support volume adjustments

edit.py

@@ -245,6 +245,7 @@ if __name__ == '__main__':
                         'resolution': info['resolution'],
                         'in': stream_in,
                         'out': stream_out,
+                        'volume': clip.get('volume', 1),
                     })
                     if 'path' in info:
                         videos[-1]['path'] = os.path.join(prefix, info['path'])

ffmpeg.py

@@ -115,6 +115,10 @@ for clip in edit:
         else:
             aid = src_info['audio'][0]['id']
             audio = []
+            if clip.get('volume', 1) != 1:
+                audio += [
+                    '-filter:a', 'volume=%s' % clip['volume']
+                ]
             audio_map = ['-map', '0:%s,0:0' % aid, '-map', '0:%s,0:1' % vid]
         cmd = [
             'ffmpeg',