Captions can now be added to any Facebook video by uploading a srt with it.
Step 1 - Download Facebook SRT Format
Log into 3Play account and click on the file from the My Files page, click the Download button, click the Web Caption tab, and click the Facebook SRT format.
Step 2 - Add SRT File to Facebook Video
After you click Post, click Edit This Video.
Click Choose File to select the corresponding srt file from your computer. 
Click Save.
Additional languages can be added after after the video is saved.
To add captions in additional languages:
- Click your video to expand it.
- Click Edit This Video in the right column or click Options and select Edit This Video from the menu.
- Click Choose File to upload an additional SRT file from your computer. A backup language can be set that will caption the video if a viewer's preferred language isn't available.
- Click Save.
- Repeat steps 1-4 for each additional language you want to add.
Learn how to remove a caption file you've added to your video.
Note: To turn captions on or off, click the CC icon at the bottom of your video player.
Step 3- Adding Captions to an Existing Video on Facebook
If the video is already on Facebook and requires captions, click Photos. Find the video that requires captions and click on it. At the bottom click Options--> Edit This Video. Follow Step 3 to add captions.