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I'm copying a video from a camera stream using a command cat /dev/video0 > file.mpeg
This works perfectly, however I want too break up the file into smaller chunks... So I've been waiting pressing Ctrl+C.. Wanted to automate that so created a batch script that will wait X minutes then halt the job, meanwhile show a progress bar. Works great however I want to take it another step.. I have an XML file that contains the exact times and file names, I have a mono program that parses this file.

Here's the question.. How can I programmatically run this cat command. Sure I could execute a system command. But I was thinking of just doing the entire application in the same language. I can open a file to write as a binary write and read say 1000 bytes at a time... But what is cat doing? Does it know how much/ how fast to read somehow?

Wait with sleep and kill cat

Since it works well enough with cat and ctrl+c, the following shellscript should work.

The cat process has the process ID pid, which is used by the kill command.

#!/bin/bash



if [ $# -ne 3 ]

then

 echo "Usage: $0 <stream device> <output file> <play-time>"

 exit

fi



stream="$1"

outfile="$2"

ptime="$3"  # seconds



cat "$stream" > "$outfile" & pid=$!



sleep "$ptime"



kill $pid

cat is a simple tool for reading/writing data. There is no way to set the speed or time interval for the data transfer in cat. You have to control it outside cat. But there are many other tools.

Use the built-in features in ffmpeg

It is also possible to use the multimedia tool ffmpeg. There is a steep learning curve, but when you get into using it, you will find that it is a very powerful tool. There are detailed instructions in the manual man ffmpeg but it is better to search for a suitable tutorial via the internet.

Example:

I have tested the following command line with conversion from an MTS file to an mpeg file. I have not tested it from a device, but I think it will work. You may want to control the conversion (to be different from the defaults) using more options in the command line.

ffmpeg -t 5 -i /dev/video0 file.mpeg

where -t 5 means that 5 seconds are recorded.