Don't require VDAs to return all PictureBuffers at once.

media/video/video_decode_accelerator.h

Index: media/video/video_decode_accelerator.h
diff --git a/media/video/video_decode_accelerator.h b/media/video/video_decode_accelerator.h
index da184ee2d46247169282e08793638e64aa18cc81..5ab81c364d8374e702c6cb16a696a5c9fa1966fe 100644
--- a/media/video/video_decode_accelerator.h
+++ b/media/video/video_decode_accelerator.h
@@ -34,6 +34,29 @@ class MEDIA_EXPORT VideoDecodeAccelerator {
   };
   using SupportedProfiles = std::vector<SupportedProfile>;
 
+  struct MEDIA_EXPORT Capabilities {
+    Capabilities();
+    ~Capabilities();
+    // Flags that can be associated with a VDA.
+    enum Flags {
+      NO_FLAGS = 0,
+
+      // Normally, the VDA is required to be able to provide all PictureBuffers
+      // to the client via PictureReady(), even if the client does not return
+      // any of them via ReusePictureBuffer().  The client is only required to
+      // return PictureBuffers when it holds all of them, if it wants to get
+      // more decoded output.  See VideoDecoder::CanReadWithoutStalling for
+      // more context.
+      // If this flag is set, then the VDA does not make this guarantee.  The
+      // client must return PictureBuffers to be sure that new frames will be
+      // provided via PictureReady.

[Pawel Osciak, 2015/12/09 01:31:49]

Nice! Really clear. Thank you.

[liberato (no reviews please), 2015/12/09 22:15:31]

Acknowledged.

+      CAN_STALL_ANY_TIME = 1 << 0,

[Pawel Osciak, 2015/12/09 01:31:49]

Might I suggest NEEDS_ALL_PICTURE_BUFFERS_TO_DECODE for the name though (please
see my comment in gpu_video_decoder.h).

[liberato (no reviews please), 2015/12/09 22:15:31]

Done.

+    };
+
+    SupportedProfiles supported_profiles;
+    Flags flags;

[Pawel Osciak, 2015/12/09 01:31:49]

Ah now I see why the cast was needed, somehow missed this. This member shouldn't
be an enum, because enum variables can only have one value, while we intend to
use "flags" as a bit field. This should be an uint32.

[liberato (no reviews please), 2015/12/09 22:15:31]

done, and kept the enum to hold the symbolic names of the bits.

+  };
+
   // Enumeration of potential errors generated by the API.
   // Note: Keep these in sync with PP_VideoDecodeError_Dev. Also do not
   // rearrange, reuse or remove values as they are used for gathering UMA