Answers.Body: <p>The <code>-b:v</code> doesn't have effect here since <code>crf</code> was set. Drop crf for similar sizes. CRF varies the bitrate to do justice to the complexity of the video. It aims for keeping quality constant.</p>
  
  <p>Whether it's bitrate or CRF mode, the <code>maxrate</code> and <code>bufsize</code> do take effect.</p>
  
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2017-04-01T10:56:38.973Z
Answers.LastActivityDate: 2017-04-01T10:56:38.973Z
Answers.UserDisplayName: Gyan
Body: <p>I'm new to this compression thing. I use following command with the latest ffmpeg version to compress and downscale my 1080p videos.</p>
  
  <pre><code>ffmpeg -i input.mkv -af "aresample=async=1:first_pts=0" -c:v libx264 -crf 18 -preset medium -b:v 3000k -maxrate 3000k -bufsize 10000k -acodec aac -c:s copy -map 0 -vf scale=1280:-2 output.mkv
  </code></pre>
  
  <p>what i don't understand, two videos having same duration, only one audio stream. after compression one has filesize 2GB while other 5GB. Why so much difference?</p>
  
Comments.ContentLicense: CC BY-SA 3.0
Comments.CreationDate: 2017-03-31T17:20:34.843Z
Comments.Text: The `-b:v` doesn't have effect here since crf was set. Drop `crf` for similar sizes. CRF varies the bitrate to do justice to the complexity of the video. It aims for keeping quality constant.
Comments.UserDisplayName: Gyan
Tags: <ffmpeg>
Title: ffmpeg - two videos having same video length but different file size
UserDisplayName: Ergec
ThreadText: # ffmpeg - two videos having same video length but different file size
  
  (Asked by: username_0 on 2017-03-31)
  
  I'm new to this compression thing. I use following command with the latest ffmpeg version to compress and downscale my 1080p videos.
  
  ```
  ffmpeg -i input.mkv -af "aresample=async=1:first_pts=0" -c:v libx264 -crf 18 -preset medium -b:v 3000k -maxrate 3000k -bufsize 10000k -acodec aac -c:s copy -map 0 -vf scale=1280:-2 output.mkv
  
  ```
  
  what i don't understand, two videos having same duration, only one audio stream. after compression one has filesize 2GB while other 5GB. Why so much difference?
  
  **Tags:** ffmpeg
  
  > **Comments:**
  > **username_1**: The `-b:v` doesn't have effect here since crf was set. Drop `crf` for similar sizes. CRF varies the bitrate to do justice to the complexity of the video. It aims for keeping quality constant.  
  
  ---
  
  ## 1 answers
  
  ### Answer by username_1 on 2017-04-01. Score: 4 | Accepted answer
  
  The `-b:v` doesn't have effect here since `crf` was set. Drop crf for similar sizes. CRF varies the bitrate to do justice to the complexity of the video. It aims for keeping quality constant.
  
  Whether it's bitrate or CRF mode, the `maxrate` and `bufsize` do take effect.
  
  
  ---
  
  