diff --git a/build b/build
index a249cd2..00e6458 100755
--- a/build
+++ b/build
@@ -1,3 +1,3 @@
 #!/bin/sh
-rm -f dist/m4b-tool* bin/m4b-tool_*.log
+rm -f dist/m4b-tool* bin/*.log
 php -d phar.readonly=off tools/box.phar build && chmod +x dist/*.phar && tar -C dist -czf dist/m4b-tool.tar.gz m4b-tool.phar && cd dist && zip m4b-tool.zip m4b-tool.phar && cd -
diff --git a/src/library/M4bTool/Audio/MetaDataHandler.php b/src/library/M4bTool/Audio/MetaDataHandler.php
index 87004c2..35feda5 100644
--- a/src/library/M4bTool/Audio/MetaDataHandler.php
+++ b/src/library/M4bTool/Audio/MetaDataHandler.php
@@ -25,6 +25,10 @@ class MetaDataHandler implements TagReaderInterface, TagWriterInterface, Duratio
     const FORMAT_MP3 = "mp3";
 
 
+    const CODEC_MP3 = "mp3";
+    const CODEC_AAC = "aac";
+    const CODEC_ALAC = "alac";
+
     const EXTENSION_FORMAT_MAPPING = [
         self::EXTENSION_M4A => self::FORMAT_MP4,
         self::EXTENSION_M4B => self::FORMAT_MP4,
@@ -57,10 +61,6 @@ public function estimateDuration(SplFileInfo $file): ?TimeUnit
         return $this->ffmpeg->estimateDuration($file);
     }
 
-    public function detectExactDuration(SplFileInfo $file)
-    {
-
-    }
 
     public function detectFormat(SplFileInfo $file)
     {
@@ -79,10 +79,6 @@ private static function getFormatByExtension(SplFileInfo $file)
     }
 
 
-//    public function detectCodec(SplFileInfo $file) {
-//
-//    }
-
     public function loadTag(SplFileInfo $file)
     {
 
diff --git a/src/library/M4bTool/Command/MergeCommand.php b/src/library/M4bTool/Command/MergeCommand.php
index d15aa7e..f64aa38 100644
--- a/src/library/M4bTool/Command/MergeCommand.php
+++ b/src/library/M4bTool/Command/MergeCommand.php
@@ -15,11 +15,13 @@
 use M4bTool\Audio\Chapter;
 use M4bTool\Audio\Silence;
 use M4bTool\Executables\Ffmpeg;
+use M4bTool\Executables\FileConverterOptions;
 use M4bTool\Executables\Mp4art;
 use M4bTool\Executables\Mp4chaps;
 use M4bTool\Executables\Mp4info;
 use M4bTool\Executables\Mp4tags;
 use M4bTool\Executables\Mp4v2Wrapper;
+use M4bTool\Executables\Tasks\ConversionTask;
 use M4bTool\Filesystem\DirectoryLoader;
 use M4bTool\Chapter\ChapterMarker;
 use M4bTool\Parser\FfmetaDataParser;
@@ -49,6 +51,7 @@ class MergeCommand extends AbstractConversionCommand implements MetaReaderInterf
     const OPTION_NO_CONVERSION = "no-conversion";
     const OPTION_BATCH_PATTERN = "batch-pattern";
     const OPTION_DRY_RUN = "dry-run";
+    const OPTION_JOBS = "jobs";
 
 
     const MAPPING_OPTIONS_PLACEHOLDERS = [
@@ -130,6 +133,7 @@ protected function configure()
 
         $this->addOption(static::OPTION_BATCH_PATTERN, null, InputOption::VALUE_OPTIONAL | InputOption::VALUE_IS_ARRAY, "multiple batch patterns that can be used to merge all audio books in a directory matching the given patterns (e.g. %a/%t for author/title)", []);
         $this->addOption(static::OPTION_DRY_RUN, null, InputOption::VALUE_NONE, "perform a dry run without converting all the files in batch mode (requires --" . static::OPTION_BATCH_PATTERN . ")");
+        $this->addOption(static::OPTION_JOBS, null, InputOption::VALUE_OPTIONAL, "Specifies the number of jobs (commands) to run simultaneously", 1);
 
     }
 
@@ -603,22 +607,6 @@ private function prepareMergeWithoutConversion()
         }
     }
 
-    /**
-     * @return string
-     * @throws Exception
-     */
-    private function createOutputTempDir()
-    {
-        $dir = $this->outputFile->getPath() ? $this->outputFile->getPath() . DIRECTORY_SEPARATOR : "";
-        $dir .= $this->outputFile->getBasename("." . $this->outputFile->getExtension()) . "-tmpfiles" . DIRECTORY_SEPARATOR;
-
-        if (!is_dir($dir) && !mkdir($dir, 0755, true)) {
-            $message = sprintf("Could not create temp directory %s", $dir);
-            $this->debug($message);
-            throw new Exception($message);
-        }
-        return $dir;
-    }
     /**
      * @throws InvalidArgumentException
      * @throws Exception
@@ -629,50 +617,175 @@ private function convertInputFiles()
         $this->adjustBitrateForIpod($this->filesToConvert);
 
         $coverTargetFile = new SPLFileInfo($this->argInputFile . "/cover.jpg");
-        $forceExtractCover = $this->optForce;
+
+
         $baseFdkAacCommand = $this->buildFdkaacCommand();
 
+        $firstFile = reset($this->filesToConvert);
+        if ($firstFile) {
+            $this->extractCover($firstFile, $coverTargetFile, $this->optForce);
+        }
+
         $outputTempDir = $this->createOutputTempDir();
-        foreach ($this->filesToConvert as $index => $file) {
 
-            // use "force" flag only once
-            $this->extractCover($file, $coverTargetFile, $forceExtractCover);
-            $forceExtractCover = false;
+        if ($baseFdkAacCommand) {
+            foreach ($this->filesToConvert as $index => $file) {
 
-            $pad = str_pad($index + 1, $padLen, "0", STR_PAD_LEFT);
-            $outputFile = new SplFileInfo($outputTempDir . $pad . '-' . $file->getBasename("." . $file->getExtension()) . "-converting." . $this->optAudioExtension);
-            $finishedOutputFile = new SplFileInfo($outputTempDir . $pad . '-' . $file->getBasename("." . $file->getExtension()) . "-finished." . $this->optAudioExtension);
+                $pad = str_pad($index + 1, $padLen, "0", STR_PAD_LEFT);
+                $outputFile = new SplFileInfo($outputTempDir . $pad . '-' . $file->getBasename("." . $file->getExtension()) . "-converting." . $this->optAudioExtension);
+                $finishedOutputFile = new SplFileInfo($outputTempDir . $pad . '-' . $file->getBasename("." . $file->getExtension()) . "-finished." . $this->optAudioExtension);
 
-            $this->filesToMerge[] = $finishedOutputFile;
+                $this->filesToMerge[] = $finishedOutputFile;
 
-            if ($outputFile->isFile()) {
-                unlink($outputFile);
-            }
+                if ($outputFile->isFile()) {
+                    unlink($outputFile);
+                }
 
-            if ($finishedOutputFile->isFile() && $finishedOutputFile->getSize() > 0) {
-                $this->notice("output file " . $outputFile . " already exists, skipping");
-                continue;
+                if ($finishedOutputFile->isFile() && $finishedOutputFile->getSize() > 0) {
+                    $this->notice("output file " . $outputFile . " already exists, skipping");
+                    continue;
+                }
+
+
+                if ($baseFdkAacCommand) {
+                    $this->otherTmpFiles[] = $this->executeFdkaacCommand($baseFdkAacCommand, $file, $outputFile);
+                } else {
+                    $this->executeFfmpegCommand($file, $outputFile);
+                }
+
+
+                if (!$outputFile->isFile()) {
+                    throw new Exception("could not convert " . $file . " to " . $outputFile);
+                }
+
+                if ($outputFile->getSize() == 0) {
+                    unlink($outputFile);
+                    throw new Exception("could not convert " . $file . " to " . $outputFile);
+                }
+
+                rename($outputFile, $finishedOutputFile);
             }
+        } else {
+            $ffmpeg = new Ffmpeg();
+            /** @var ConversionTask[] $conversionTasks */
+            $conversionTasks = [];
 
+            foreach ($this->filesToConvert as $index => $file) {
 
-            if ($baseFdkAacCommand) {
-                $this->otherTmpFiles[] = $this->executeFdkaacCommand($baseFdkAacCommand, $file, $outputFile);
-            } else {
-                $this->executeFfmpegCommand($file, $outputFile);
+                $pad = str_pad($index + 1, $padLen, "0", STR_PAD_LEFT);
+                $outputFile = new SplFileInfo($outputTempDir . $pad . '-' . $file->getBasename("." . $file->getExtension()) . "-converting." . $this->optAudioExtension);
+                $finishedOutputFile = new SplFileInfo($outputTempDir . $pad . '-' . $file->getBasename("." . $file->getExtension()) . "-finished." . $this->optAudioExtension);
+
+                $this->filesToMerge[] = $finishedOutputFile;
+
+                if ($outputFile->isFile()) {
+                    unlink($outputFile);
+                }
+
+
+                $options = new FileConverterOptions();
+                $options->source = $file;
+                $options->destination = $outputFile;
+                $options->tempDir = $outputTempDir;
+                $options->extension = $this->optAudioExtension;
+                $options->codec = $this->optAudioCodec;
+                $options->format = $this->optAudioFormat;
+                $options->channels = $this->optAudioChannels;
+                $options->sampleRate = $this->optAudioSampleRate;
+                $options->bitRate = $this->optAudioBitRate;
+                $options->force = $this->optForce;
+
+                $conversionTasks[] = new ConversionTask($ffmpeg, $options);
             }
 
+            $jobs = $this->input->getOption(static::OPTION_JOBS) ? (int)$this->input->getOption(static::OPTION_JOBS) : 1;
+
+            // minimum 1 job, maximum count conversionTasks jobs
+            $jobs = max(min($jobs, count($conversionTasks)), 1);
+
+            $runningTaskCount = 0;
+            $conversionTaskQueue = $conversionTasks;
+            $runningTasks = [];
+            $start = microtime(true);
+            $increaseProgressBarSeconds = 5;
+            do {
+                $firstFailedTask = null;
+                if ($runningTaskCount > 0 && $firstFailedTask === null) {
+                    foreach ($runningTasks as $task) {
+                        if ($task->didFail()) {
+                            $firstFailedTask = $task;
+                            break;
+                        }
+                    }
+                }
+
+                // add new tasks, if no task did fail and jobs left
+                /** @var ConversionTask $task */
+                $task = null;
+                while ($firstFailedTask === null && $runningTaskCount < $jobs && $task = array_shift($conversionTaskQueue)) {
+                    $task->run();
+                    $runningTasks[] = $task;
+                    $runningTaskCount++;
+                }
+
+                usleep(250000);
+
+                $runningTasks = array_filter($runningTasks, function (ConversionTask $task) {
+                    return $task->isRunning();
+                });
+
+                $runningTaskCount = count($runningTasks);
+                $conversionQueueLength = count($conversionTaskQueue);
 
-            if (!$outputFile->isFile()) {
-                throw new Exception("could not convert " . $file . " to " . $outputFile);
+                $time = microtime(true);
+                $progressBar = str_repeat("+", ceil(($time - $start) / $increaseProgressBarSeconds));
+                $this->output->write(sprintf("\r%d/%d remaining tasks running: %s", $runningTaskCount, ($conversionQueueLength + $runningTaskCount), $progressBar), false, OutputInterface::VERBOSITY_VERBOSE);
+
+            } while ($conversionQueueLength > 0 || $runningTaskCount > 0);
+            $this->output->writeln("", OutputInterface::VERBOSITY_VERBOSE);
+            /** @var ConversionTask $firstFailedTask */
+            if ($firstFailedTask !== null) {
+                throw new Exception("a task has failed", null, $firstFailedTask->getLastException());
             }
 
-            if ($outputFile->getSize() == 0) {
-                unlink($outputFile);
-                throw new Exception("could not convert " . $file . " to " . $outputFile);
+
+            /** @var ConversionTask $task */
+            foreach ($conversionTasks as $index => $task) {
+                $pad = str_pad($index + 1, $padLen, "0", STR_PAD_LEFT);
+                $file = $task->getOptions()->source;
+                $outputFile = $task->getOptions()->destination;
+                $finishedOutputFile = new SplFileInfo($outputTempDir . $pad . '-' . $file->getBasename("." . $file->getExtension()) . "-finished." . $this->optAudioExtension);
+
+                if (!$outputFile->isFile()) {
+                    throw new Exception("could not convert " . $file . " to " . $outputFile);
+                }
+
+                if ($outputFile->getSize() == 0) {
+                    unlink($outputFile);
+                    throw new Exception("could not convert " . $file . " to " . $outputFile);
+                }
+
+                rename($outputFile, $finishedOutputFile);
             }
+        }
+
+    }
 
-            rename($outputFile, $finishedOutputFile);
+    /**
+     * @return string
+     * @throws Exception
+     */
+    private function createOutputTempDir()
+    {
+        $dir = $this->outputFile->getPath() ? $this->outputFile->getPath() . DIRECTORY_SEPARATOR : "";
+        $dir .= $this->outputFile->getBasename("." . $this->outputFile->getExtension()) . "-tmpfiles" . DIRECTORY_SEPARATOR;
+
+        if (!is_dir($dir) && !mkdir($dir, 0755, true)) {
+            $message = sprintf("Could not create temp directory %s", $dir);
+            $this->debug($message);
+            throw new Exception($message);
         }
+        return $dir;
     }
 
     /**
@@ -798,46 +911,6 @@ private function mergeFiles()
         return $outputTempFile;
     }
 
-    private function deleteTemporaryFiles()
-    {
-        if ($this->optDebug) {
-            return;
-        }
-
-        if ($this->input->getOption(static::OPTION_NO_CONVERSION)) {
-            return;
-        }
-
-        try {
-            $this->deleteFilesAndParentDir($this->filesToMerge);
-            $this->deleteFilesAndParentDir($this->otherTmpFiles);
-        } catch (Throwable $e) {
-            $this->error("could not delete temporary files: ", $e->getMessage());
-            $this->debug("trace:", $e->getTraceAsString());
-        }
-
-    }
-
-    private function deleteFilesAndParentDir(array $files)
-    {
-        $file = null;
-        foreach ($files as $file) {
-            unlink($file);
-        }
-        if ($file === null) {
-            return true;
-        }
-        $parentDir = dirname($file);
-        $recIt = new RecursiveDirectoryIterator($parentDir, FilesystemIterator::SKIP_DOTS);
-        $it = new IteratorIterator($recIt);
-        $filesToDelete = iterator_to_array($it);
-        if (count($filesToDelete) > 0) {
-            return false;
-        }
-        rmdir($parentDir);
-        return true;
-    }
-
     /**
      * @param SplFileInfo $outputFile
      * @throws InvalidArgumentException
@@ -909,5 +982,45 @@ private function moveFinishedOutputFile(SplFileInfo $outputTempFile, SplFileInfo
         }
     }
 
+    private function deleteTemporaryFiles()
+    {
+        if ($this->optDebug) {
+            return;
+        }
+
+        if ($this->input->getOption(static::OPTION_NO_CONVERSION)) {
+            return;
+        }
+
+        try {
+            $this->deleteFilesAndParentDir($this->filesToMerge);
+            $this->deleteFilesAndParentDir($this->otherTmpFiles);
+        } catch (Throwable $e) {
+            $this->error("could not delete temporary files: ", $e->getMessage());
+            $this->debug("trace:", $e->getTraceAsString());
+        }
+
+    }
+
+    private function deleteFilesAndParentDir(array $files)
+    {
+        $file = null;
+        foreach ($files as $file) {
+            unlink($file);
+        }
+        if ($file === null) {
+            return true;
+        }
+        $parentDir = dirname($file);
+        $recIt = new RecursiveDirectoryIterator($parentDir, FilesystemIterator::SKIP_DOTS);
+        $it = new IteratorIterator($recIt);
+        $filesToDelete = iterator_to_array($it);
+        if (count($filesToDelete) > 0) {
+            return false;
+        }
+        rmdir($parentDir);
+        return true;
+    }
+
 
 }
diff --git a/src/library/M4bTool/Executables/AbstractExecutable.php b/src/library/M4bTool/Executables/AbstractExecutable.php
index 83b9559..2b76d9b 100644
--- a/src/library/M4bTool/Executables/AbstractExecutable.php
+++ b/src/library/M4bTool/Executables/AbstractExecutable.php
@@ -42,12 +42,18 @@ public function __construct($pathToBinary, ProcessHelper $processHelper = null,
     }
 
 
-    protected function createProcess(array $arguments, $messageInCaseOfError = null)
+    protected function runProcess(array $arguments, $messageInCaseOfError = null)
     {
         array_unshift($arguments, $this->pathToBinary);
         return $this->processHelper->run($this->output, $arguments, $messageInCaseOfError);
     }
 
+    protected function createNonBlockingProcess(array $arguments)
+    {
+        array_unshift($arguments, $this->pathToBinary);
+        return new Process($arguments);
+    }
+
     protected function appendParameterToCommand(&$command, $parameterName, $parameterValue = null)
     {
         if (is_bool($parameterValue)) {
diff --git a/src/library/M4bTool/Executables/Fdkaac.php b/src/library/M4bTool/Executables/Fdkaac.php
new file mode 100644
index 0000000..1ae5a12
--- /dev/null
+++ b/src/library/M4bTool/Executables/Fdkaac.php
@@ -0,0 +1,84 @@
+<?php
+
+
+namespace M4bTool\Executables;
+
+
+use Exception;
+use M4bTool\Audio\Tag;
+use M4bTool\Common\Flags;
+use Sandreas\Time\TimeUnit;
+use SplFileInfo;
+use Symfony\Component\Console\Helper\ProcessHelper;
+use Symfony\Component\Console\Output\OutputInterface;
+use Symfony\Component\Process\Process;
+
+class Fdkaac extends AbstractExecutable implements TagReaderInterface, TagWriterInterface, DurationDetectorInterface, FileConverterInterface
+{
+    public function __construct($pathToBinary = "fdkaac", ProcessHelper $processHelper = null, OutputInterface $output = null)
+    {
+        parent::__construct($pathToBinary, $processHelper, $output);
+    }
+
+
+    /**
+     * @param SplFileInfo $file
+     * @return TimeUnit|null
+     * @throws Exception
+     */
+    public function estimateDuration(SplFileInfo $file): ?TimeUnit
+    {
+        throw new Exception("not implemented");
+    }
+
+    /**
+     * @param SplFileInfo $file
+     * @return TimeUnit|null
+     * @throws Exception
+     */
+    public function inspectExactDuration(SplFileInfo $file): ?TimeUnit
+    {
+        throw new Exception("not implemented");
+    }
+
+    /**
+     * @param SplFileInfo $file
+     * @return Tag
+     * @throws Exception
+     */
+    public function readTag(SplFileInfo $file): Tag
+    {
+        throw new Exception("not implemented");
+    }
+
+    /**
+     * @param SplFileInfo $file
+     * @param Tag $tag
+     * @param Flags $flags
+     * @return mixed
+     * @throws Exception
+     */
+    public function writeTag(SplFileInfo $file, Tag $tag, Flags $flags = null)
+    {
+        throw new Exception("not implemented");
+    }
+
+    /**
+     * @param FileConverterOptions $options
+     * @return Process
+     * @throws Exception
+     */
+    public function convertFile(FileConverterOptions $options): Process
+    {
+        throw new Exception("not implemented");
+    }
+
+    /**
+     * @param FileConverterOptions $options
+     * @return bool
+     */
+    public function supportsConversion(FileConverterOptions $options): bool
+    {
+        return false;
+    }
+}
\ No newline at end of file
diff --git a/src/library/M4bTool/Executables/Ffmpeg.php b/src/library/M4bTool/Executables/Ffmpeg.php
index 23c210b..2700f76 100644
--- a/src/library/M4bTool/Executables/Ffmpeg.php
+++ b/src/library/M4bTool/Executables/Ffmpeg.php
@@ -6,6 +6,7 @@
 
 use Exception;
 use M4bTool\Audio\Chapter;
+use M4bTool\Audio\MetaDataHandler;
 use M4bTool\Audio\Tag;
 use M4bTool\Common\Flags;
 use M4bTool\Parser\FfmetaDataParser;
@@ -15,9 +16,10 @@
 use SplFileInfo;
 use Symfony\Component\Console\Helper\ProcessHelper;
 use Symfony\Component\Console\Output\OutputInterface;
+use Symfony\Component\Process\Process;
 
 
-class Ffmpeg extends AbstractExecutable implements TagReaderInterface, TagWriterInterface, DurationDetectorInterface
+class Ffmpeg extends AbstractExecutable implements TagReaderInterface, TagWriterInterface, DurationDetectorInterface, FileConverterInterface
 {
     const AAC_FALLBACK_CODEC = "aac";
     const AAC_BEST_QUALITY_NON_FREE_CODEC = "libfdk_aac";
@@ -168,7 +170,7 @@ private function quote($string)
     protected function ffmpeg($arguments)
     {
         array_unshift($arguments, "-hide_banner");
-        return $this->createProcess($arguments);
+        return $this->runProcess($arguments);
     }
 
     /**
@@ -203,27 +205,6 @@ public function loadHighestAvailableQualityAacCodec()
         return static::AAC_FALLBACK_CODEC;
     }
 
-    /**
-     * @param SplFileInfo $file
-     * @return TimeUnit|void
-     * @throws Exception
-     */
-    public function estimateDuration(SplFileInfo $file): ?TimeUnit
-    {
-        $process = $this->ffmpeg([
-            "-hide_banner",
-            "-i", $file,
-            "-f", "ffmetadata",
-            "-"]);
-        $output = $process->getOutput() . $process->getErrorOutput();
-
-        preg_match("/\bDuration:[\s]+([0-9:\.]+)/", $output, $matches);
-        if (!isset($matches[1])) {
-            return null;
-        }
-        return TimeUnit::fromFormat($matches[1], TimeUnit::FORMAT_DEFAULT);
-    }
-
     /**
      * @param SplFileInfo $file
      * @return TimeUnit|void
@@ -254,14 +235,25 @@ private function createStreamInfoProcess(SplFileInfo $file)
         ]);
     }
 
-    private function createMetaDataProcess(SplFileInfo $file)
+    /**
+     * @param SplFileInfo $file
+     * @return TimeUnit|void
+     * @throws Exception
+     */
+    public function estimateDuration(SplFileInfo $file): ?TimeUnit
     {
-        return $this->ffmpeg([
+        $process = $this->ffmpeg([
             "-hide_banner",
             "-i", $file,
             "-f", "ffmetadata",
-            "-"
-        ]);
+            "-"]);
+        $output = $process->getOutput() . $process->getErrorOutput();
+
+        preg_match("/\bDuration:[\s]+([0-9:\.]+)/", $output, $matches);
+        if (!isset($matches[1])) {
+            return null;
+        }
+        return TimeUnit::fromFormat($matches[1], TimeUnit::FORMAT_DEFAULT);
     }
 
     /**
@@ -284,6 +276,16 @@ public function readTag(SplFileInfo $file): Tag
         return $metaData->toTag();
     }
 
+    private function createMetaDataProcess(SplFileInfo $file)
+    {
+        return $this->ffmpeg([
+            "-hide_banner",
+            "-i", $file,
+            "-f", "ffmetadata",
+            "-"
+        ]);
+    }
+
     public function detectSilences(SplFileInfo $file, TimeUnit $silenceLength)
     {
         $process = $this->ffmpeg([
@@ -298,4 +300,53 @@ public function detectSilences(SplFileInfo $file, TimeUnit $silenceLength)
         return $silenceParser->parse($this->getAllProcessOutput($process));
     }
 
+
+    /**
+     * @param FileConverterOptions $options
+     * @return Process
+     */
+    public function convertFile(FileConverterOptions $options): Process
+    {
+        $inputFile = $options->source;
+        $command = [
+            "-i", $inputFile,
+            "-max_muxing_queue_size", "9999",
+            "-map_metadata", "0",
+        ];
+
+        // backwards compatibility: ffmpeg needed experimental flag in earlier versions
+        if ($options->codec == MetaDataHandler::CODEC_AAC) {
+            $command[] = "-strict";
+            $command[] = "experimental";
+        }
+
+
+        // Relocating moov atom to the beginning of the file can facilitate playback before the file is completely downloaded by the client.
+        $command[] = "-movflags";
+        $command[] = "+faststart";
+
+        // no video for files is required because chapters will not work if video is embedded and shorter than audio length
+        $command[] = "-vn";
+
+        $this->appendParameterToCommand($command, "-y", $options->force);
+        $this->appendParameterToCommand($command, "-ab", $options->bitRate);
+        $this->appendParameterToCommand($command, "-ar", $options->sampleRate);
+        $this->appendParameterToCommand($command, "-ac", $options->channels);
+        $this->appendParameterToCommand($command, "-acodec", $options->codec);
+
+        // alac can be used for m4a/m4b, but not ffmpeg says it is not mp4 compilant
+        if ($options->format && $options->codec !== MetaDataHandler::CODEC_ALAC) {
+            $this->appendParameterToCommand($command, "-f", $options->format);
+        }
+
+        $command[] = $options->destination;
+        $process = $this->createNonBlockingProcess($command);
+        $process->start();
+        return $process;
+    }
+
+    public function supportsConversion(FileConverterOptions $options): bool
+    {
+        return true;
+    }
 }
\ No newline at end of file
diff --git a/src/library/M4bTool/Executables/FileConverterInterface.php b/src/library/M4bTool/Executables/FileConverterInterface.php
new file mode 100644
index 0000000..6efa672
--- /dev/null
+++ b/src/library/M4bTool/Executables/FileConverterInterface.php
@@ -0,0 +1,17 @@
+<?php
+
+
+namespace M4bTool\Executables;
+
+
+use Symfony\Component\Process\Process;
+
+interface FileConverterInterface
+{
+
+
+    public function convertFile(FileConverterOptions $options): Process;
+
+    public function supportsConversion(FileConverterOptions $options): bool;
+
+}
\ No newline at end of file
diff --git a/src/library/M4bTool/Executables/FileConverterOptions.php b/src/library/M4bTool/Executables/FileConverterOptions.php
new file mode 100644
index 0000000..ba2814d
--- /dev/null
+++ b/src/library/M4bTool/Executables/FileConverterOptions.php
@@ -0,0 +1,28 @@
+<?php
+
+
+namespace M4bTool\Executables;
+
+
+use SplFileInfo;
+
+class FileConverterOptions
+{
+    public $codec;
+    public $force;
+    public $bitRate;
+    public $sampleRate;
+    public $channels;
+    public $format;
+    public $extension;
+
+
+    /** @var SplFileInfo */
+    public $tempDir;
+
+    /** @var SplFileInfo */
+    public $source;
+
+    /** @var SplFileInfo */
+    public $destination;
+}
\ No newline at end of file
diff --git a/src/library/M4bTool/Executables/Mp4art.php b/src/library/M4bTool/Executables/Mp4art.php
index cceaa92..8043744 100644
--- a/src/library/M4bTool/Executables/Mp4art.php
+++ b/src/library/M4bTool/Executables/Mp4art.php
@@ -31,7 +31,7 @@ public function writeTag(SplFileInfo $file, Tag $tag, Flags $flags = null)
 
         $command = ["--add", $tag->cover, $file];
         // $this->appendParameterToCommand($command, "-f", $this->optForce);
-        $process = $this->createProcess($command);
+        $process = $this->runProcess($command);
 
         if ($process->getExitCode() !== 0) {
             throw new Exception(sprintf("Could not add cover to file: %s, %s, %d", $file, $process->getOutput() . $process->getErrorOutput(), $process->getExitCode()));
diff --git a/src/library/M4bTool/Executables/Mp4chaps.php b/src/library/M4bTool/Executables/Mp4chaps.php
index 856e9b0..6b47d13 100644
--- a/src/library/M4bTool/Executables/Mp4chaps.php
+++ b/src/library/M4bTool/Executables/Mp4chaps.php
@@ -39,7 +39,7 @@ public function writeTag(SplFileInfo $file, Tag $tag, Flags $flags = null)
         file_put_contents($chaptersFile, $this->chaptersToMp4v2Format($tag->chapters));
         $command[] = "-i";
         $command[] = $file;
-        $process = $this->createProcess($command);
+        $process = $this->runProcess($command);
 
         if ($process->getExitCode() !== 0) {
             unlink($chaptersFile);
diff --git a/src/library/M4bTool/Executables/Mp4info.php b/src/library/M4bTool/Executables/Mp4info.php
index f2e0456..529e6fe 100644
--- a/src/library/M4bTool/Executables/Mp4info.php
+++ b/src/library/M4bTool/Executables/Mp4info.php
@@ -19,7 +19,7 @@ public function __construct($pathToBinary = "mp4info", ProcessHelper $processHel
 
     public function estimateDuration(SplFileInfo $file): ?TimeUnit
     {
-        $process = $this->createProcess([$file]);
+        $process = $this->runProcess([$file]);
         $output = $process->getOutput() . $process->getErrorOutput();
         preg_match("/([1-9][0-9]*\.[0-9]{3}) secs,/isU", $output, $matches);
         if (!isset($matches[1])) {
diff --git a/src/library/M4bTool/Executables/Mp4tags.php b/src/library/M4bTool/Executables/Mp4tags.php
index 26597a2..67de767 100644
--- a/src/library/M4bTool/Executables/Mp4tags.php
+++ b/src/library/M4bTool/Executables/Mp4tags.php
@@ -60,7 +60,7 @@ public function writeTag(SplFileInfo $file, Tag $tag, Flags $flags = null)
         }
 
         $command[] = $file;
-        $process = $this->createProcess($command);
+        $process = $this->runProcess($command);
 
         if ($process->getExitCode() !== 0) {
             throw new Exception(sprintf("Could not tag file: %s, %s, %d", $file, $process->getOutput() . $process->getErrorOutput(), $process->getExitCode()));
@@ -74,7 +74,7 @@ public function writeTag(SplFileInfo $file, Tag $tag, Flags $flags = null)
     private function doesMp4tagsSupportSorting()
     {
         $command = ["-help"];
-        $process = $this->createProcess($command);
+        $process = $this->runProcess($command);
         $result = $process->getOutput() . $process->getErrorOutput();
         $searchStrings = ["-sortname", "-sortartist", "-sortalbum"];
         foreach ($searchStrings as $searchString) {
diff --git a/src/library/M4bTool/Executables/Tasks/ConversionTask.php b/src/library/M4bTool/Executables/Tasks/ConversionTask.php
new file mode 100644
index 0000000..67af0a9
--- /dev/null
+++ b/src/library/M4bTool/Executables/Tasks/ConversionTask.php
@@ -0,0 +1,83 @@
+<?php
+
+
+namespace M4bTool\Executables\Tasks;
+
+
+use M4bTool\Executables\Ffmpeg;
+use M4bTool\Executables\FileConverterOptions;
+use SplFileInfo;
+use Symfony\Component\Process\Process;
+use Throwable;
+
+
+class ConversionTask implements Runnable
+{
+    /**
+     * @var Ffmpeg
+     */
+    protected $ffmpeg;
+    /**
+     * @var FileConverterOptions
+     */
+    protected $options;
+
+
+    /** @var Process */
+    protected $process;
+
+    /** @var Throwable */
+    protected $lastException;
+
+    public function __construct(Ffmpeg $ffmpeg, FileConverterOptions $options)
+    {
+        $this->ffmpeg = $ffmpeg;
+        $this->options = $options;
+        $pad = uniqid("", true);
+        $file = $this->options->source;
+        $options = clone $this->options;
+        $options->destination = new SplFileInfo($this->options->tempDir . $pad . '-' . $file->getBasename("." . $file->getExtension()) . "-converting." . $this->options->extension);
+    }
+
+    public function run()
+    {
+        try {
+            $this->lastException = null;
+            $this->process = $this->ffmpeg->convertFile($this->options);
+        } catch (Throwable $e) {
+            $this->lastException = $e;
+        }
+
+    }
+
+    public function isRunning()
+    {
+        if ($this->process) {
+            return $this->process->isRunning();
+        }
+        return false;
+    }
+
+    /**
+     * @return Process
+     */
+    public function getProcess()
+    {
+        return $this->process;
+    }
+
+    public function didFail()
+    {
+        return $this->lastException instanceof Throwable;
+    }
+
+    public function getLastException()
+    {
+        return $this->lastException;
+    }
+
+    public function getOptions()
+    {
+        return $this->options;
+    }
+}
\ No newline at end of file
diff --git a/src/library/M4bTool/Executables/Tasks/Runnable.php b/src/library/M4bTool/Executables/Tasks/Runnable.php
new file mode 100644
index 0000000..d91e719
--- /dev/null
+++ b/src/library/M4bTool/Executables/Tasks/Runnable.php
@@ -0,0 +1,10 @@
+<?php
+
+
+namespace M4bTool\Executables\Tasks;
+
+
+interface Runnable
+{
+    public function run();
+}
\ No newline at end of file