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

media/gpu/v4l2_video_decode_accelerator.cc

Index: media/gpu/v4l2_video_decode_accelerator.cc
diff --git a/media/gpu/v4l2_video_decode_accelerator.cc b/media/gpu/v4l2_video_decode_accelerator.cc
index 01e650a2f3cf35fdb5581f672b957672d9a2ae06..1ec3f5740db5586a16bc049b35c41bfa4527d4ff 100644
--- a/media/gpu/v4l2_video_decode_accelerator.cc
+++ b/media/gpu/v4l2_video_decode_accelerator.cc
@@ -2038,9 +2038,22 @@ uint32_t V4L2VideoDecodeAccelerator::FindImageProcessorInputFormat() {
 }
 
 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;