I want it to do the ffmpeg convert while the application continues to run

Downloading with yd-dl.exe is successful, but it does not convert the downloaded video to mp4 with ffmpeg. When I stop compiling the project in visual studio, it converts the ffmpeg file to mp4.

using System;
using System.Diagnostics;
using System.IO;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace YouTube_MP4_indir
{
 public partial class Form1 : Form
 {
 public Form1()
 {
 InitializeComponent();
 pictureBox2.Visible = false;
 pictureBox3.Visible = false;
 }

 private async void btnDownload_Click(object sender, EventArgs e)
 {
 searchBox.Enabled = false;
 btnDownload.Enabled = false;
 pictureBox2.Visible = true;
 pictureBox3.Visible = false;

 string url = searchBox.Text.Trim();
 if (string.IsNullOrEmpty(url))
 {
 DialogResult result = MessageBox.Show("Lütfen geçerli bir YouTube URL'si giriniz.", "Uyarı", MessageBoxButtons.OK, MessageBoxIcon.Warning);

 if (result == DialogResult.OK)
 {
 searchBox.Text = "";
 searchBox.Enabled = true;
 btnDownload.Enabled = true;
 }

 pictureBox2.Visible = false;
 pictureBox3.Visible = false;
 return;
 }

 string desktopPath = Environment.GetFolderPath(Environment.SpecialFolder.Desktop);
 string videosFolderPath = Path.Combine(desktopPath, "Videolar");

 if (!Directory.Exists(videosFolderPath))
 {
 Directory.CreateDirectory(videosFolderPath);
 }

 string videoTitle = await GetVideoTitle(url);

 if (string.IsNullOrEmpty(videoTitle))
 {
 MessageBox.Show("Video başlığı alınamadı.", "Hata", MessageBoxButtons.OK, MessageBoxIcon.Error);
 pictureBox2.Visible = false;
 pictureBox3.Visible = false;
 return;
 }

 string inputFilePath = Path.Combine(videosFolderPath, $"{videoTitle}.mp4");
 string outputFilePath = Path.Combine(videosFolderPath, $"{videoTitle}-dönüştürülmüş.mp4");

 try
 {
 var ytDlpPath = Path.Combine(Application.StartupPath, "files", "yt-dlp.exe");

 var startInfo = new ProcessStartInfo()
 {
 FileName = ytDlpPath,
 Arguments = $"-f bestvideo[height<=1080]+bestaudio/best --merge-output-format mp4 --output \"{inputFilePath}\" {url}",
 UseShellExecute = false,
 CreateNoWindow = true,
 RedirectStandardOutput = true,
 RedirectStandardError = true
 };

 var process = Process.Start(startInfo);
 string output = await process.StandardOutput.ReadToEndAsync();
 string error = await process.StandardError.ReadToEndAsync();

 await process.WaitForExitAsync();

 if (process.ExitCode == 0)
 {
 // Paralel olarak FFmpeg dönüştürme işlemini başlat
 _ = Task.Run(() => ConvertToMp4(inputFilePath, outputFilePath));

 MessageBox.Show("İndirme tamamlandı. Video dönüştürülüyor.", "Bilgi", MessageBoxButtons.OK, MessageBoxIcon.Information);

 searchBox.Text = "";
 searchBox.Enabled = true;
 btnDownload.Enabled = true;

 pictureBox2.Visible = false;
 pictureBox3.Visible = true;
 }
 else
 {
 MessageBox.Show("Lütfen sadece video linki giriniz", "Uyarı", MessageBoxButtons.OK, MessageBoxIcon.Warning);

 pictureBox2.Visible = false;
 pictureBox3.Visible = false;
 }
 }
 catch (Exception ex)
 {
 MessageBox.Show("Hata: "+ ex.Message, "Hata", MessageBoxButtons.OK, MessageBoxIcon.Error);

 pictureBox2.Visible = false;
 pictureBox3.Visible = false;
 }
 }

 private async Task GetVideoTitle(string url)
 {
 try
 {
 var ytDlpPath = Path.Combine(Application.StartupPath, "files", "yt-dlp.exe");

 var startInfo = new ProcessStartInfo()
 {
 FileName = ytDlpPath,
 Arguments = $"-e {url}",
 UseShellExecute = false,
 CreateNoWindow = true,
 RedirectStandardOutput = true,
 RedirectStandardError = true
 };

 var process = Process.Start(startInfo);
 string output = await process.StandardOutput.ReadToEndAsync();
 await process.WaitForExitAsync();

 return output.Trim();
 }
 catch (Exception ex)
 {
 MessageBox.Show("Hata: "+ ex.Message, "Hata", MessageBoxButtons.OK, MessageBoxIcon.Error);
 return null;
 }
 }

 private async Task ConvertToMp4(string inputFilePath, string outputFilePath)
 {
 try
 {
 var ffmpegPath = Path.Combine(Application.StartupPath, "files", "ffmpeg.exe");

 var startInfo = new ProcessStartInfo
 {
 FileName = ffmpegPath,
 Arguments = $"-i \"{inputFilePath}\" -c:v libx264 -preset ultrafast -crf 23 -s hd1080 \"{outputFilePath}\"",
 UseShellExecute = false,
 CreateNoWindow = true,
 RedirectStandardOutput = true,
 RedirectStandardError = true
 };

 var process = Process.Start(startInfo);
 string output = await process.StandardOutput.ReadToEndAsync();
 string error = await process.StandardError.ReadToEndAsync();

 await process.WaitForExitAsync();

 if (process.ExitCode == 0)
 {
 MessageBox.Show("Dönüştürme işlemi başarılı.", "Bilgi", MessageBoxButtons.OK, MessageBoxIcon.Information);

 if (File.Exists(inputFilePath))
 {
 File.Delete(inputFilePath);
 }
 }
 else
 {
 MessageBox.Show("Dönüştürme sırasında bir hata oluştu: "+ error, "Hata", MessageBoxButtons.OK, MessageBoxIcon.Error);
 }
 }
 catch (Exception ex)
 {
 MessageBox.Show("Hata: "+ ex.Message, "Hata", MessageBoxButtons.OK, MessageBoxIcon.Error);
 }
 }

 private Form2 form2;

 private void button2_Click(object sender, EventArgs e)
 {
 if (form2 == null || form2.IsDisposed)
 {
 form2 = new Form2();
 form2.Show();
 }
 else
 {
 form2.BringToFront();
 }
 }
 }
}

Downloading with yd-dl.exe is successful. as soon as the video is downloaded I want to convert it to mp4 with ffmpeg but it won't convert without stopping the project.