convert a video to a gif, maybe

gif.go

package main

import (
	"fmt"
	"os"
	"os/exec"
	"path/filepath"
	"strings"
)

func main() {
	in, err := inPath()
	if err != nil {
		panic(err)
	}

	out, err := outPath(in)
	if err != nil {
		panic(err)
	}

	if err := convert(in, out); err != nil {
		panic(err)
	}
}

func inPath() (string, error) {
	if len(os.Args) < 2 {
		return "", fmt.Errorf("no input")
	}

	var in string

	in, err := filepath.Abs(os.Args[1])
	if err != nil {
		return "", err
	}

	if _, err := os.Stat(in); os.IsNotExist(err) {
		return "", fmt.Errorf("no such file: %s", in)
	}

	return in, nil
}

func outPath(in string) (string, error) {
	if len(os.Args) > 2 {
		out, err := filepath.Abs(os.Args[2])
		if err != nil {
			return "", err
		}

		return out, nil
	}

	out, err := filepath.Abs(strings.TrimSuffix(in, filepath.Ext(in)) + ".gif")
	if err != nil {
		return "", err
	}

	return out, nil
}

func convert(in, out string) error {
	if err := generatePalette(in); err != nil {
		return err
	}

	if err := convertToGif(in, out); err != nil {
		return err
	}

	return nil
}

func generatePalette(in string) error {
	args := []string{
		"-y",
		"-i",
		in,
		"-vf",
		"fps=15,scale=320:-1:flags=lanczos,palettegen",
		filepath.Join(os.TempDir(), "palette.gif"),
	}

	return run("ffmpeg", args...)
}

func convertToGif(in, out string) error {
	args := []string{
		"-y",
		"-i",
		in,
		"-i",
		filepath.Join(os.TempDir(), "palette.gif"),
		"-filter_complex",
		"fps=15,scale=400:-1:flags=lanczos[x];[x][1:v]paletteuse",
		out,
	}

	return run("ffmpeg", args...)
}

func run(command string, args ...string) error {
	cmd := exec.Command(command, args...)
	if output, err := cmd.CombinedOutput(); err != nil {
		fmt.Println(string(output))
		return err
	}

	return nil
}