add conversion.go

conversion.go

@@ -0,0 +1,115 @@
+package main
+
+import (
+	"archive/zip"
+	"fmt"
+	"io"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+)
+
+// Create a file describing frames and their durations for FFmpeg's concat demuxer
+// https://ffmpeg.org/ffmpeg-formats.html#concat
+func makeConcatDemuxFile(manifest UgoiraManifest, frameDescFile *os.File) {
+	frames := manifest.Body.Frames
+	for _, frame := range frames {
+		frameDur := float32(frame.Delay) / 1000 // convert to seconds
+		frameDescFile.WriteString(fmt.Sprintf("file '%s'\n", frame.File))
+		frameDescFile.WriteString(fmt.Sprintf("duration %f\n", frameDur))
+	}
+	// repeat last frame (see: https://trac.ffmpeg.org/wiki/Slideshow#Concatdemuxer
+	lastFrame := frames[len(frames)-1]
+	frameDescFile.WriteString(fmt.Sprintf("file '%s'\n", lastFrame.File))
+}
+
+func callFFmpeg(frameDescPath, outputFilePath, workDir string) error {
+	// TODO: allow custom ffmpeg flags
+	const ffmpegArgs = `-hide_banner
+						-loglevel warning
+						-f concat -i %s
+						-an
+						-fps_mode vfr
+						-q:v 10
+						-c:v libvpx-vp9
+						-b:v 1M
+						-lossless 1 %s`
+
+	cmdArgs := fmt.Sprintf(ffmpegArgs, frameDescPath, outputFilePath)
+	cmdArgsSplit := strings.Fields(cmdArgs)
+	ffmpegProc := exec.Command("ffmpeg", cmdArgsSplit...)
+	ffmpegProc.Dir = workDir
+
+	if err := ffmpegProc.Run(); err != nil {
+		if exitErr, ok := err.(*exec.ExitError); ok {
+			return fmt.Errorf("ffmpeg exited with non zero code: %d", exitErr.ExitCode())
+		}
+		return fmt.Errorf("Could not run ffmpeg: %w", err)
+	}
+	return nil
+}
+
+// Reads and uncompress a frame from the archive and saves it
+func uncompressFrame(file *zip.File, framePath string) error {
+	fileFp, err := file.Open()
+	if err != nil {
+		return err
+	}
+	defer fileFp.Close()
+
+	outFp, err := os.Create(framePath)
+	if err != nil {
+		return err
+	}
+	defer outFp.Close()
+
+	if _, err := io.Copy(outFp, fileFp); err != nil {
+		return err
+	}
+	return nil
+}
+
+func unpackUgoira(ugoiraPath, outDir string) error {
+	reader, err := zip.OpenReader(ugoiraPath)
+	if err != nil {
+		return err
+	}
+	defer reader.Close()
+
+	for _, file := range reader.File {
+		path := filepath.Join(outDir, file.Name)
+		if err := uncompressFrame(file, path); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func ugoira2video(manifest UgoiraManifest, ugoiraFileName, vidOut string) error {
+	tdir, err := os.MkdirTemp("", "u2vwd-")
+	if err != nil {
+		return err
+	}
+	defer os.RemoveAll(tdir)
+
+	fraFp, err := os.CreateTemp(tdir, "frames*.txt")
+	if err != nil {
+		return err
+	}
+	defer os.Remove(fraFp.Name())
+	defer fraFp.Close()
+
+	vidOutAbs, err := filepath.Abs(vidOut)
+	if err != nil {
+		return err
+	}
+	if err := unpackUgoira(ugoiraFileName, tdir); err != nil {
+		return fmt.Errorf("Could not unpack Ugoira: %w", err)
+	}
+	makeConcatDemuxFile(manifest, fraFp)
+	if err := callFFmpeg(fraFp.Name(), vidOutAbs, tdir); err != nil {
+		return err
+	}
+	return nil
+}