The aspect ratio of the RED camera is 17:9 (1.90:1). Since we edit in a 16:9 (1.78:1) workspace, Media Composer will squish the image to meet that ratio. Taking the following steps will correct for this.
Go to your synced clips bin and select all the clips.
Right-click and select “Source Settings…” in the drop down menu.
In the FrameFlex tab, set Reformat to “Letterbox / Pillarbox”. Click “Apply to all” and then “OK”.
Your footage should now be presented in the correct aspect ratio. The black bars at the top and bottom are normal and intended for the RED Camera’s aspect ratio. (You may need to refresh your sequence if the change does not show immediately.)
After this process is done, if you wish to change the aspect ratio to one of the other approved aspect ratios, you can apply one of the masks from the frame.io folder.