detect ffmpeg or avconv, use version from ~/.ox/bin if available

oxtimelines/ffmpeg.py

@@ -11,7 +11,14 @@ import Image
 import numpy as np
 import ox
 
-FFMPEG = ox.file.cmd('ffmpeg')
+FFMPEG = None
+for cmd in ('ffmpeg', 'avconv'):
+    cmd = ox.file.cmd(cmd)
+    if subprocess.call(['which', cmd], stdout=subprocess.PIPE) == 0:
+        FFMPEG = cmd
+        break
+if not FFMPEG:
+    print "could not find ffmpeg, make sure its installed and available in PATH"
 FPS = 25
 
 class Video(object):