return comparevideos stdout and fix missing device case

webrtc/tools/video_analysis.py

 #!/usr/bin/env python
 # Copyright (c) 2017 The WebRTC project authors. All Rights Reserved.
 #
 # Use of this source code is governed by a BSD-style license
 # that can be found in the LICENSE file in the root of the source
 # tree. An additional intellectual property rights grant can be found
 # in the file PATENTS.  All contributing project authors may
 # be found in the AUTHORS file in the root of the source tree.
 
 import glob
@@ skipping 166 matching lines @@
   # usb device port mappings and it's the same in all usbN folders. Tested
   # on Ubuntu 14.04.
   v4l_device_path = '/sys/bus/usb/devices/usb1/1-1/driver/**/**/video4linux/'
   v4l_ref_device = glob.glob('%s%s' % (v4l_device_path, ref_video_device))
   v4l_test_device = glob.glob('%s%s' % (v4l_device_path, test_video_device))
   usb_ports = []
   paths = []
 
   # Split on the driver folder first since we are only interested in the
   # folders thereafter.
-  ref_path = str(v4l_ref_device).split('driver')[1].split('/')
-  test_path = str(v4l_test_device).split('driver')[1].split('/')
-  paths.append(ref_path)
-  paths.append(test_path)
+  try:
+    ref_path = str(v4l_ref_device).split('driver')[1].split('/')
+    test_path = str(v4l_test_device).split('driver')[1].split('/')
+  except IndexError:
+    print 'Could not find one or both of the specified recording devices.'
+  else:
+    paths.append(ref_path)
+    paths.append(test_path)
 
-  for path in paths:
-    for usb_id in path:
-      # Look for : separator and then use the first element in the list.
-      # E.g 3-3.1:1.0 split on : and [0] becomes 3-3.1 which can be used
-      # for bind/unbind.
-      if ':' in usb_id:
-        usb_ports.append(usb_id.split(':')[0])
+    for path in paths:
+      for usb_id in path:
+        # Look for : separator and then use the first element in the list.
+        # E.g 3-3.1:1.0 split on : and [0] becomes 3-3.1 which can be used
+        # for bind/unbind.
+        if ':' in usb_id:
+          usb_ports.append(usb_id.split(':')[0])
+
   return usb_ports
 
 
 def RestartMagewellDevices(ref_video_device_path, test_video_device_path):
   """Reset the USB ports where Magewell capture devices are connected to.
 
   Performs a soft reset by using USB unbind and bind.
   This is due to Magewell capture devices have proven to be unstable after the
   first recording attempt.
 
@@ skipping 232 matching lines @@
     '--ffmpeg_path', options.ffmpeg,
     '--stats_file_ref', os.path.join(os.path.dirname(cropped_ref_file),
         cropped_ref_file + '_stats.txt'),
     '--stats_file_test', os.path.join(os.path.dirname(cropped_test_file),
         cropped_test_file + '_stats.txt'),
     '--yuv_frame_height', crop_height,
     '--yuv_frame_width', crop_width
   ]
 
   with open(result_file_name, 'w') as f:
-    compare_video_recordings = subprocess.Popen(compare_cmd, stdout=f)
-    compare_video_recordings.wait()
-  if compare_video_recordings.returncode != 0:
-    raise CompareVideosError('Failed to perform comparison.')
-  else:
-    print 'Result recorded to: ' + os.path.abspath(result_file_name)
-    print 'Comparison done!'
+    try:
+      compare_video_recordings = subprocess.check_output(compare_cmd)
+      f.write(compare_video_recordings)
+    except subprocess.CalledProcessError as error:
+      raise CompareVideosError('Failed to perform comparison: %s' % error)
+    else:
+      print 'Result recorded to: %s' % os.path.abspath(result_file_name)
+      print 'Comparison done!'
+      return compare_video_recordings
 
 
 def main():
   """The main function.
 
   A simple invocation is:
   ./run_video_analysis.py \
     --app_name AppRTCMobile \
     --ffmpeg ./ffmpeg --ref_video_device=/dev/video0 \
     --test_video_device=/dev/video1 \
@@ skipping 26 matching lines @@
   if options.compare_videos_script:
     CompareVideos(options, recording_result['cropped_ref_file'],
                   recording_result['cropped_test_file'])
   else:
     print ('Skipping compare videos step due to compare_videos flag were not '
            'passed.')
 
 
 if __name__ == '__main__':
   sys.exit(main())