I am trying to add text to video using ffmpeg and wants text to appear for a given period of time. I am trying to use DrawText filter but don\'t know how to provide time per
The drawtext video filter has timeline editing support (see the output of ffmpeg -filters). This can evaluate an expression and allows you to provide the time(s) of when the filter should be enabled.
This example will enable the filter from 12 seconds to 3 minutes:
ffmpeg -i input.mp4 -vf "drawtext=enable='between(t,12,3*60)':fontfile=/usr/share/fonts/truetype/freefont/FreeSerif.ttf: text='Test Text'" -acodec copy output.mp4
The audio was stream copied in this example.
If you do not have timeline editing support then you will need to get a newer version. You can simply download a Linux build of ffmpeg or follow a step-by-step guide to compile ffmpeg.
Also see the FFmpeg and x264 Encoding Guide.