Question

I’m working on some Haskell project using FFmpeg. I need to batch create from a media folder with MP4 files and create screenshots from all of them. I got the code and am using it on a terminal in Unix. It works, but how do I make it in one line to be executed in system “xxxx” in Haskell?

If not using several system”xx”…

#/bin/sh
for i in $(ls *.mp4)
do
    ffmpeg -i $i -vframes 7 -y -ss 10 -s 150x150 -an -sameq -f image2 -r 1/5  $i%1d.jpg
done

I tried:

import System.Cmd
function = do{system "#/bin/sh";
system "for i in $(ls *.mp4)";
system "do";
system "ffmpeg -i $i -vframes 7 -y -ss 10 -s 150x150 -an -sameq -f image2 -r 1/5  $i%1d.jpg";
system "done";}

but it gives a error:

-vframes: No such file or directory
/bin/sh: Syntax error: "done" unexpected

Answer 1

Bash 4.X Solution

system "/bin/bash -c 'shopt -s globstar; for i in **.mp4; do ffmpeg -i \"$i\" -vframes 7 -y -ss 10 -s 150x150 -an -sameq -f image2 -r 1/5  \"$i\"%1d.jpg; done'"

1. You don’t need #!/bin/bash with system (don’t forget the bang !)
2. Quote your variables otherwise files with spaces in their names wont work
3. Don’t use ls like that, it will break when it comes across a file with spaces in its name

Posix Solution

system "find /some/path -type f -name \"*.mp4\" -exec sh -c 'for f; do ffmpeg -i \"$f\" -vframes 7 -y -ss 10 -s 150x150 -an -sameq -f image2 -r 1/5  \"$f%1d.jpg\"; done' _ {} +"