src/cobalt/media/base/video_renderer_sink.h

// Copyright 2015 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 COBALT_MEDIA_BASE_VIDEO_RENDERER_SINK_H_
#define COBALT_MEDIA_BASE_VIDEO_RENDERER_SINK_H_

#include "base/logging.h"
#include "base/memory/ref_counted.h"
#include "base/time.h"
#include "cobalt/media/base/media_export.h"
#include "cobalt/media/base/video_frame.h"

namespace cobalt {
namespace media {

// VideoRendererSink is an interface representing the end-point for rendered
// video frames.  An implementation is expected to periodically call Render() on
// a callback object.
class MEDIA_EXPORT VideoRendererSink {
 public:
  class RenderCallback {
   public:
    // Returns a VideoFrame for rendering which should be displayed within the
    // presentation interval [|deadline_min|, |deadline_max|].  Returns NULL if
    // no frame or no new frame (since the last Render() call) is available for
    // rendering within the requested interval.  Intervals are expected to be
    // regular, contiguous, and monotonically increasing.  Irregular intervals
    // may affect the rendering decisions made by the underlying callback.
    //
    // If |background_rendering| is true, the VideoRenderSink is pumping
    // callbacks at a lower frequency than normal and the results of the
    // Render() call may not be used.
    virtual scoped_refptr<VideoFrame> Render(base::TimeTicks deadline_min,
                                             base::TimeTicks deadline_max,
                                             bool background_rendering) = 0;

    // Called by the sink when a VideoFrame previously returned via Render() was
    // not actually rendered.  Must be called before the next Render() call.
    virtual void OnFrameDropped() = 0;

    virtual ~RenderCallback() {}
  };

  // Starts video rendering.  See RenderCallback for more details.  Must be
  // called to receive Render() callbacks.  Callbacks may start immediately, so
  // |callback| must be ready to receive callbacks before calling Start().
  virtual void Start(RenderCallback* callback) = 0;

  // Stops video rendering, waits for any outstanding calls to the |callback|
  // given to Start() to complete before returning.  No new calls to |callback|
  // will be issued after this method returns.  May be used as a means of power
  // conservation by the sink implementation, so clients should call this
  // liberally if no new frames are expected.
  virtual void Stop() = 0;

  // Instead of using a callback driven rendering path, allow clients to paint a
  // single frame as they see fit without regard for the compositor; this is
  // useful for painting poster images or hole frames without having to issue a
  // Start() -> Render() -> Stop(). Clients are free to mix usage of Render()
  // based painting and PaintSingleFrame().
  virtual void PaintSingleFrame(const scoped_refptr<VideoFrame>& frame,
                                bool repaint_duplicate_frame = false) = 0;

  virtual ~VideoRendererSink() {}
};

}  // namespace media
}  // namespace cobalt

#endif  // COBALT_MEDIA_BASE_VIDEO_RENDERER_SINK_H_