Add ffmpeg example

Inspired by https://aoeex.com/phile/php-fibers-a-practical-example/

examples/ffmpeg.php

@@ -0,0 +1,43 @@
+<?php
+
+use Amp\Pipeline\Pipeline;
+use Amp\Process\Process;
+use function Amp\ByteStream\getStdout;
+
+require dirname(__DIR__) . "/vendor/autoload.php";
+
+$ffmpeg = getenv('FFMPEG_BIN') ?: 'ffmpeg';
+$concurrency = $argv[1] ?? 3;
+$start = microtime(true);
+
+Pipeline::fromIterable(new DirectoryIterator('.'))
+ ->concurrent(3)
+ ->filter(fn ($item) => $item->getExtension() === 'php')
+ ->map(fn ($item) => createVideoClip($ffmpeg, $item->getPathname(), getTempDestination()))
+ ->forEach(fn ($result) => getStdout()->write('Successfully created clip from ' . $result[0] . ' => ' . $result[1] . PHP_EOL));
+
+$end = microtime(true);
+echo 'Directory processed in ' . round($end - $start, 1) . ' seconds' . PHP_EOL;
+
+function getTempDestination(): string
+{
+ $destination = tempnam(sys_get_temp_dir(), 'video');
+ unlink($destination);
+ $dir = dirname($destination);
+ $file = basename($destination, '.tmp');
+
+ return $dir . DIRECTORY_SEPARATOR . $file . '.mp4';
+}
+
+function createVideoClip(string $ffmpeg, string $source, string $destination): array
+{
+ $cmd = sprintf('%s -threads 1 -i %s -t 30 -crf 26 -c:v h264 -c:a ac3 %s', $ffmpeg, $source, $destination);
+
+ $success = Process::start($cmd)->join() === 0;
+
+ if ($success) {
+ return [$source, $destination];
+ } else {
+ throw new \RuntimeException('Unable to perform conversion');
+ }
+}