<p>The scale filter has no effect on the encoder's bitrate control. </p>

<p>Yes, a scaled down video should have a lower bitrate <strong>if</strong> it is encoded with the same encoder settings as the source. In your command, since no encoder parameters are explicitly set, ffmpeg defaults to encoder <code>x264</code> with rate-control mode CRF with value 23. Apparently, this results in the same bitrate as the full-sized source. Set a higher value to reduce size.</p>

<pre><code>ffmpeg -i input.mp4 -vf scale=2160:2160 -crf 26 output.mp4
</code></pre>

CC BY-SA 3.0
2017-06-06T05:53:22.787Z
This makes no sense. Why would you have to change crf? That's "constant quality", right? This means that we should expect a lower bitrate on a down scale.
user3643
CC BY-SA 3.0
2017-06-06T05:56:49.377Z
@DigiVisionMedia crf is "constant ratefactor". also, this all is searchable in the web, don't be lazy please.
Display Name
CC BY-SA 3.0
2017-06-06T05:58:27.150Z
Wouldn't this make a lesser quality encode?
user3643
CC BY-SA 3.0
2017-06-10T12:27:51.420Z
hmm, need 50 rep to comment... so posting instead. **increase** crf to **reduce** bit rate, also reduces quality<br>
**decrease** crf to **increase** bit rate, improves quality<br>
+/- 6 crf is about half / double the bitrate (at least for x265). good intro:<br>
http://slhck.info/video/2017/02/24/crf-guide.html
netjiro
CC BY-SA 3.0
2017-06-06T05:34:25.947Z
2017-06-06T05:34:25.947Z
Gyan
<p>I have a 3000 by 3000 VR video encoded in H264. I scaled down the video by</p>

<pre><code>ffmpeg -i input.mp4 -vf scale=2160:2160 output.mp4
</code></pre>

<p>To my surprise, the bit rate of <code>output.mp4</code> did not decrease (in fact, it increased a little bit).</p>

<p>Is not a scaled down video supposed to have lower bit rate than the original video? What is the mechanism of <code>-vf scale=***</code>?</p>

<ffmpeg><scale><libx264>
I scaled down a video, but the bit rate does not change
shintaroid
# I scaled down a video, but the bit rate does not change

(Asked by: username_0 on 2017-06-05)

I have a 3000 by 3000 VR video encoded in H264. I scaled down the video by
ffmpeg -i input.mp4 -vf scale=2160:2160 output.mp4

To my surprise, the bit rate of output.mp4 did not decrease (in fact, it increased a little bit).
Is not a scaled down video supposed to have lower bit rate than the original video? What is the mechanism of -vf scale=***?

**Tags:** ffmpeg, scale, libx264


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## 1 answers

### Answer by username_1 on 2017-06-06. Score: 1 | Accepted answer

The scale filter has no effect on the encoder's bitrate control. 
Yes, a scaled down video should have a lower bitrate if it is encoded with the same encoder settings as the source. In your command, since no encoder parameters are explicitly set, ffmpeg defaults to encoder x264 with rate-control mode CRF with value 23. Apparently, this results in the same bitrate as the full-sized source. Set a higher value to reduce size.
ffmpeg -i input.mp4 -vf scale=2160:2160 -crf 26 output.mp4

> **Comments:**
> **username_2**: This makes no sense. Why would you have to change crf? That's "constant quality", right? This means that we should expect a lower bitrate on a down scale.  
> **username_3**: @DigiVisionMedia crf is "constant ratefactor". also, this all is searchable in the web, don't be lazy please.  
> **username_2**: Wouldn't this make a lesser quality encode?  
> **username_4**: hmm, need 50 rep to comment... so posting instead. **increase** crf to **reduce** bit rate, also reduces quality<br> **decrease** crf to **increase** bit rate, improves quality<br> +/- 6 crf is about half / double the bitrate (at least for x265). good intro:<br> http://slhck.info/video/2017/02/24/crf-guide.html  

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