some_ffmpeg_helpers.sh

# 1. Copy from beginning to -t time (seconds) or time (00:00:00)
ffmpeg -i file_name.mp4 \
-t 00:00:00 \
-c copy \
new_file_name_1.mp4

# 2. Copy from time -ss (00:00:00) to end
ffmpeg -i file_name.mp4 \
-ss 00:00:00 \
-c copy \
new_file_name_2.mp4

# 3. Copy from time -ss (00:00:00) to -to (00:00:00) 
ffmpeg -i file_name.mp4 -ss 00:00:00 \
-to 00:00:00 \
-c copy \
new_file_name_3.mp4

# concatonate videos
# files.txt is a list of of the files to concat
# files.txt example:
# file 'file 1.mkv'
# file 'file 2.mkv'
ffmpeg -f concat -safe 0 -i files.txt -c copy output.webm

# get duration of video
ffmpeg -i file.webm 2>&1 | grep 'Duration' | cut -d ',' -f 1

# Accurate frame cutting
# http://www.markbuckler.com/post/cutting-ffmpeg/ 
ffmpeg -i file_name.webm -ss 00:00:00 -strict -2 -to 00:00:00 new_file_name.webm

# Remove audio when cutting
ffmpeg -i file_name.webm -ss 00:00:00 -strict -2 -to 00:00:00 -an new_file_name.webm

# Record audio only
ffmpeg -f alsa -i default audio.wav

# add audio and video together
ffmpeg -i video.webm -i audio.ogg -map 0:v -map 1:a -c copy audio_video.webm