chromeos: decode video into NV12 format instead of RGBA in vaapi decoder

cc/resources/video_resource_updater.cc

Index: cc/resources/video_resource_updater.cc
diff --git a/cc/resources/video_resource_updater.cc b/cc/resources/video_resource_updater.cc
index 9e697580d3f22d696c93e556f9afb19c9ba23e16..2fdfbc10694cb4b058fbd326d8df66e10b8fd199 100644
--- a/cc/resources/video_resource_updater.cc
+++ b/cc/resources/video_resource_updater.cc
@@ -63,8 +63,12 @@ VideoFrameExternalResources::ResourceType ResourceTypeForVideoFrame(
     case media::PIXEL_FORMAT_NV12:
       switch (video_frame->mailbox_holder(0).texture_target) {
         case GL_TEXTURE_EXTERNAL_OES:
-        case GL_TEXTURE_2D:
-          return VideoFrameExternalResources::YUV_RESOURCE;
+        case GL_TEXTURE_2D: {
+          bool is_dual_gmb = video_frame->mailbox_holder(1).texture_target ==

[gurchetansingh, 2017/06/22 23:31:59]

What is a "dual gmb", one that as more than plane or more than one kernel buffer
backing it?

[dshwang, 2017/06/23 01:07:05]

According to NV12_DUAL_GMB comment, it consists of One R8 and one RG88 GMB
https://cs.chromium.org/chromium/src/media/renderers/gpu_video_accelerator_fa...

It's used by GpuMemoryBufferVideoFramePool in the case the platform cannot
support real native NV12 GBM.

[gurchetansingh, 2017/06/23 03:18:33]

Why is a VideoFrameExternalResources::YUV_RESOURCE returned when  a is_dual_gmb
== true?

[dshwang, 2017/06/23 23:25:14]

YUV_RESOURCE creates YUVVideoDrawQuad, whose shader lookup y, u, v texture
separately. Of course, it never be overlay candidate.

RGB_RESOURCE creates TextureDrawQuad, whose shader lookup just rgba texture,
because EGL_EXT_image_dma_buf_import convert YUV to RGBA under the hood.
https://www.khronos.org/registry/EGL/extensions/EXT/EGL_EXT_image_dma_buf_imp...

[gurchetansingh, 2017/06/24 01:50:48]

How does whether it's a YUVVideoDrawQuad or a TextureDrawQuad affect the shaders
and EGL import?  Can you point me to the shader code?

[Daniele Castagna, 2017/06/26 18:06:43]

The EGL import is done earlier by the video decoder. This code just gets a
VideoFrame with one or more mailboxes then creates the resource (a cc concept)
and then VideoLayerImpl::AppendQuads create the quad based on the resource type.

The shader is generated, you probably want to look at
FragmentShader::GetShaderSource()  in cc/output/shader.cc
Take a look at INPUT_COLOR_SOURCE_YUV_TEXTURES for the yuv bits.

+                             video_frame->mailbox_holder(0).texture_target;
+          return is_dual_gmb ? VideoFrameExternalResources::YUV_RESOURCE

[Daniele Castagna, 2017/06/26 18:06:43]

What if a VideoFrame is YUV with 3 textures? Shouldn't we still return a
YUV_RESOURCE here?

[dshwang, 2017/06/28 02:08:34]

yes, YUV_RESOURCE can handle both y & uv planes and y & u & v planes.
PIXEL_FORMAT_NV12 never has 3 textures tho.

+                             : VideoFrameExternalResources::RGB_RESOURCE;
+        }
         case GL_TEXTURE_RECTANGLE_ARB:
           return VideoFrameExternalResources::RGB_RESOURCE;
         default: