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;

[mcasas, 2014/10/13 08:18:45]

s/diff_color_format/diff_pixel_format/g

Forgot to subtract from |requested.pixel_format|?

+
+  const int resolution_bit_size = 16;

[mcasas, 2014/10/13 08:18:45]

s/resolution_bit_size/kResolutionBitSize/

this also applies to l.104-105, but read first l.112 .

+  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;

[mcasas, 2014/10/13 08:18:45]

From this point on, this seems to be an obscure linear
combination. I don't think the optimization of using 
<< and | is worth it. Besides, you are taken for 
granted Little Endian, right? Propose:

return diff_height * kHeightWeight + 
    diff_width * kWidthWeight +
    diff_frame_rate * kFrameRateWeight +
    diff_pixel_format * kPixelFormatWeight;

+  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