MojoVideoDecoder: Plumb metadata methods.

media/mojo/interfaces/video_decoder.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.
 
 module media.mojom;
 
 import "media/mojo/interfaces/media_types.mojom";
 
 interface VideoDecoder {
   // Initialize the decoder. This must be called before any other method.
   //
   // |decoder_buffer_pipe| will be used to transfer encoded data for each
   // DecoderBuffer.
   //
   // TODO(sandersd): Rename to Initialize() if/when
   // media::VideoDecoder::Initialize() is renamed to Configure().
   Construct(associated VideoDecoderClient client,
             handle<data_pipe_consumer> decoder_buffer_pipe);
 
   // Configure (or reconfigure) the decoder. This must be called before decoding
   // any frames, and must not be called while there are pending Initialize(),
   // Decode(), or Reset() requests.
   //
   // If |low_delay| is true, the decoder must output frames as soon as possible;
   // in particular, it must not wait for another Decode() request, except as
-  // required for frame reordering.
-  Initialize(VideoDecoderConfig config, bool low_delay) => (bool success);
+  // required for frame reordering. Implementations must fail initialization if
+  // they cannot satisfy this requirement.
+  //
+  // On completion, the callback also includes |needs_bitstream_conversion|,
+  // indicating whether decode buffers need bitstream conversion, and
+  // |max_decode_requests|, the maximum number of concurrent Decode() requests
+  // the implementation supports.
+  Initialize(VideoDecoderConfig config, bool low_delay) =>
+      (bool success, bool needs_bitstream_conversion,
+       int32 max_decode_requests);
 
   // Request decoding of exactly one frame or an EOS buffer. This must not be
-  // called while there are pending Configure(), Reset(), or Decode() requests.
+  // called while there are pending Initialize(), Reset(), or Decode(EOS)
+  // requests.
   //
   // Implementations must eventually execute the callback, even if Decode() is
   // not called again. It is not required that the decode status match the
-  // actual result of decoding a frame; only that decode errors are eventually
-  // reported (such as at EOS). The purpose of the callback is primarily for
-  // Decode() rate control.
+  // actual result of decoding the buffer, only that decode errors are
+  // eventually reported (such as at EOS).
   //
-  // If |buffer| is an EOS buffer, implementations execute all other pending
-  // Decode() callbacks and output all pending frames before executing the EOS
-  // buffer Decode() callback. (That is, they must flush.)
-  //
-  // TODO(sandersd): Plumb GetMaxDecodeRequests() so that parallel Decode()
-  // requests can be allowed.
+  // If |buffer| is an EOS buffer, implementations must execute all other
+  // pending Decode() callbacks and output all pending frames before executing
+  // the Decode(EOS) callback. (That is, they must flush.)
   Decode(DecoderBuffer buffer) => (DecodeStatus status);
 
   // Reset the decoder. All ongoing Decode() requests must be completed or
   // aborted before executing the callback. This must not be called while there
   // is a pending Initialize() request.
   Reset() => ();
 };
 
 interface VideoDecoderClient {
   // Output a decoded frame. Frames must be output in presentation order.
   OnVideoFrameDecoded(VideoFrame frame);
 };