What security considerations should be taken into account when using ffmpeg with shell_exec() in PHP for generating thumbnails?

When using ffmpeg with shell_exec() in PHP for generating thumbnails, it is important to consider security risks such as command injections. To mitigate this risk, it is recommended to sanitize user inputs and validate the input file to prevent malicious commands from being executed.

// Sanitize user input
$inputFile = escapeshellarg($userInputFile);

// Validate input file
if (file_exists($inputFile)) {
    // Execute ffmpeg command to generate thumbnail
    $output = shell_exec("ffmpeg -i $inputFile -ss 00:00:05 -vframes 1 thumbnail.jpg");
    echo "Thumbnail generated successfully!";
} else {
    echo "Invalid input file.";
}