user16682: I use ffmpeg to convert a 3gp video to MP4. You can see a part of output of ffmpeg here:
ffmpeg version N-79139-gde1a0d4 Copyright (c) 2000-2016 the FFmpeg developers

...
Input #0, 

...
    Metadata:
      rotate          : 90
      creation_time   : ...
      handler_name    : VideoHandle
      encoder         :                                
    Side data:
      displaymatrix: rotation of -90.00 degrees
    ...

I use noautorotate option in below command to avoid auto rotate based on metadata of file and it is successful:

ffmpeg -noautorotate -i $vid -qscale 0 -acodec libmp3lame -ar 44100 -ab 128k ../MP4/$(basename $vid).mp4

Then I tried this HTML code to open converted file in a browser(for example by Google Chrome):
<!DOCTYPE html>
<html>
<body>

<video width="320" height="240" controls>
  <source src="../videos/test.mp4" type="video/mp4">
</video>

</body>
</html>

But when I open that, video shown rotated. How I can solve this problem? Is there a tag or any other thing to disable autorotate in HTML?

user1871: Although noautorotate stops FFmpeg from rotating the video, it does not remove the rotation tag from the output. So, you have to set the tag manually.
ffmpeg -noautorotate -i $vid .....  -metadata:s:v rotate=0 output.mp4 


16682: <p>I use <code>ffmpeg</code> to convert a <code>3gp</code> video to <code>MP4</code>. You can see a part of output of <code>ffmpeg</code> here:</p>

<pre><code>ffmpeg version N-79139-gde1a0d4 Copyright (c) 2000-2016 the FFmpeg developers
</code></pre>

<p>...</p>

<pre><code>Input #0, 

...
    Metadata:
      rotate          : 90
      creation_time   : ...
      handler_name    : VideoHandle
      encoder         :                                
    Side data:
      displaymatrix: rotation of -90.00 degrees
    ...
</code></pre>

<p>I use <code>noautorotate</code> option in below command to avoid auto rotate based on metadata of file and it is successful:</p>

<blockquote>
  <p>ffmpeg -noautorotate -i $vid -qscale 0 -acodec libmp3lame -ar 44100 -ab 128k ../MP4/$(basename $vid).mp4</p>
</blockquote>

<p>Then I tried this HTML code to open converted file in a browser(for example by <code>Google Chrome</code>):</p>

<pre><code>&lt;!DOCTYPE html&gt;
&lt;html&gt;
&lt;body&gt;

&lt;video width="320" height="240" controls&gt;
  &lt;source src="../videos/test.mp4" type="video/mp4"&gt;
&lt;/video&gt;

&lt;/body&gt;
&lt;/html&gt;
</code></pre>

<p>But when I open that, video shown rotated. How I can solve this problem? Is there a tag or any other thing to disable autorotate in HTML?</p>
 1871: <p>Although <code>noautorotate</code> stops FFmpeg from rotating the video, it does not remove the rotation tag from the output. So, you have to set the tag manually.</p>

<pre><code>ffmpeg -noautorotate -i $vid .....  -metadata:s:v rotate=0 output.mp4 
</code></pre>
