diff --git a/removeads.py b/removeads.py
index 956e434..88034be 100755
--- a/removeads.py
+++ b/removeads.py
@@ -237,7 +237,18 @@ def ffmpegConvert(inputFile, inputFormat, outputFile, outputFormat, duration):
         status = ffmpeg.wait()
         if status != 0:
             logger.error('Conversion failed with status code: %d' % status)
-        
+
+def getTSFrame(frame):
+    if 'pts_time' in frame:
+        pts_time = float(frame['pts_time'])
+    elif 'pkt_pts_time' in frame:
+        pts_time = float(frame['pkt_pts_time'])
+    else:
+        logger.error('Impossible to find timestamp of frame %s' % frame)
+        return None
+
+    ts = timedelta(seconds=pts_time)
+    return ts
 
 def getFramesInStream(inputFile, begin, end, streamKind, subStreamId=0):
     logger = logging.getLogger(__name__)
@@ -255,15 +266,9 @@ def getFramesInStream(inputFile, begin, end, streamKind, subStreamId=0):
         if 'frames' in frames:
             frames = frames['frames']
             for frame in frames:
-                if 'pts_time' in frame:
-                    pts_time = float(frame['pts_time'])
-                elif 'pkt_pts_time' in frame:
-                    pts_time = float(frame['pkt_pts_time'])
-                else:
-                    logger.error('Impossible to find timestamp of frame %s' % frame)
+                ts = getTSFrame(frame)
+                if ts == None
                     return None
-                
-                ts = timedelta(seconds=pts_time)
                 if begin <= ts and ts <= end:
                     res.append(frame)
             return res
@@ -295,11 +300,15 @@ def getNearestIFrame(inputFile, timestamp, before=True, delta=timedelta(seconds=
             iframes.append(frame)
     
     found = False
-    for frame in iframes: 
-        if before and timedelta(seconds=float(frame['pts_time'])) <= timestamp:
+    for frame in iframes:
+        ts = getTSFrame(frame)
+        if ts == None
+            return None
+      
+        if before and ts <= timestamp:
             found = True
             iframe = frame
-        if not before and timedelta(seconds=float(frame['pts_time'])) >= timestamp:
+        if not before and ts >= timestamp:
             found = True
             iframe = frame
             break
@@ -308,10 +317,16 @@ def getNearestIFrame(inputFile, timestamp, before=True, delta=timedelta(seconds=
         logger.info("Found i-frame at: %s" % iframe)
         logger.debug("Found i-frame at %s" % iframe)
         
-        its = timedelta(seconds=float(iframe['pts_time'])) 
+        its = getTSFrame(iframe)
+        if its == None:
+            return None
+        
         nbFrames = 0
         for frame in frames:
-            ts = timedelta(seconds=float(frame['pts_time'])) 
+            ts = getTSFrame(frame)
+            if ts == None
+                return None
+
             if before:
                 if its <= ts and ts <= timestamp:
                     logger.info("Retrieve a frame between %s and %s at %s" % (its, timestamp, ts))