useful ffmpeg commands

ffmpeg.rb

#1. Getting resolution of video using ffmpeg
# after running following command you will get output in format 640x480
`ffmpeg -i #{path_to_video} 2>&1 | grep 'Video:' | cut -d \, -f 3 | sed -e 's/\[PAR//g' -e 's/x/:/g' | cut -d ' ' -f 2`

#2. Extracting preview(single) image for video
`ffmpeg -i #{path_to_video} -f image2 -ss 1 -vframes 1 #{path_to_video}/preview_0000.jpg`

#3. Extracting images from a video for a duration
`ffmpeg -i #{path_to_video}  -r 25 -sameq -t #{duration} -s #{resolution} -vf -ss #{start_point} #{IMAGE_FILES_PATH}prefix_%d.jpeg`

#4. Trimming/cutting a video 
`ffmpeg -sameq -ss #{start_point} -t #{duration} -i #{input_vdo} #{output_vdo}`

#5. Converting to MP4
`ffmpeg -i #{input_vdo} -r 25 -y -sameq -vcodec libx264 #{output_vdo}`# here output video path extension should be .mp4

# path_to_video should be path to your video
# duration is defined in seconds
# start_point starting point in seconds
# resolution in 'digitxdigit'format