Motown in-proc streaming framework used to implement media services.

services/media/framework/conversion_pipeline_builder.h

Index: services/media/framework/conversion_pipeline_builder.h
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+// 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_CONVERSION_PIPELINE_BUILDER_H_
+#define SERVICES_MEDIA_FRAMEWORK_CONVERSION_PIPELINE_BUILDER_H_
+
+#include "services/media/framework/engine.h"
+#include "services/media/framework/packet.h"
+#include "services/media/framework/stream_type.h"
+
+namespace mojo {
+namespace media {
+
+// Attempts to add transforms to the given pipeline to convert in_type to a
+// type compatible with out_type_sets. If it succeeds, returns true, updates

[jeffbrown, 2016/02/02 05:35:46]

I feel like there's a parameter missing here to provide a resolver for the type
converters, unless that's hardcoded or something.  Would that state reasonably
be part of the Engine's context?  (Should this method live on Engine?)

[dalesat, 2016/02/02 21:46:38]

Yes, this can be expanded to accommodate more scenarios, including ones in which
the caller adds their own sauce. It would be a cool improvement on the
framework, though I doubt our own needs will motivate that. More likely, we'll
focus on the third-party extensibility that happens when someone adds e.g. a
demux or decoder service. That pipeline building will be happening at the mojo
ipc level, not here in the bowels of service implementation.

I deliberately kept this separate from the engine. The engine has no sense of
media type, and I think this is a good separation of concerns. With this
approach, a completely different pipeline builder can be employed.

+// *output and delivers the resulting output type via *out_type. If it fails,
+// returns false, sets *out_type to nullptr and leaves *output unchanged.
+bool BuildConversionPipeline(
+    const StreamTypePtr& in_type,
+    const StreamTypeSetsPtr& out_type_sets,

[jeffbrown, 2016/02/02 05:35:46]

So this captures one-to-many demux cases but not mux cases.  Does that matter?

[dalesat, 2016/02/02 21:46:38]

That's currently out of scope for this function. It wasn't my intention that
this function do all the graph building. The MediaSource service, for example,
uses this function to convert a stream to a requested type. It understands
demuxes and doesn't need help with those. 

+    Engine* engine,
+    Engine::Output* output,
+    StreamTypePtr* out_type);
+
+}  // namespace media
+}  // namespace mojo
+
+#endif // SERVICES_MEDIA_FRAMEWORK_CONVERSION_PIPELINE_BUILDER_H_