We know the FFMPEG is very helpful on Multimedia oriented task, like video/Audio conversion, change the formats, make different formats and etc. Also burn subtitles into your video using the libass library. 

To enable libass library  you need to configure FFmpeg with --enable-libass.

also build with libavcodec and libavformat to convert the add subtitles file to ASS (Advanced Substation Alpha) subtitles format.

Install and configure with FFmpeg,

# yum install libass libass-devel

# cd ffmpeg

# ./configure --enable-shared --enable-nonfree --enable-gpl --enable-pthreads --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libfaac --enable-libmp3lame --enable-libass

# make

# make install

Do you need to create a subtitle set the format on .srt file (subtitle.srt)
00:00:02,000 --> 00:00:04,600
Hey, how are you ?

00:00:6,900 --> 00:00:7,700
yeah fine, thank you ?​ 

# ffmpeg -i your_video_format.mp4 -vf subtitles=subtitle.srt -c:a copy with_subtitle_video.mp4