V4L2VDA: use YV12 as output format if processor supports it.

media/gpu/v4l2_video_decode_accelerator.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "media/gpu/v4l2_video_decode_accelerator.h"
 
 #include <dlfcn.h>
 #include <errno.h>
 #include <fcntl.h>
 #include <linux/videodev2.h>
@@ skipping 2020 matching lines @@
                   fmtdesc.pixelformat) != processor_input_formats.end()) {
       DVLOGF(1) << "Image processor input format=" << fmtdesc.pixelformat;
       return fmtdesc.pixelformat;
     }
     ++fmtdesc.index;
   }
   return 0;
 }
 
 uint32_t V4L2VideoDecodeAccelerator::FindImageProcessorOutputFormat() {
+  const uint32_t kPreferredEGLImageFormat = V4L2_PIX_FMT_YVU420;

[kcwu, 2016/08/19 06:27:33]

could you add comment here or in commit log, why this format is preferred?

[wuchengli, 2016/08/21 08:14:42]

Done.

   V4L2ImageProcessor image_processor(image_processor_device_);
   std::vector<uint32_t> processor_output_formats =
       image_processor.GetSupportedOutputFormats();
+
+  // Move the preferred format to the front.
+  std::vector<uint32_t>::iterator it =

[kcwu, 2016/08/19 06:27:33]

how about use "auto" type?

[wuchengli, 2016/08/21 08:14:42]

Done.

+      std::find(processor_output_formats.begin(),
+                processor_output_formats.end(), kPreferredEGLImageFormat);
+  if (it != processor_output_formats.end())
+    std::iter_swap(it, processor_output_formats.begin());
+
   for (uint32_t processor_output_format : processor_output_formats) {
     if (device_->CanCreateEGLImageFrom(processor_output_format)) {
       DVLOGF(1) << "Image processor output format=" << processor_output_format;
       return processor_output_format;
     }
   }
 
   return 0;
 }
 
@@ skipping 217 matching lines @@
       Enqueue();
   }
 }
 
 void V4L2VideoDecodeAccelerator::ImageProcessorError() {
   LOGF(ERROR) << "Image processor error";
   NOTIFY_ERROR(PLATFORM_FAILURE);
 }
 
 }  // namespace media