diff --git a/pandora_client/extract.py b/pandora_client/extract.py
index a4f36ba..77a70d3 100644
--- a/pandora_client/extract.py
+++ b/pandora_client/extract.py
@@ -249,7 +249,7 @@ def video_cmd(video, target, profile, info):
             n = 1
         # mix 2 mono channels into stereo(common for fcp dv mov files)
         if len(info['audio']) == 2 \
-                and len(filter(None, [a['channels'] == 1 or None for a in info['audio']])) == 2:
+                and len(list(filter(None, [a['channels'] == 1 or None for a in info['audio']]))) == 2:
             video_settings += [
                 '-filter_complex',
                 '[0:%s][0:%s] amerge' % (info['audio'][0]['id'], info['audio'][1]['id'])