ok, I manage to remove threads and yes, QProcess is async, but..seems that tries to convert all at the same time, that's why I was using waitforfinish...my updated codes:
Qt Code: 
  1. #ifndef TEST01_HPP
  2. #define TEST01_HPP
  3.  
  4. #include <QApplication>
  5. #include <QWidget>
  6. #include <QFileDialog>
  7. #include <QDir>
  8. #include <QDesktopServices> // Qt 4.2
  9. #include "ui_test01.h"
  10. #include "ffmpeg_runner.hpp"
  11.  
  12. namespace Ui {
  13. 	class Form;
  14. };
  15.  
  16. class MyForm : public QWidget {
  17. 	Q_OBJECT
  18. 	private:
  19. 		Ui::Form *ui;
  20. 		MyFfmpegRunnerClass *ffmpeg;
  21. 	public:
  22. 		MyForm(QWidget *root = 0) : QWidget(root), ui(new Ui::Form)
  23. 		{
  24. 			ui->setupUi(this);
  25.  
  26. 			/* below is beta, watch it!!! */
  27. 			ffmpeg = new MyFfmpegRunnerClass(this);
  28. 			connect(ffmpeg, SIGNAL(startJob()), this, SLOT(handleStart()));
  29. 			connect(ffmpeg, SIGNAL(endJob()), this, SLOT(handleEnd()));
  30. 			/* ... */
  31.  
  32. 			connect(ui->pushButton, SIGNAL(clicked()), this, SLOT(handleRunButton()));
  33. 			connect(ui->pushButton_3, SIGNAL(clicked()), this, SLOT(handleBrowseButton())); 
  34. 			ui->lineEdit->setText(QDesktopServices::storageLocation(QDesktopServices::MoviesLocation));
  35. 		}
  36. 		virtual ~MyForm() {
  37. 			delete ffmpeg;
  38. 			delete ui;
  39. 		}
  40.  
  41. 	protected:
  42.  
  43. 	signals:
  44. 		void doneJob();
  45.  
  46. 	protected slots:
  47. 		void handleBrowseButton() {
  48. 			QString folder = QFileDialog::getExistingDirectory(this);
  49. 			if (!folder.isEmpty()) ui->lineEdit->setText(folder);
  50. 		}
  51.  
  52. 		void handleRunButton() {
  53. 			QString source_dir = ui->lineEdit->text();
  54. 			QString target_dir = QDesktopServices::storageLocation(QDesktopServices::MusicLocation);
  55. 			bool delete_me = true;
  56. 			ffmpeg->Start(source_dir, target_dir, delete_me);
  57. 		}
  58.  
  59. 		void handleStart() {
  60. 			qDebug() << "We start the process";
  61. 		}
  62.  
  63. 		void handleEnd() {
  64. 			qDebug() << "Done :v";
  65. 		}
  66.  
  67. };
  68.  
  69. #endif
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Qt Code: 
  1. #ifndef FFMPEG_RUNNER_HPP
  2. #define FFMPEG_RUNNER_HPP
  3.  
  4. #include <QDebug>
  5. #include <QDir>
  6. #include <QFileInfo>
  7. #include <QProcess>
  8.  
  9. class MyFfmpegRunnerClass : public QObject {
  10. 	Q_OBJECT
  11. 	private:
  12. 		QProcess *process;
  13. 		QString curr_file;
  14. 		bool delete_me;
  15. 		int n_files;
  16. 	public:
  17. 		MyFfmpegRunnerClass(QObject *parent = 0) : QObject(parent)
  18. 		{
  19. 			n_files = 0;
  20. 			process = new QProcess(this);			
  21. 			process->setStandardOutputFile("/dev/null");
  22. 			process->setStandardErrorFile("/dev/null");
  23. 			connect(process, SIGNAL(started()), this, SLOT(handleprocessStarted()));
  24. 			connect(process, SIGNAL(finished(int, QProcess::ExitStatus)), this, SLOT(handleprocessExited(int, QProcess::ExitStatus)));
  25. 		}
  26.  
  27. 		void Start(const QString& srcdir, const QString& outdir, bool be_deleted = false) {
  28. 			QDir folder(srcdir);
  29. 			folder.setNameFilters(QStringList() << "*.mp3" << "*.mp4" << "*.flv" << "*.wav" << "*.ogg" << "*.3gp");
  30. 			QStringList files = folder.entryList(QDir::NoDotAndDotDot|QDir::Files);
  31. 			delete_me = be_deleted;
  32. 			n_files = files.size();
  33. 			int index;
  34. 			for (index = 0; index != n_files; index++) {
  35. 					QFileInfo fi(srcdir, files.at(index));
  36. 					QString file = fi.baseName() + ".mp3";
  37. 					curr_file = fi.absoluteFilePath();
  38. 					QString out_file = QDir(outdir).filePath(file);
  39. 					qDebug() << "Converting: " << curr_file;
  40. 					process->start("ffmpeg", QStringList() << "-i" << curr_file << "-f" <<  "mp3" << "-ab" << "128k" << out_file);
  41. 			}
  42. 			// here we should wait until all files are converted, right?
  43.                        qDebug() << "Why do you see this line even the process is still converting?"
  44. 		}
  45.  
  46. 		~MyFfmpegRunnerClass() {
  47. 			if (process->pid()) process->close();
  48. 			delete process;
  49. 			qDebug() << "Class ffmpeg died";
  50. 		}
  51.  
  52. 	protected slots:
  53. 		void handleprocessStarted() {
  54. 			emit startJob();
  55. 		}
  56.  
  57. 		void handleprocessExited(int exitCode, QProcess::ExitStatus exitStatus) {
  58. 			qDebug() << "Exited code: " << exitCode << ". ExitStatus: " << exitStatus;
  59. 			if ( (exitCode == 0) && (delete_me) ) {
  60. 				process->close();
  61. 				emit endJob();
  62. 				// you should delete source file here
  63. 			}
  64. 		}
  65.  
  66. 	signals:
  67. 		void startJob();
  68. 		void endJob();
  69. };
  70.  
  71.  
  72. #endif
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