PHP exec to convert all files in directory using ffmpeg

How do i loop thru video files in a directory with extension .flv and use exec to convert each one of them (one at a time ) to mpg using ffmpeg -i original.avi final.mpg

While current file is converting, the next filename in the array should wait until exec process is complete before moving on and converting other filename in the array.

I know i can 开发者_如何学Gouse scandir($dir) to make an array of all filenames, then maybe use split to only target .flv files. Is this the best way to do it. If i use a while loop to run thru each filename and do an exec on it, how do i make sure exec file is fully converted before moving on to the next file in the array.

$dir='/path/to/dir';
$bash_commands = 'cd "'. $dir .'"
for i in *.flv; do 
    OUTFILE=$(basename "$i" .flv).mpg
    ffmpeg -i "$i" -f mpg "$OUTFILE"
done';
exec($bash_commands);

BASH code explanation:

1. The first line changes the current working directory with the command cd.
   Refer: Moving around the filesystem @ tldp.org
2. The second line starts a for loop that repeats the code inside it, while the $i variable contains the name of a file from the current working directory that is of the following pattern: *.flv. Each iteration changes the value of $i to the next file name in the current working directory.
   Refer: The for loop @ tldp.org and Loops @ tldp.org.
3. The third line assigns the value $(basename "$i" .flv).mpg to the variable named OUTFILE.
   Refer: Subshells @ tldp.org, basename @ tlpd.org and Command Substitution @ tlpd.org.
4. The fourth line initiates ffmpeg and tells it to convert the file in $i to a file named like $i, but with it's suffix changed to "mpg" instead of "flv". (The "suffix change" is done in the third line)
5. The fifth line ends the for loop.

The following should be the PHP equivalent:

chdir('/path/to/current/working/dir');
foreach (glob("*.flv") as $filename) {
    $OUTFILE = substr($filename, 0, -3) . 'mpg';
    exec('ffmpeg -i "'.$filename.'" -f mpg "'.$OUTFILE.'"');
}

Refer: glob(), chdir() and substr().