delay is a shell command introducing a constant delay between its standard input and its standard output.

Usage

delay [-b <dtbufsize>] <delay>

dtbufsize is the buffer size storing the data until it has been written to stdout, in bytes.

The following modifiers are accepted:

• 12k means 12Kb (12×1024)
• 12m means 12Mb (12×1024²)
• 12g means 12Gb (12×1024³)

The parameter argument can be given with or without space (-b12m is equivalent to -b 12m).

delay is the desired delay, in milliseconds:

• 12s means 12 seconds (12×1000)
• 12m means 12 minutes (12×60×1000)
• 12h means 12 hours (12×60×60×1000)

The maximum expected bitrate provided by delay is the buffersize divided by the delay. For instance, delay -b 10m 5s will provide a maximum bitrate of 2Mb/s.

Example

To delay the output of command_A to command_B by 5 seconds:

command_A | delay 5s | command_B

If we need a 10Mb buffer:

command_A | delay -b10m 5s | command_B

As an illustration, the following command produces an input at several rates, and prints the result, delayed by 1 second, tabulated:

{ for i in {1..15}; do sleep $(bc <<< "scale=1;$i/10"); echo $i; done } |
    tee /dev/stderr | sed -u 's/^/\t/' | delay 1s

The following command allows a live-delayed video stream: it captures the webcam and encodes the result in mpeg2, which is played in vlc with a delay of 2 seconds:

ffmpeg -an -s 320x240 -f video4linux2 -i /dev/video0 -f mpeg2video -b 1M - |
    delay 2s | vlc -

Blog post

http://blog.rom1v.com/2014/01/lecture-differee-de-la-webcam-dun-raspberry-pi/ (in French)