media: Support transporting 0-byte DecoderBuffer over mojo

media/mojo/interfaces/media_types.mojom

 // Copyright 2014 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 "ui/gfx/geometry/mojo/geometry.mojom";
 import "mojo/common/common_custom_types.mojom";
 
 // See media/base/buffering_state.h for descriptions.
@@ skipping 86 matching lines @@
   string key_id;
   string iv;
   array<SubsampleEntry> subsamples;
 };
 
 // This defines a mojo transport format for media::DecoderBuffer.
 struct DecoderBuffer {
   mojo.common.mojom.TimeDelta timestamp;
   mojo.common.mojom.TimeDelta duration;
 
-  // The number of bytes present in this buffer.  The data is not serialized
+  // Whether the buffer is an end-of-stream (EOS) buffer.
+  bool is_end_of_stream;

[alokp, 2016/11/08 21:34:08]

If "data_size == 0 && side_data_size == 0", would it be correct to conclude that
this is eos buffer?

[xhwang, 2016/11/08 22:13:51]

We could, but I feel it's really hacky and confusing. A dedicated flag here
seems more clear to me.

[alokp, 2016/11/08 22:17:30]

I agree. Should we add this flag to media::DecoderBuffer as well to keep things
consistent? "data_ == NULL" is equally hacky.

[xhwang, 2016/11/08 22:28:35]

Agreed. I tried refactor DecoderBuffer last week but it's more involved than
what I thought. This code is pretty old and needs some non-trivial work.

I added a comment in the bug:
https://bugs.chromium.org/p/chromium/issues/detail?id=663438#c2

+
+  // The number of bytes present in this buffer. The data is not serialized
   // along with this structure and must be read from a separate DataPipe.
+  // Note that |data_size| could be zero even for a non-EOS buffer (e.g.
+  // with non-empty |size_data|). See http://crbug.com/663438
   uint32 data_size;
 
   // Indicates whether or not this buffer is a random access point.
   bool is_key_frame;
 
   // Empty when |side_data| doesn't exist.
   array<uint8> side_data;
 
   // DecryptConfig for a encrypted buffer. NULL if the buffer is not encrypted.
   DecryptConfig? decrypt_config;
@@ skipping 68 matching lines @@
 };
 
 struct PipelineStatistics {
   uint64 audio_bytes_decoded;
   uint64 video_bytes_decoded;
   uint32 video_frames_decoded;
   uint32 video_frames_dropped;
   int64 audio_memory_usage;
   int64 video_memory_usage;
 };