Use explicit flush for ArcVideoAccelerator.

components/arc/common/video_accelerator.mojom

 // Copyright 2016 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.
 
 // This file defined the mojo interface between Android and Chromium for video
 // decoding and encoding. See comments of ArcVideoAccelerator for more info.
 
 module arc.mojom;
 
 [Extensible]
 enum HalPixelFormatExtension {
   HAL_PIXEL_FORMAT_YCbCr_420_888 = 0x23,
   HAL_PIXEL_FORMAT_H264 = 0x34363248,
   HAL_PIXEL_FORMAT_VP8 = 0x00385056,
 };
 
 enum PortType {
   PORT_INPUT = 0,
   PORT_OUTPUT = 1,
 };
 
-[Extensible]
-enum BufferFlag {
-  BUFFER_FLAG_EOS = 1,
-};
-
 struct BufferMetadata {
   int64 timestamp;  // in microseconds
   uint32 flags;
   uint32 bytes_used;
 };
 
 struct VideoFormat {
   uint32 pixel_format;
   uint32 buffer_size;
 
@@ skipping 24 matching lines @@
   BindSharedMemory@1(PortType port, uint32 index, handle ashmem_fd,
                    uint32 offset, uint32 length);
 
   BindDmabuf@2(PortType port, uint32 index, handle dmabuf_fd);
 
   UseBuffer@3(PortType port, uint32 index, BufferMetadata metadata);
 
   SetNumberOfOutputBuffers@4(uint32 number);
 
   Reset@5();
+
+  Flush@6();

[dcheng, 2016/05/07 06:18:11]

Out of curiosity, how come we don't do something like Flush@6() => (), so the
caller can just wait for the return callback?

[Owen Lin, 2016/05/09 07:04:41]

Just make it similar to the VDA interface:

https://code.google.com/p/chromium/codesearch#chromium/src/media/video/video_...

[dcheng, 2016/05/09 21:22:00]

Wouldn't the code be simpler though if we just used the appropriate mojo
primitives? Is there some advantage to having two separate interfaces for one
logical call that I'm missing?

[Owen Lin, 2016/05/10 08:26:33]

I think you're right that we can use mojo primitives for Flush() -->
onFlushDone() or Reset()--> onResetDone().

But I don't see much benefits/difference. We still need the interface for error
handling and other callbacks. Adding these completion callbacks to the interface
seems a better idea. Otherwise, in Chromium side, we need to keep those
callbacks and invoke them when we are notified by
VDA::Client::Notify(Flush|Reset)Done().

In addition, that also makes people who are familiar with VDA easy to
match/understand the code.

The question makes me to think why VDA was not designed as using
Flush(base::Closure callback). But I don't see strong reason/benefit to change
it.

 };
 
 interface VideoAcceleratorServiceClient {
   enum Error {
     NO_ERROR = 0,
     ILLEGAL_STATE = 1,
     INVALID_ARGUMENT = 2,
     UNREADABLE_INPUT = 3,
     PLATFORM_FAILURE = 4,
   };
 
   Init@0(VideoAcceleratorService service_ptr);
 
   OnError@1(Error error);
 
   OnBufferDone@2(PortType port, uint32 index, BufferMetadata metadata);
 
   OnResetDone@3();
 
   OnOutputFormatChanged@4(VideoFormat format);
+
+  OnFlushDone@5();
 };