✨ feat: rewrite in Go

src/frameformat.go

@@ -0,0 +1,91 @@
+package main
+
+import (
+	"bufio"
+	"encoding/binary"
+	"fmt"
+	"math"
+	"os"
+)
+
+// .tsf container, little-endian: "TSFR" | version uint16 | fps float64 |
+// count uint32 | count × (length uint32, JPEG bytes).
+const (
+	tsfMagic   = "TSFR"
+	tsfVersion = 1
+)
+
+func writeTSF(output string, data *FramesContainer) error {
+	f, err := os.Create(output)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	w := bufio.NewWriterSize(f, 1<<20)
+	if _, err := w.WriteString(tsfMagic); err != nil {
+		return err
+	}
+	var hdr [14]byte
+	binary.LittleEndian.PutUint16(hdr[0:], tsfVersion)
+	binary.LittleEndian.PutUint64(hdr[2:], math.Float64bits(data.FPS))
+	binary.LittleEndian.PutUint32(hdr[10:], uint32(len(data.Frames)))
+	if _, err := w.Write(hdr[:]); err != nil {
+		return err
+	}
+
+	var lenBuf [4]byte
+	for _, frame := range data.Frames {
+		binary.LittleEndian.PutUint32(lenBuf[:], uint32(len(frame)))
+		if _, err := w.Write(lenBuf[:]); err != nil {
+			return err
+		}
+		if _, err := w.Write(frame); err != nil {
+			return err
+		}
+	}
+	return w.Flush()
+}
+
+func loadTSF(filename string) (*FramesContainer, error) {
+	raw, err := os.ReadFile(filename)
+	if err != nil {
+		return nil, err
+	}
+	invalid := func() error {
+		return fmt.Errorf("invalid frames file %q: corrupt .tsf container", filename)
+	}
+
+	if len(raw) < 18 || string(raw[:4]) != tsfMagic {
+		return nil, invalid()
+	}
+	version := binary.LittleEndian.Uint16(raw[4:])
+	if version != tsfVersion {
+		return nil, fmt.Errorf("unsupported .tsf version %d in %q", version, filename)
+	}
+	fps := math.Float64frombits(binary.LittleEndian.Uint64(raw[6:]))
+	count := binary.LittleEndian.Uint32(raw[14:])
+
+	frames := make([][]byte, 0, count)
+	off := 18
+	for range count {
+		if off+4 > len(raw) {
+			return nil, invalid()
+		}
+		n := int(binary.LittleEndian.Uint32(raw[off:]))
+		off += 4
+		if off+n > len(raw) {
+			return nil, invalid()
+		}
+		frames = append(frames, raw[off:off+n])
+		off += n
+	}
+
+	if len(frames) == 0 || fps <= 0 {
+		return nil, fmt.Errorf(
+			"invalid frames file %q: expected non-empty frames and a positive fps",
+			filename,
+		)
+	}
+	return &FramesContainer{Frames: frames, FPS: fps}, nil
+}