Video capture: Refactor GetBestMatchedFormat from Win to OS independent

media/video/capture/video_capture_device.cc

Index: media/video/capture/video_capture_device.cc
diff --git a/media/video/capture/video_capture_device.cc b/media/video/capture/video_capture_device.cc
index 3b74417cbf823c0e9d235953809fb40a2cadaaef..69d7d1af1eb9b395f9f112ce25028bcc06a7b92b 100644
--- a/media/video/capture/video_capture_device.cc
+++ b/media/video/capture/video_capture_device.cc
@@ -4,6 +4,8 @@
 
 #include "media/video/capture/video_capture_device.h"
 
+#include <cmath>
+
 #include "base/i18n/timezone.h"
 #include "base/strings/string_util.h"
 
@@ -85,4 +87,33 @@ bool VideoCaptureDevice::InitializeImageCapture(
   return false;
 }
 
+uint64_t DiffVideoCaptureFormat(const VideoCaptureFormat& requested,
+                                const VideoCaptureFormat& supported) {
+  const uint64_t diff_width =
+      std::abs(requested.frame_size.width() - supported.frame_size.width());
+  const uint64_t diff_height =
+      std::abs(requested.frame_size.height() - supported.frame_size.height());
+  // We need to distinguish between rational frame rates (e.g. 29.97 and 30.0).
+  // Therefore, multiply with a large constant before converting to int.
+  const uint64_t diff_frame_rate = static_cast<uint64_t>(
+      kFrameRatePrecision *
+      std::fabs(requested.frame_rate - supported.frame_rate));
+  const uint64_t diff_color_format = supported.pixel_format;

[perkj_chrome, 2014/10/10 09:17:13]

I am afraid that pixelformat is not really sorted in the order of preference.
Can we move YV12 to just below I420 and document in that list that it s sorted.

[magjed_chromium, 2014/10/10 11:21:26]

Done.

+
+  const int resolution_bit_size = 16;

[perkj_chrome, 2014/10/10 09:17:13]

nit:
http://google-styleguide.googlecode.com/svn/trunk/cppguide.html#Constant_Names

[magjed_chromium, 2014/10/10 11:21:25]

These constants are in local scope, so it's ok to use the usual variable naming:
"This convention may optionally be used for compile-time constants of local
scope; otherwise the usual variable naming rules apply."

+  const int frame_rate_bit_size = 24;
+  const int color_format_bit_size = 8;
+
+  DCHECK(diff_width < (1 << resolution_bit_size));
+  DCHECK(diff_height < (1 << resolution_bit_size));
+  DCHECK(diff_frame_rate < (1 << frame_rate_bit_size));
+  DCHECK(diff_color_format < (1 << color_format_bit_size));
+
+  uint64_t distance = diff_height;
+  distance = diff_width | (distance << resolution_bit_size);
+  distance = diff_frame_rate | (distance << frame_rate_bit_size);
+  distance = diff_color_format | (distance << color_format_bit_size);
+  return distance;
+}
+
 }  // namespace media