chromium/media/base/pipeline_impl.h

// Copyright 2016 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef MEDIA_BASE_PIPELINE_IMPL_H_
#define MEDIA_BASE_PIPELINE_IMPL_H_

#include <memory>
#include <optional>

#include "base/memory/raw_ptr.h"
#include "base/memory/scoped_refptr.h"
#include "base/memory/weak_ptr.h"
#include "base/task/sequenced_task_runner.h"
#include "base/threading/thread_checker.h"
#include "base/time/time.h"
#include "media/base/media_export.h"
#include "media/base/pipeline.h"
#include "media/base/renderer.h"
#include "media/base/renderer_factory_selector.h"

namespace base {
class SingleThreadTaskRunner;
}

namespace media {

class MediaLog;

// Callbacks used for Renderer creation. When the RendererType is nullopt, the
// current base one will be created.
CreateRendererCB;
RendererCreatedCB;
AsyncCreateRendererCB;

// Pipeline runs the media pipeline.  Filters are created and called on the
// task runner injected into this object. Pipeline works like a state
// machine to perform asynchronous initialization, pausing, seeking and playing.
//
// Here's a state diagram that describes the lifetime of this object.
//
//   [ *Created ]                       [ Any State ]
//         | Start()                         | Stop()
//         V                                 V
//   [ Starting ]                       [ Stopping ]
//         |                                 |
//         V                                 V
//   [ Playing ] <---------.            [ Stopped ]
//     |  |  | Seek()      |
//     |  |  V             |
//     |  | [ Seeking ] ---'
//     |  |                ^
//     |  | *TrackChange() |
//     |  V                |
//     | [ Switching ] ----'
//     |                   ^
//     | Suspend()         |
//     V                   |
//   [ Suspending ]        |
//     |                   |
//     V                   |
//   [ Suspended ]         |
//     | Resume()          |
//     V                   |
//   [ Resuming ] ---------'
//
// Initialization is a series of state transitions from "Created" through each
// filter initialization state.  When all filter initialization states have
// completed, we simulate a Seek() to the beginning of the media to give filters
// a chance to preroll. From then on the normal Seek() transitions are carried
// out and we start playing the media.
//
// If Stop() is ever called, this object will transition to "Stopped" state.
// Pipeline::Stop() is never called from within PipelineImpl. It's |client_|'s
// responsibility to call stop when appropriate.
//
// TODO(sandersd): It should be possible to pass through Suspended when going
// from InitDemuxer to InitRenderer, thereby eliminating the Resuming state.
// Some annoying differences between the two paths need to be removed first.
class MEDIA_EXPORT PipelineImpl : public Pipeline { … };

}  // namespace media

#endif  // MEDIA_BASE_PIPELINE_IMPL_H_