diff --git a/render.py b/render.py
index 9b44680..d4b3a43 100644
--- a/render.py
+++ b/render.py
@@ -14,7 +14,7 @@ import ox
 
 from .pi import random
 from .render_kdenlive import KDEnliveProject, _CACHE, get_melt
-from .utils import resolve_roman, write_if_new, format_duration
+from .utils import resolve_roman, write_if_new, format_duration, needs_update
 from .render_utils import *
 
 default_prefix = "/srv/p_for_power"
@@ -153,7 +153,7 @@ def compose(clips, fragment, target=150, base=1024, voice_over=None, options=Non
             }
         })
 
-        volume_front = '-14'
+        volume_front = '-15'
         if clip.get('volume') is not None:
             volume_front = '%0.2f' % (float(volume_front) + clip['volume'])
 
@@ -263,11 +263,11 @@ def compose(clips, fragment, target=150, base=1024, voice_over=None, options=Non
             print('%07.3f-%07.3f %07.3f' % (sub_offset, sub_offset+vo["duration"], vo["duration"]), vo["src"].split('/')[-1])
             voice_overs.append(vo)
             voc = vo.copy()
-            a, b = '5', '-1'
+            a, b = '4', '-2'
             #if options.get('stereo_downmix'):
             #    a, b = '5', '-1'
             if vo_b:
-                a, b = '3', '-3'
+                a, b = '2', '-4'
             voc['filter'] = {'volume': a}
             scene['audio-center']['A1'].append(voc)
             vo_low = vo.copy()
@@ -553,10 +553,11 @@ def render_all(options):
                 ext = '.mp4'
                 if '/audio' in timeline:
                     ext = '.wav'
+                out = '%s' % timeline.replace('.kdenlive', ext)
                 cmd = get_melt() + [
                     timeline,
                     '-quiet',
-                    '-consumer', 'avformat:%s' % timeline.replace('.kdenlive', ext),
+                    '-consumer', 'avformat:%s' % out,
                 ]
                 if ext == '.wav':
                     cmd += ['vn=1']
@@ -566,7 +567,8 @@ def render_all(options):
                         cmd += ['vcodec=h264_qsv', 'pix_fmt=nv12', 'rc=icq', 'global_quality=17']
                     elif options.get("only_keyframes"):
                         cmd += ['vcodec=libx264', 'x264opts=keyint=1', 'crf=15']
-                subprocess.call(cmd)
+                if needs_update(timeline, out):
+                    subprocess.call(cmd)
                 if ext == '.wav' and timeline.endswith('audio.kdenlive'):
                     cmd = [
                         'ffmpeg', '-y',
@@ -575,8 +577,12 @@ def render_all(options):
                         timeline.replace('.kdenlive', ext),
                         timeline.replace('.kdenlive', '.mp4')
                     ]
-                    subprocess.call(cmd)
-                    os.unlink(timeline.replace('.kdenlive', ext))
+                    wav = timeline.replace('.kdenlive', ext)
+                    mp4 = timeline.replace('.kdenlive', '.mp4')
+                    if needs_update(wav, mp4):
+                        subprocess.call(cmd)
+                    if not options.get("keep_parts"):
+                        os.unlink(wav)
 
             cmds = []
             fragment_prefix = Path(fragment_prefix)
@@ -667,10 +673,11 @@ def render_all(options):
                     "vocals.wav",
                     "foley.wav"
                 ]
-            for fn in cleanup:
-                fn = fragment_prefix / fn
-                if os.path.exists(fn):
-                    os.unlink(fn)
+            if not options.get("keep_parts"):
+                for fn in cleanup:
+                    fn = fragment_prefix / fn
+                    if os.path.exists(fn):
+                        os.unlink(fn)
 
     if is_new and options["single_file"]:
         cmds = []
@@ -698,21 +705,25 @@ def render_all(options):
                     cmd += ['vcodec=h264_qsv', 'pix_fmt=nv12', 'rc=icq', 'global_quality=17']
                 elif options.get("only_keyframes"):
                     cmd += ['vcodec=libx264', 'x264opts=keyint=1', 'crf=15']
-            cmds.append(cmd)
+            if needs_update(timelines[0], out):
+                cmds.append(cmd)
+
         for src, out1, out2 in (
             ("audio-front.wav", "fl.wav", "fr.wav"),
             ("audio-center.wav", "fc.wav", "lfe.wav"),
             ("audio-rear.wav", "bl.wav", "br.wav"),
         ):
-            cmds.append([
-                "ffmpeg", "-y",
-                "-nostats", "-loglevel", "error",
-                "-i", base_prefix / src,
-                "-filter_complex",
-                "[0:0]pan=1|c0=c0[left]; [0:0]pan=1|c0=c1[right]",
-                "-map", "[left]", base_prefix / out1,
-                "-map", "[right]", base_prefix / out2,
-            ])
+            if needs_update(src, out1):
+                cmds.append([
+                    "ffmpeg", "-y",
+                    "-nostats", "-loglevel", "error",
+                    "-i", base_prefix / src,
+                    "-filter_complex",
+                    "[0:0]pan=1|c0=c0[left]; [0:0]pan=1|c0=c1[right]",
+                    "-map", "[left]", base_prefix / out1,
+                    "-map", "[right]", base_prefix / out2,
+                ])
+
         cmds.append([
             "ffmpeg", "-y",
             "-nostats", "-loglevel", "error",
diff --git a/utils.py b/utils.py
index bd1cb21..0e697fb 100644
--- a/utils.py
+++ b/utils.py
@@ -42,6 +42,15 @@ def remove_deselected_files():
         if changed:
             i.save()
 
+def needs_update(src, out):
+    mtime_src = os.lstat(src).st_mtime
+    mtime_out = os.lstat(out).st_mtime
+    #print("compare", src, out)
+    #print("ts", mtime_src, mtime_out, mtime_src > mtime_out)
+    if not os.path.exists(out) or mtime_src > mtime_out:
+        return True
+    return False
+
 def write_if_new(path, data, mode=''):
     read_mode = 'r' + mode
     write_mode = 'w' + mode