media_video: reduce default resolution from 720p to 640p

Change-Id: I3d3cf3e11625ef52beedf514e903a997648ce74a
Tuleap: #430

src/media/video/video_device.h

@@ -90,11 +90,14 @@ public:
     }
 
     /* Default setting is found by using following rules:
-     * - frame height <= 720 pixels
+     * - frame height <= 640 pixels
      * - frame rate >= 10 fps
      */
     VideoSettings getDefaultSettings() const {
         auto settings = getSettings();
+        auto channels = getChannelList();
+        if (channels.empty())
+            return {};
         settings.channel = getChannelList().front();
 
         VideoSize max_size {0, 0};
@@ -102,7 +105,7 @@ public:
 
         auto sizes = getSizeList(settings.channel);
         for (auto& s : sizes) {
-            if (s.second > 720)
+            if (s.second > 640)
                 continue;
             auto rates = getRateList(settings.channel, s);
             if (rates.empty())