Add GetTotalDuration method to FFprobeContract and implementation

Extend `FFprobeContract` interface with `GetTotalDuration` for retrieving the duration of media files.

internal/ffmpeg/ffprobe.go

@@ -5,11 +5,14 @@ import (
 	"fyne.io/fyne/v2/lang"
 	"git.kor-elf.net/kor-elf/gui-for-ffmpeg/internal/utils"
 	"os/exec"
+	"strconv"
 	"strings"
+	"unicode"
 )
 
 type FFprobeContract interface {
 	GetPath() string
+	GetTotalDuration(file *File) (float64, error)
 }
 
 type ffprobe struct {
@@ -38,6 +41,50 @@ func (f *ffprobe) GetPath() string {
 	return f.path
 }
 
+func (f *ffprobe) GetTotalDuration(file *File) (duration float64, err error) {
+	args := []string{"-v", "error", "-select_streams", "v:0", "-count_packets", "-show_entries", "stream=nb_read_packets", "-of", "csv=p=0", file.Path}
+	cmd := exec.Command(f.path, args...)
+	utils.PrepareBackgroundCommand(cmd)
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		errString := strings.TrimSpace(string(out))
+		if len(errString) > 1 {
+			return 0, errors.New(errString)
+		}
+		return 0, err
+	}
+	frames := strings.TrimSpace(string(out))
+	if len(frames) == 0 {
+		return f.getAlternativeTotalDuration(file)
+	}
+
+	duration, err = strconv.ParseFloat(frames, 64)
+	if err != nil {
+		// fix .mts duration
+		return strconv.ParseFloat(getFirstDigits(frames), 64)
+	}
+	return duration, err
+}
+
+func (f *ffprobe) getAlternativeTotalDuration(file *File) (duration float64, err error) {
+	args := []string{"-v", "error", "-select_streams", "a:0", "-count_packets", "-show_entries", "stream=nb_read_packets", "-of", "csv=p=0", file.Path}
+	cmd := exec.Command(f.path, args...)
+	utils.PrepareBackgroundCommand(cmd)
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		errString := strings.TrimSpace(string(out))
+		if len(errString) > 1 {
+			return 0, errors.New(errString)
+		}
+		return 0, err
+	}
+	frames := strings.TrimSpace(string(out))
+	if len(frames) == 0 {
+		return 0, errors.New("error getting number of frames")
+	}
+	return strconv.ParseFloat(frames, 64)
+}
+
 func checkFFprobePath(path string) (bool, error) {
 	cmd := exec.Command(path, "-version")
 	utils.PrepareBackgroundCommand(cmd)
@@ -50,3 +97,15 @@ func checkFFprobePath(path string) (bool, error) {
 	}
 	return true, nil
 }
+
+func getFirstDigits(s string) string {
+	result := ""
+	for _, r := range s {
+		if unicode.IsDigit(r) {
+			result += string(r)
+		} else {
+			break
+		}
+	}
+	return result
+}