title: FFmpeg does not convert .ts files to .mp4
body: <p>I am trying to run this code to convert a .ts file in my Google Colab to a .mp4 file:</p>
  <pre><code>import subprocess
  
  infile = '/content/result/00000.ts'
  outfile = '/content/result/video.mp4'
  
  subprocess.run(['ffmpeg', '-i', infile, outfile])
  </code></pre>
  <p>However, I don't see anything in <code>/content/result/</code> except the .ts files.  This is the output cell:</p>
  <pre><code>CompletedProcess(args=['ffmpeg', '-i', '/content/result/00000.ts', '/content/result/video.mp4'], returncode=1)
  </code></pre>