Added ffmpeg fallback when avconv is not available

On some distros, avconv isn't available yet.
This fix adds a fallback to ffmpeg.
When none is found, no error message is displayed in the console any
more.

Fixes #5745

Also, this now uses exec() instead of shell_exec() to be able to get the
return code.

The binary path found with "which" is now used to prevent further FS
binary lookup when running the commands.

Moved the "-ss" parameter before "-i" for ffmpeg.

lib/private/preview/movies.php

@@ -8,21 +8,37 @@
  */
 namespace OC\Preview;
 
+function findBinaryPath($program) {
+	exec('which ' . escapeshellarg($program) . ' 2> /dev/null', $output, $returnCode);
+	if ($returnCode === 0 && count($output) > 0) {
+		return escapeshellcmd($output[0]);
+	}
+	return null;
+}
+
 // movie preview is currently not supported on Windows
 if (!\OC_Util::runningOnWindows()) {
-	$isShellExecEnabled = !in_array('shell_exec', explode(', ', ini_get('disable_functions')));
-	$whichAVCONV = ($isShellExecEnabled ? shell_exec('which avconv') : '');
-	$isAVCONVAvailable = !empty($whichAVCONV);
+	$isExecEnabled = !in_array('exec', explode(', ', ini_get('disable_functions')));
+
+	if ($isExecEnabled) {
+		$avconvBinary = findBinaryPath('avconv');
+		if (!$avconvBinary) {
+			$ffmpegBinary = findBinaryPath('ffmpeg');
+		}
+	}
 
-	if($isShellExecEnabled && $isAVCONVAvailable) {
+	if($isExecEnabled && ( $avconvBinary || $ffmpegBinary )) {
 
 		class Movie extends Provider {
+			public static $avconvBinary;
+			public static $ffmpegBinary;
 
 			public function getMimeType() {
 				return '/video\/.*/';
 			}
 
 			public function getThumbnail($path, $maxX, $maxY, $scalingup, $fileview) {
+				// TODO: use proc_open() and stream the source file ?
 				$absPath = \OC_Helper::tmpFile();
 				$tmpPath = \OC_Helper::tmpFile();
 
@@ -31,20 +47,38 @@ if (!\OC_Util::runningOnWindows()) {
 				$firstmb = stream_get_contents($handle, 1048576); //1024 * 1024 = 1048576
 				file_put_contents($absPath, $firstmb);
 
-				//$cmd = 'ffmpeg -y  -i ' . escapeshellarg($absPath) . ' -f mjpeg -vframes 1 -ss 1 -s ' . escapeshellarg($maxX) . 'x' . escapeshellarg($maxY) . ' ' . $tmpPath;
-				$cmd = 'avconv -an -y -ss 1 -i ' . escapeshellarg($absPath) . ' -f mjpeg -vframes 1 ' . escapeshellarg($tmpPath);
+				if (self::$avconvBinary) {
+					$cmd = self::$avconvBinary . ' -an -y -ss 1'.
+					    ' -i ' . escapeshellarg($absPath) .
+						' -f mjpeg -vframes 1 ' . escapeshellarg($tmpPath) .
+						' > /dev/null 2>&1';
+				}
+				else {
+					$cmd = self::$ffmpegBinary . ' -y -ss 1' .
+						' -i ' . escapeshellarg($absPath) .
+						' -f mjpeg -vframes 1' .
+						' -s ' . escapeshellarg($maxX) . 'x' . escapeshellarg($maxY) .
+						' ' . $tmpPath .
+						' > /dev/null 2>&1';
+				}
 
-				shell_exec($cmd);
-
-				$image = new \OC_Image($tmpPath);
+				exec($cmd, $output, $returnCode);
 
 				unlink($absPath);
-				unlink($tmpPath);
 
-				return $image->valid() ? $image : false;
+				if ($returnCode === 0) {
+					$image = new \OC_Image($tmpPath);
+					unlink($tmpPath);
+					return $image->valid() ? $image : false;
+				}
+				return false;
 			}
 		}
 
+		// a bit hacky but didn't want to use subclasses
+		Movie::$avconvBinary = $avconvBinary;
+		Movie::$ffmpegBinary = $ffmpegBinary;
+
 		\OC\Preview::registerProvider('OC\Preview\Movie');
 	}
 }