4-*")
+	if err != nil {
+		return nil, fmt.Errorf("creating temp directory: %w", err)
+	}
+	defer os.RemoveAll(tempDir)
+
+	// Calculate rotation per frame
+	rotationPerFrame := 360.0 / float64(frames)
+
+	// Render all frames in parallel
+	var wg sync.WaitGroup
+	errChan := make(chan error, frames)
+
+	for i := 0; i < frames; i++ {
+		wg.Add(1)
+		go func(frameIdx int) {
+			defer wg.Done()
+			rotation := float64(frameIdx) * rotationPerFrame
+			img := RenderScene(mesh, atlasImage, rotation, width, height, bgColor)
+
+			// Write frame to temp file
+			framePath := filepath.Join(tempDir, fmt.Sprintf("frame_%04d.png", frameIdx))
+			f, err := os.Create(framePath)
+			if err != nil {
+				errChan <- fmt.Errorf("creating frame file: %w", err)
+				return
+			}
+			defer f.Close()
+
+			if err := png.Encode(f, img); err != nil {
+				errChan <- fmt.Errorf("encoding frame PNG: %w", err)
+				return
+			}
+		}(i)
+	}
+	wg.Wait()
+	close(errChan)
+
+	// Check for errors
+	for err := range errChan {
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	// Run FFmpeg to encode MP4
+	outputPath := filepath.Join(tempDir, "output.mp4")
+	inputPattern := filepath.Join(tempDir, "frame_%04d.png")
+
+	cmd := exec.Command("ffmpeg",
+		"-y",
+		"-framerate", fmt.Sprintf("%d", fps),
+		"-i", inputPattern,
+		"-c:v", "libx264",
+		"-pix_fmt", "yuv420p",
+		"-movflags", "+faststart",
+		outputPath,
+	)
+
+	if output, err := cmd.CombinedOutput(); err != nil {
+		return nil, fmt.Errorf("ffmpeg encoding failed: %w\nOutput: %s", err, string(output))
+	}
+
+	// Read output file
+	mp4Bytes, err := os.ReadFile(outputPath)
+	if err != nil {
+		return nil, fmt.Errorf("reading output MP4: %w", err)
+	}
+
+	return mp4Bytes, nil
+}