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

media/video/video_decode_accelerator.h

 // Copyright (c) 2012 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.
 
 #ifndef MEDIA_VIDEO_VIDEO_DECODE_ACCELERATOR_H_
 #define MEDIA_VIDEO_VIDEO_DECODE_ACCELERATOR_H_
 
 #include <memory>
 #include <vector>
 
@@ skipping 16 matching lines @@
   // |max_resolution| and |min_resolution| are inclusive.
   struct MEDIA_EXPORT SupportedProfile {
     SupportedProfile();
     ~SupportedProfile();
     VideoCodecProfile profile;
     gfx::Size max_resolution;
     gfx::Size min_resolution;
   };
   using SupportedProfiles = std::vector<SupportedProfile>;
 
+  struct MEDIA_EXPORT Capabilities {
+    Capabilities();
+    ~Capabilities();
+    // Flags that can be associated with a VDA.
+    enum Flags {
+      NO_FLAGS = 0,
+
+      // If set, then the VDA makes no guarantees that it won't stall before
+      // sending all the picture buffers to the client via PictureReady.
+      CAN_STALL_ANY_TIME = 1 << 0,

[Pawel Osciak, 2015/12/05 00:18:55]

My feeling is that "stall" is a very specific term that a person not familiar
with how our media pipeline works will likely not understand. Actually, I'm
still not sure I understand this fully myself. "Any time" also feels quite
confusing to me, what does it really tell us?

I'd really appreciate a precise explanation here if possible please. For example
(and please correct this if this is wrong, I am not sure if I am understanding
"stall" in this context correctly either):

"A stall happens when a VDA does not return some or all decoded and ready to be
displayed pictures via PictureReady() to the client, even though it is expected
to. In that case... [...explanation show should the client behave then...]"

Thanks.

[liberato (no reviews please), 2015/12/07 19:04:40]

i agree that it is rather specific.  i chose the name to match
CanReadWithoutStalling.  the problem is that it isn't exactly the right word
there, either.  it is more "CanReadWithoutMaybeDeadlocking" -- nobody actually
guarantees that the decoded frames are available immediately, only that they
will become available if one sends enough input and waits long enough.

i've rewritten the comment.

+    };
+
+    SupportedProfiles supported_profiles;
+    Flags flags;
+  };
+
   // 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
   // statistics.
   enum Error {
     // An operation was attempted during an incompatible decoder state.
     ILLEGAL_STATE = 1,
     // Invalid argument was passed to an API method.
     INVALID_ARGUMENT,
     // Encoded input is unreadable.
@@ skipping 149 matching lines @@
 // Specialize std::default_delete so that scoped_ptr<VideoDecodeAccelerator>
 // uses "Destroy()" instead of trying to use the destructor.
 template <>
 struct MEDIA_EXPORT default_delete<media::VideoDecodeAccelerator> {
   void operator()(media::VideoDecodeAccelerator* vda) const;
 };
 
 }  // namespace std
 
 #endif  // MEDIA_VIDEO_VIDEO_DECODE_ACCELERATOR_H_