diff --git a/audiblez/core.py b/audiblez/core.py
index ad9ebad..d96033b 100755
--- a/audiblez/core.py
+++ b/audiblez/core.py
@@ -174,6 +174,18 @@ def gen_audio_segments(pipeline, text, voice, speed, stats=None, max_sentences=N
     return audio_segments
 
 
+def gen_text(text, voice='af_heart', output_file='text.wav', speed=1, play=False):
+    lang_code = voice[:1]
+    pipeline = KPipeline(lang_code=lang_code)
+    load_spacy()
+    audio_segments = gen_audio_segments(pipeline, text, voice=voice, speed=speed);
+    final_audio = np.concatenate(audio_segments)
+    soundfile.write(output_file, final_audio, sample_rate)
+    if play:
+        subprocess.run(['ffplay', '-autoexit', '-nodisp', output_file])
+
+
+
 def find_document_chapters_and_extract_texts(book):
     """Returns every chapter that is an ITEM_DOCUMENT and enriches each chapter with extracted_text."""
     document_chapters = []
@@ -253,7 +265,7 @@ def create_m4b(chapter_files, filename, cover_image, output_folder):
             audio = AudioSegment.from_wav(wav_file)
             combined_audio += audio
         print('Converting to Mp4...')
-        combined_audio.export(tmp_file_path, format="mp4", codec="aac", bitrate="128k")
+        combined_audio.export(tmp_file_path, format="mp4", bitrate="128k")
     final_filename = Path(output_folder) / filename.replace('.epub', '.m4b')
     print('Creating M4B file...')
 
diff --git a/audiblez/ui.py b/audiblez/ui.py
index 6c838cb..43afcf8 100644
--- a/audiblez/ui.py
+++ b/audiblez/ui.py
@@ -495,7 +495,7 @@ class MainWindow(wx.Frame):
             tmp_preview_wav_file = NamedTemporaryFile(suffix='.wav', delete=False)
             soundfile.write(tmp_preview_wav_file, final_audio, core.sample_rate)
             cmd = ['ffplay', '-autoexit', '-nodisp', tmp_preview_wav_file.name]
-            subprocess.Popen(' '.join(cmd), stdout=subprocess.PIPE, shell=True, preexec_fn=os.setsid)
+            subprocess.run(cmd)
             button.SetLabel("🔊 Preview")
             button.Enable()
 
diff --git a/test/test_main.py b/test/test_main.py
index 2a84d31..638b3d8 100644
--- a/test/test_main.py
+++ b/test/test_main.py
@@ -2,11 +2,13 @@ import os
 import unittest
 from pathlib import Path
 
-from audiblez.core import main
+from ebooklib import epub
+
+from audiblez.core import main, find_document_chapters_and_extract_texts
 
 
 class MainTest(unittest.TestCase):
-    def base(self, name, url, **kwargs):
+    def base(self, name, url='', **kwargs):
         if not Path(f'{name}.epub').exists():
             os.system(f'wget {url} -O {name}.epub')
         Path(f'{name}.m4b').unlink(missing_ok=True)
@@ -42,3 +44,9 @@ class MainTest(unittest.TestCase):
     def test_chinese(self):
         url = 'https://www.gutenberg.org/ebooks/24225.epub3.images'
         self.base('chinese', url, voice='zf_xiaobei')
+
+    def test_leigh(self):
+        book = epub.read_epub('leigh.epub')
+        document_chapters = find_document_chapters_and_extract_texts(book)
+        chapters = [c for c in document_chapters if c.get_name() == 'Text/Chap07.xhtml']
+        self.base('leigh', voice='af_heart', selected_chapters=chapters, max_sentences=5)