user4297: I need a software which can blur a scene from a video file. I have thought about VirtualDub and Adobe Premiere but I am not sure if they provide the desired functionality.
My requirement is to blur a some-seconds scene for example blur the scene from 10:12 to 10:45 in a video file.

user2836: Premiere can certainly do what you need.  You could either cut the clip into sub-clips and apply a blur filter or you could apply a filter and keyframe the level of blur.  Note that this would be if you are trying to blur the entire frame.  If you want to blur only a portion of the frame, you would probably want something like motion tracking in After Effects that could follow the thing you want to blur and limit the blur to only the area impacted by a mask that follows the motion.

user4297: I fulfilled my requirement in Adobe Premiere Pro by following the below procedure:

Load the complete video in Timeline panel.
Using 'Razor' tool cut the section which I need to blur. When we cut using 'Razor' tool, Adobe Premiere Pro marks it as a logical separate clip.
Drag the Video → Blur effect on the desired clip and set the Gaussian blur settings.
Repeat the above steps for all other sections of the original video which I need to blur.
In the end, Export the complete sequence.


user1760: You can use ffmpeg, and you currently have a choice of four video filters that can blur: boxblur, sab, smartblur and unsharp. These filters can use the enable option for timeline support, so you can apply the blurring effect to a certain duration if desired. You can view what filters have timeline support with ffmpeg -filters.
Example


This example will apply the blur from 22-113 seconds, then again from 275-286 seconds:
ffmpeg -i input.avi -vf "boxblur=enable='between(t,22,113)',boxblur=enable='between(t,(60*4)+35,286)" -codec:a copy output.avi


You can enter seconds or have it calculate seconds for you as shown in the example.
Expression evaluation is not my best area. You may find a method to declare the filter just once.
Note that, since you only want to modify the video, the audio can be stream copied from the input to the output without re-encoding. This is faster than re-encoding and will preserve the quality. This is something most editors, such as Premiere, do not support without additional shenanigans.

Preview
If you have ffplay you can get a preview instead of encoding, watching, re-encoding...
ffplay -i input -vf smartblur

Getting ffmpeg
Builds are available for Windows, Linux, and OS X users. See the FFmpeg Download page, but of course you can always compile ffmpeg too.

4297: <p>I need a software which can blur a scene from a video file. I have thought about VirtualDub and Adobe Premiere but I am not sure if they provide the desired functionality.</p>

<p>My requirement is to blur a some-seconds scene for example blur the scene from 10:12 to 10:45 in a video file.</p>
 2836: <p>Premiere can certainly do what you need.  You could either cut the clip into sub-clips and apply a blur filter or you could apply a filter and keyframe the level of blur.  Note that this would be if you are trying to blur the entire frame.  If you want to blur only a portion of the frame, you would probably want something like motion tracking in After Effects that could follow the thing you want to blur and limit the blur to only the area impacted by a mask that follows the motion.</p>
 4297: <p>I fulfilled my requirement in Adobe Premiere Pro by following the below procedure:</p>

<ol>
<li><p>Load the complete video in Timeline panel.</p></li>
<li><p>Using 'Razor' tool cut the section which I need to blur. When we cut using 'Razor' tool, Adobe Premiere Pro marks it as a logical separate clip.</p></li>
<li><p>Drag the <em>Video → Blur</em> effect on the desired clip and set the Gaussian blur settings.</p></li>
<li><p>Repeat the above steps for all other sections of the original video which I need to blur.</p></li>
<li><p>In the end, Export the complete sequence.</p></li>
</ol>
 1760: <p>You can use ffmpeg, and you currently have a choice of four video filters that can blur: <a href="http://ffmpeg.org/ffmpeg-filters.html#boxblur" rel="noreferrer"><code>boxblur</code></a>, <a href="http://ffmpeg.org/ffmpeg-filters.html#sab" rel="noreferrer"><code>sab</code></a>, <a href="http://ffmpeg.org/ffmpeg-filters.html#smartblur-1" rel="noreferrer"><code>smartblur</code></a> and <a href="http://ffmpeg.org/ffmpeg-filters.html#unsharp" rel="noreferrer"><code>unsharp</code></a>. These filters can use the <code>enable</code> option for <a href="http://ffmpeg.org/ffmpeg-filters.html#Timeline-editing" rel="noreferrer">timeline</a> support, so you can apply the blurring effect to a certain duration if desired. You can view what filters have timeline support with <code>ffmpeg -filters</code>.</p>

<h3>Example</h3>

<p><img src="https://i.stack.imgur.com/iwCqE.png" alt="original image">
<img src="https://i.stack.imgur.com/ON6Hz.jpg" alt="boxblur"></p>

<p>This example will apply the blur from 22-113 seconds, then again from 275-286 seconds:</p>

<pre><code>ffmpeg -i input.avi -vf "boxblur=enable='between(t,22,113)',boxblur=enable='between(t,(60*4)+35,286)" -codec:a copy output.avi
</code></pre>

<ul>
<li><p>You can enter seconds or have it calculate seconds for you as shown in the example.</p></li>
<li><p><a href="http://ffmpeg.org/ffmpeg-utils.html#Expression-Evaluation" rel="noreferrer">Expression evaluation</a> is not my best area. You may find a method to declare the filter just once.</p></li>
<li><p>Note that, since you only want to modify the video, the audio can be <a href="https://ffmpeg.org/ffmpeg.html#Stream-copy" rel="noreferrer">stream copied</a> from the input to the output without re-encoding. This is faster than re-encoding and will preserve the quality. This is something most editors, such as Premiere, do not support without additional shenanigans.</p></li>
</ul>

<h3>Preview</h3>

<p>If you have <code>ffplay</code> you can get a preview instead of encoding, watching, re-encoding...</p>

<pre><code>ffplay -i input -vf smartblur
</code></pre>

<h3>Getting <code>ffmpeg</code></h3>

<p>Builds are available for Windows, Linux, and OS X users. See the <a href="https://ffmpeg.org/download.html" rel="noreferrer">FFmpeg Download</a> page, but of course you can always <a href="https://trac.ffmpeg.org/wiki/CompilationGuide" rel="noreferrer">compile <code>ffmpeg</code></a> too.</p>
