Motown: Remove LPCM optimizations, fix prepare, add flush, add ActiveMultistreamSink model/stage

services/media/framework/stages/multistream_source_stage.h

Index: services/media/framework/stages/multistream_source_stage.h
diff --git a/services/media/framework/stages/multistream_source_stage.h b/services/media/framework/stages/multistream_source_stage.h
new file mode 100644
index 0000000000000000000000000000000000000000..a6f488b52855303f7496b948edb323bf12b79831
--- /dev/null
+++ b/services/media/framework/stages/multistream_source_stage.h
@@ -0,0 +1,60 @@
+// 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.
+
+#ifndef SERVICES_MEDIA_FRAMEWORK_STAGES_MULTISTREAM_SOURCE_STAGE_H_
+#define SERVICES_MEDIA_FRAMEWORK_STAGES_MULTISTREAM_SOURCE_STAGE_H_
+
+#include <vector>
+
+#include "services/media/framework/models/multistream_source.h"
+#include "services/media/framework/stages/stage.h"
+
+namespace mojo {
+namespace media {
+
+// A stage that hosts a MultistreamSource.
+class MultistreamSourceStage : public Stage {
+ public:
+  MultistreamSourceStage(std::shared_ptr<MultistreamSource> source);
+
+  ~MultistreamSourceStage() override;
+
+  // Stage implementation.
+  size_t input_count() const override;
+
+  Input& input(size_t index) override;
+
+  size_t output_count() const override;
+
+  Output& output(size_t index) override;
+
+  PayloadAllocator* PrepareInput(size_t index) override;
+
+  void PrepareOutput(
+      size_t index,
+      PayloadAllocator* allocator,
+      const PrepareCallback& callback) override;
+
+  void UnprepareOutput(size_t index) override;
+
+  void Update(Engine* engine) override;
+
+  void FlushInput(
+      size_t index,
+      const FlushCallback& callback) override;
+
+  void FlushOutput(size_t index) override;
+
+ private:
+  std::vector<Output> outputs_;

[johngro, 2016/02/08 22:33:37]

Why the asymmetry between the MultistreameSink and the MultistreamSource here? 
IOW - it seems like inputs can be dynamically be added and removed from
MultistreamSinks, but not from sources.

[dalesat, 2016/02/09 00:34:11]

So far, there's no need to dynamically add outputs to a source. Splitters will
need to add outputs, but they aren't sources.

[johngro, 2016/02/09 21:00:36]

What about a demux?  For example, what about an MPEG2-TS demux which needs to
process the stream and parse the PAT/PMTs before knowing the available programs
and substream construction of the programs before it can generate its outputs?

Likewise, what about an MP4 or Matroska container?  The demux code is going to
need to be connected to the transport and chew on the data for a while before it
has any idea what the contents of the container are.

If you want to leave this like it is for now and address it in a subsequent CL,
that's fine, but I think that there are real world examples of where this is
going to be needed.

If you are going to leave this as is, at least please add a comment or file a
work item in the bug tracker indicating that this needs to be done someday.

[dalesat, 2016/02/10 21:37:24]

I agree this may be needed in the future. I'm not inclined to add this
capability until we can actually use it and prove that we've adequately
addressed the need.

Adding a comment.

+  std::shared_ptr<MultistreamSource> source_;
+  PacketPtr cached_packet_;
+  size_t cached_packet_output_index_;
+  size_t ended_streams_;
+};
+
+}  // namespace media
+}  // namespace mojo
+
+#endif  // SERVICES_MEDIA_FRAMEWORK_STAGES_MULTISTREAM_SOURCE_STAGE_H_