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;
   V4L2ImageProcessor image_processor(image_processor_device_);
   std::vector<uint32_t> processor_output_formats =
       image_processor.GetSupportedOutputFormats();

[kcwu, 2016/08/19 05:50:59]

I'm wondering what if we simply push_front preferred format to
processor_output_formats.

Or move preferred format to the front. For example,
(psuedo code)
it = find(...);
if (it != end) {
  swap(it, begin);
}

[wuchengli, 2016/08/19 06:01:42]

Done. Good idea.

+
+  // Check the preferred format first.
+  if (device_->CanCreateEGLImageFrom(kPreferredEGLImageFormat)) {
+    std::vector<uint32_t>::iterator it =
+        std::find(processor_output_formats.begin(),
+                  processor_output_formats.end(), kPreferredEGLImageFormat);
+    if (it != processor_output_formats.end()) {

[kcwu, 2016/08/19 05:50:59]

swap these two if-conditions at line 2051 and 2047.
It doesn't make sense to query device first and then found the format are not
what we want.

[wuchengli, 2016/08/19 06:01:42]

The code is removed.

+      DVLOGF(1) << "Image processor output format=" << kPreferredEGLImageFormat;
+      return kPreferredEGLImageFormat;
+    }
+  }
+
   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