feat: send SIGINT to ffmpeg process on ctrl+c

Also show user a message to indicate they cancelled the encoding and that they should clean up the created file(s).
fix: print ffmpeg command for every video file when dry-running if a directory was passed in

cmds.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"log"
 	"os"
+	"os/exec"
 	"path/filepath"
 	"sort"
 	"strings"
@@ -20,6 +21,10 @@ type updateEstimate struct {
 	estimate int
 }
 
+type ffmpegProcessStart struct {
+	cmd *exec.Cmd
+}
+
 type initUi struct {
 	fileCount int
 	files     []string