feat: sync GIFv and saved GIF support

internal/app/files/gif_transcoder_test.go

@@ -0,0 +1,39 @@
+package files
+
+import (
+	"bytes"
+	"context"
+	"image"
+	"image/color"
+	"image/gif"
+	"testing"
+)
+
+func TestFFmpegGIFTranscoderProducesCanonicalMP4(t *testing.T) {
+	transcoder, err := NewFFmpegGIFTranscoder()
+	if err != nil {
+		t.Skipf("ffmpeg/ffprobe unavailable: %v", err)
+	}
+	palette := color.Palette{color.Black, color.White}
+	first := image.NewPaletted(image.Rect(0, 0, 3, 5), palette)
+	second := image.NewPaletted(image.Rect(0, 0, 3, 5), palette)
+	for i := range second.Pix {
+		second.Pix[i] = 1
+	}
+	var input bytes.Buffer
+	if err := gif.EncodeAll(&input, &gif.GIF{
+		Image: []*image.Paletted{first, second}, Delay: []int{10, 10}, LoopCount: 0,
+	}); err != nil {
+		t.Fatal(err)
+	}
+	result, err := transcoder.Transcode(context.Background(), input.Bytes())
+	if err != nil {
+		t.Fatalf("Transcode: %v", err)
+	}
+	if len(result.Data) < 12 || string(result.Data[4:8]) != "ftyp" {
+		t.Fatalf("output is not MP4: %x", result.Data[:min(len(result.Data), 16)])
+	}
+	if result.Width != 4 || result.Height != 6 || result.Duration <= 0 {
+		t.Fatalf("metadata = %+v, want even 4x6 positive duration", result)
+	}
+}