src/media/base/buffers.h

// Copyright (c) 2012 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.

// Defines a base class for representing timestamped media data. Every buffer
// contains a timestamp in microseconds describing the relative position of
// the buffer within the media stream, and the duration in microseconds for
// the length of time the buffer will be rendered.
//
// Timestamps are derived directly from the encoded media file and are commonly
// known as the presentation timestamp (PTS).  Durations are a best-guess and
// are usually derived from the sample/frame rate of the media file.
//
// Due to encoding and transmission errors, it is not guaranteed that timestamps
// arrive in a monotonically increasing order nor that the next timestamp will
// be equal to the previous timestamp plus the duration.
//
// In the ideal scenario for a 25fps movie, buffers are timestamped as followed:
//
//               Buffer0      Buffer1      Buffer2      ...      BufferN
// Timestamp:        0us      40000us      80000us      ...   (N*40000)us
// Duration*:    40000us      40000us      40000us      ...       40000us
//
//  *25fps = 0.04s per frame = 40000us per frame

#ifndef MEDIA_BASE_BUFFERS_H_
#define MEDIA_BASE_BUFFERS_H_

#include "base/basictypes.h"
#include "base/memory/ref_counted.h"
#include "base/time.h"
#include "media/base/media_export.h"

namespace media {

// Indicates an invalid or missing timestamp.
MEDIA_EXPORT extern inline base::TimeDelta kNoTimestamp() {
  return base::TimeDelta::FromMicroseconds(kint64min);
}

// Represents an infinite stream duration.
MEDIA_EXPORT extern inline base::TimeDelta kInfiniteDuration() {
  return base::TimeDelta::FromMicroseconds(kint64max);
}

class MEDIA_EXPORT Buffer : public base::RefCountedThreadSafe<Buffer> {
 public:
  // Returns a read only pointer to the buffer data.
  virtual const uint8* GetData() const = 0;

  // Returns the size of valid data in bytes.
  virtual int GetDataSize() const = 0;

  // If there's no data in this buffer, it represents end of stream.
  bool IsEndOfStream() const;

  base::TimeDelta GetTimestamp() const {
    return timestamp_;
  }
  void SetTimestamp(const base::TimeDelta& timestamp) {
    timestamp_ = timestamp;
  }

  base::TimeDelta GetDuration() const {
    return duration_;
  }
  void SetDuration(const base::TimeDelta& duration) {
    duration_ = duration;
  }

 protected:
  friend class base::RefCountedThreadSafe<Buffer>;
  Buffer(base::TimeDelta timestamp, base::TimeDelta duration);
  virtual ~Buffer();

 private:
  base::TimeDelta timestamp_;
  base::TimeDelta duration_;

  DISALLOW_COPY_AND_ASSIGN(Buffer);
};

}  // namespace media

#endif  // MEDIA_BASE_BUFFERS_H_